MTS 322 User Manual

be certain.

m

Series 322 Load Frames
Product Information

Model 322.21
Model 322.31
Model 322.41

011-551-601 C

Copyright information © 2009 MTS Systems Corporation. All rights reserved.

Trademark information MTS is a registered trademark of MTS Systems Corporation within the United

States. These trademarks may be protected in other countries. Molykote is a
registered trademark of Dow Chemical Corporation.

Publication information

MANUAL PART NUMBER PUBLICATION DATE

011-551-601 A Initial Release

011-551-601 B December 1992

011-551-601 C July 2009

2

Series Series 322 Load Unit

Technical Support

How to Get Technical Support

Start with your

manuals

Technical support

methods

The manuals supplied by MTS provide most of the information you need to use
and maintain your equipment. If your equipment includes software, look for
online help and README files that contain additional product information.

If you cannot find answers to your technical questions from these sources, you
can use the Internet, e-mail, telephone, or fax to contact MTS for assistance.

MTS provides a full range of support services after your system is installed. If
you have any questions about a system or product, contact Technical Support in
one of the following ways.

www.mts.com The web site provides access to our technical support staff by means of an

onlineform:

www.mts.com > Contact MTS > Service & Technical Support button

E-mail [e-mail]

Telephone MTS Call Center 800-328-2255

Weekdays 7:00 A.M. to 5:00 P.M., Central Time

Fax [phone]

Please include “Technical Support” in the subject line.

Outside the U.S. For technical support outside the United States, contact your local sales and

service office. For a list of worldwide sales and service locations and contact
information, use the Global MTS link at the MTS web site:

www.mts.com > Global MTS > (choose your region in the right-hand
column) > (choose the location closest to you)

Before You Contact MTS

MTS can help you more efficiently if you have the following information
available when you contact us for support.

Know your site

number and system

number

Series 322 Load Unit Technical Support

The site number contains your company number and identifies your equipment
type (such as material testing or simulation). The number is typically written on a
label on your equipment before the system leaves MTS. If you do not know your
MTS site number, contact your sales engineer.

Example site number: 571167

When you have more than one MTS system, the system job number identifies
your system. You can find your job number in your order paperwork.

Example system number: US1.42460

3

Know information from

prior technical

If you have contacted MTS about this problem before, we can recall your file
based on the:

assistance

• MTS notification number

• Name of the person who helped you

Identify the problem Describe the problem and know the answers to the following questions:

• How long and how often has the problem occurred?

• Can you reproduce the problem?

• Were any hardware or software changes made to the system before the

problem started?

• What are the equipment model numbers?

• What is the controller model (if applicable)?

• What is the system configuration?

Know relevant

computer information

Know relevant

software information

For a computer problem, have the following information available:

• Manufacturer’s name and model number

• Operating software type and service patch information

• Amount of system memory

• Amount of free space on the hard drive where the application resides

• Current status of hard-drive fragmentation

• Connection status to a corporate network

For software application problems, have the following information available:

• The software application’s name, version number, build number, and (if

available) software patch number. This information can typically be found
in the About selection in the Help menu.

• The names of other applications on your computer, such as:

– Anti-virus software

– Screen savers

– Keyboard enhancers

– Print spoolers

Technical Support

4

– Messaging applications

Series 322 Load Unit

If You Contact MTS by Phone

A Call Center agent registers your call before connecting you with a technical
support specialist. The agent asks you for your:

• Site number

• Name

• Company name

• Company address

• Phone number where you can be reached

If your issue has a notification number, please provide that number. A new issue
will be assigned a unique notification number.

Identify system type To enable the Call Center agent to connect you with the most qualified technical

support specialist available, identify your system as one of the following types:

• Electromechanical material test system

• Hydromechanical material test system

• Vehicle test system

• Vehicle component test system

Be prepared to

troubleshoot

Write down relevant

information

After you call MTS logs and tracks all calls to ensure that you receive assistance for your

• Aero test system

Prepare to perform troubleshooting while on the phone:

• Call from a telephone close to the system so that you can implement

suggestions made over the phone.

• Have the original operating and application software media available.

• If you are not familiar with all aspects of the equipment operation, have an

experienced user nearby to assist you.

In case Technical Support must call you:

• Verify the notification number.

• Record the name of the person who helped you.

• Write down any specific instructions.

problem or request. If you have questions about the status of your problem or
have additional information to report, please contact Technical Support again and
provide your original notification number.

Series 322 Load Unit Technical Support

5

Problem Submittal Form in MTS Manuals

Use the Problem Submittal Form to communicate problems with your software,
hardware, manuals, or service that are not resolved to your satisfaction through
the technical support process. The form includes check boxes that allow you to
indicate the urgency of your problem and your expectation of an acceptable
response time. We guarantee a timely response—your feedback is important to
us.

Access the Problem Submittal Form:

• In the back of many MTS manuals (postage paid form to be mailed to MTS)

• www.mts.com > Contact Us > Problem Submittal Form button (electronic

form to be e-mailed to MTS)

Technical Support

6

Series 322 Load Unit

Preface

Before You Begin

Safety first! Before you use your MTS product or system, read and understand the Safety

manual and any other safety information provided with your system. Improper
installation, operation, or maintenance can result in hazardous conditions that can
cause severe personal injury or death, or damage to your equipment and
specimen. Again, read and understand the safety information provided with your
system before you continue. It is very important that you remain aware of
hazards that apply to your system.

Other MTS manuals In addition to this manual, you may receive additional manuals in paper or

electronic form.

You may also receive an MTS System Documentation CD. It contains an
electronic copy of the manuals that pertain to your test system, such as:

• Hydraulic and mechanical component manuals

• Assembly drawings

• Parts lists

• Operation manual

• Preventive maintenance manual

Controller and application software manuals are typically included on the
software CD distribution disc(s).

Series 322 Load Unit Preface

7

Conventions

DANGER

WARNING

CAUTION

Conventions

Documentation Conventions

The following paragraphs describe some of the conventions that are used in your
MTS manuals.

Hazard conventions Hazard notices may be embedded in this manual. These notices contain safety

information that is specific to the activity to be performed. Hazard notices
immediately precede the step or procedure that may lead to an associated hazard.
Read all hazard notices carefully and follow all directions and recommendations.
Three different levels of hazard notices may appear in your manuals. Following
are examples of all three levels.

Note For general safety information, see the safety information provided with

your system.

Danger notices indicate the presence of a hazard with a high level of risk which,
if ignored, will result in death, severe personal injury, or substantial property
damage.

Warning notices indicate the presence of a hazard with a medium level of risk
which, if ignored, can result in death, severe personal injury, or substantial
property damage.

Caution notices indicate the presence of a hazard with a low level of risk which,
if ignored, could cause moderate or minor personal injury or equipment damage,
or could endanger test integrity.

Notes Notes provide additional information about operating your system or highlight

easily overlooked items. For example:

Note Resources that are put back on the hardware lists show up at the end of

the list.

Special terms The first occurrence of special terms is shown in italics.

Illustrations Illustrations appear in this manual to clarify text. They are examples only and do

not necessarily represent your actual system configuration, test application, or
software.

Electronic manual

conventions

This manual is available as an electronic document in the Portable Document
File (PDF) format. It can be viewed on any computer that has Adobe Acrobat
Reader installed.

Preface

8

Series 322 Load Unit

Conventions

Hypertext links The electronic document has many hypertext links displayed in a blue font. All

blue words in the body text, along with all contents entries and index page
numbers, are hypertext links. When you click a hypertext link, the application
jumps to the corresponding topic.

Series 322 Load Unit Preface

9

Conventions

10

Preface

Series 322 Load Unit

Introduction

Model 318

Model 322

Model 359

Typical Load Units

Load Unit: Overview

The load unit is the primary structure for most materials testing. It is a stand­alone testing unit. The load unit consists of the load frame plus additional parts,
such as hydraulic crosshead lifts and control modules. Load units come in
different sizes and shapes. The following illustration shows typical load units
with common accessories.

The load units are designed for testing materials. They can perform tension and
compression tests, fatigue and fracture mechanics tests, as well as other tests.
MTS manufactures a variety of grips, mounting fixtures, test area guards, and
environmental chambers that can be used with the load unit.

Series 322 Load Unit Introduction

11

What you

need to know

MTS Systems Corporation assumes that you know how to use your controller.
See the appropriate manual for information about performing any controller­related step in this manual’s procedures. You are expected to know how to
perform the following procedures:

• Turn hydraulic pressure on and off

• Select a control mode

• Adjust the actuator position

• Zero a sensor signal

• Zero a sensor output

• Use your grips and fixtures

• Define a simple test

• Run a test

12

Introduction

Series 322 Load Unit

322 Load Unit: Component Identification

11

1

12

2

8

5

7

9

10

3

6

4

10

9

7

11

Component Descriptions (part 1 of 2)

I

TEM COMPONENT DESCRIPTION

1 Crosshead

Moves the up and down the column to accommodate different sized
specimens and fixtures. The crosshead is stiff and light weight; it is one end of
the force train.

2 Crosshead locks

3 Crosshead lifts

Clamps the crosshead to the columns. The locks are hydraulically powered.

Raises and lowers the crosshead hydraulically to accommodate different
specimen sizes. The lifts are small hydraulic actuators.

Series 322 Load Unit Introduction

13

Component Descriptions (part 2 of 2)

I

TEM COMPONENT DESCRIPTION

4 Control panel

Grip controls

Crosshead lift
control

Emergency
Stop

5 Servovalve

6Isolation pads

7 Accumulators

8LVDT

9Manifold

10 Linear actuator

The Emergency Stop button is standard; the other controls are optional.

Clamps and unclamps the hydraulically controlled grips during specimen
installation and removal.

Controls the crosshead lifts to raise and lower the crosshead hydraulically.

Removes hydraulic pressure from the load unit and issues an interlock signal
to the controller to stop the test program.

Controls both the flow rate and the direction of fluid entering the actuators. It
determines how fast the actuator extends or retracts.

Dampens the natural frequency to about 20 Hz. Optional air inflated isolators
dampen the frequency to about 2 Hz.

Stores hydraulic fluid under pressure to increase the actuator’s response time.
One accumulator connects to the pressure line; the other to the return line.

Measures the displacement of the actuator’s travel. The linear variable
displacement transducer (LVDT) is located inside the actuator.

Serves as the junction point between the hydraulic power unit (HPU),
accumulators, servovalve, and actuator. The actuator manifold controls the
hydraulic circuit that connects the hydraulic components.

Applies axial forces to specimens. The actuator is a hydraulically powered
device that provides linear displacement of (or forces into) a specimen. Grips
and fixtures can be mounted to the actuator.

11 Force transducer

12 Lifting rings

Measures the axial forces applied to specimen.

Allows the load unit to be moved by lifting the entire load unit.

322 Load Unit: Component Description

The load unit is a stand alone testing structure. It consists of the following
components:

• Load frame

• Crosshead lifts and locks

• Manifold

–Actuators

– Servovalves

– Accumulators

• Transducers

• Grip controls

14

Introduction

Series 322 Load Unit

Load frame The load frame is the basic structure which provides the reaction mass for the

force train. The T-slot base of the load frame is one end of the reaction mass and
the crosshead is the other end of the reaction mass. Installing a specimen and
other fixtures or components between the load unit base and the crosshead create
a force train.

The load frame and the other hydraulic components mounted to it collectively
create the load unit. The base houses the actuators, servovalves, and hydraulic
manifold. The crosshead is mounted above the base by two columns. A control
panel lets you operate the crosshead lifts, locks, and grips to assist in specimen
installation procedures.

Crosshead lifts

and locks

The crosshead can be positioned anywhere along the load frame columns. It is
moved along the column with hydraulic lifts. When the crosshead is in an
appropriate test position, it is hydraulically clamped to that position. This lets
you change the load unit to test specimens of different lengths.

Actuator manifold The 298.XX or 293.XX actuator manifold (also called a hydraulic service

manifold or HSM) acts as the hydraulic interface between the HPU and the
components mounted to the manifold (actuator, servovalves, and accumulators)
of the load unit. It contains the required hydraulic porting and piping to
accommodate the hydraulic components. The manifold can also control the
hydraulic pressure to the load unit.

Actuators The 244 Actuator can be located in the middle of the load unit base or crosshead.

It is a hydraulically powered piston that applies linear displacement of (or load
into) a specimen. It can apply equal power in tension and compression. One end
of the test specimen is installed into a fixture which is mounted to the end of the
actuator rod.

The 215 Rotary Actuator can be mounted with appropriate fixturing to the T-slot
table. The rotary actuator applies angular displacement of (or torque into) a
specimen. It can apply equal power in a cloacwise or counterclockwise direction.

Servovalves The Series 252 Servovalves regulates the direction and flow of the hydraulic

fluid to and from a hydraulic actuator. The servovalve responds to the polarity
and magnitude of the command signal generated by the controller.

Accumulators The Series 111 Accumulators suppress line-pressure fluctuations. The load unit

includes a pressure-line accumulator to provide fluid storage so a constant line
pressure can be maintained at the servovalves for maximum performance. The
return-line accumulator minimizes return-line pressure fluctuations.

Pressure control The load unit can be configured for several pressure configurations. The free

flow configuration passes the hydraulic pressure from the HPU (or hydraulic
service manifold) through the manifold to the hydraulic components. The
hydraulic pressure options include on/off control, high/low/off control, and high/
low/off control with a proportional valve to ramp the pressure transitions.

Transducers The load unit includes a force transducer and an LVDT.

Series 322 Load Unit Introduction

15

Force The force transducer (also called load cell or force sensor) measures the amount

of tension or compression and rotational torque applied to it. It has four strain
gages that form a balanced Wheatstone bridge. When forces are applied to the
bridge, it becomes unbalanced and produces an electrical signal that is
proportional to the force applied to it. The force transducer is a resistive device
and requires a DC conditioner to process the axial signal from the Wheatstone
bridge.

LVDT The LVDT measures the linear actuator’s travel. The LVDT consists of a

transformer with one primary and two secondary coils wound on a common
cylinder. The coil is stationary inside the actuator. A core is attached to the piston
rod of the actuator. As it moves inside the coil, it produces an electrical signal
that represents the position of the piston rod. The phase of the signal indicates the
direction the actuator rod is moving. An LVDT requires an AC conditioner to
process the signal.

Grip controls The grip controls provide independent clamping control of the upper and lower

grips. The maximum pressure for the grip controls can be set up to 69 MPa
(10,000 psi). The pressure is factory set to 20 MPa (3000 psi); 45 MPa (6500
psi); or 69 MPa (10,000 psi) to accommodate a variety of grips manufactured by
MTS Systems Corporation. A front panel control allows the grip pressure to be
adjusted within the factory setting. A rate control sets how fast the grips open and
close.

16

Introduction

Series 322 Load Unit

322 Basic Specifications

f

a

b

c

d

e

Fatigue Ratings, Dimensions, and Weight

M

ODEL 322.21 MODEL 322.31 MODEL 322.41

Load unit fatigue rating 100 kN (22 kip) 250 kN (55 kip) 500 kN (110 kip)

*

A maximum specimen/grip clearance

B width between columns 533 mm (21.0 in) 635 mm (25.0 in) 762 mm (30.0 in)

C height — with standard columns

†

D table height 838 mm (33.0 in) 864 mm (34.0 in) 984 mm (38.7 in)

E table width — side-to-side, without lifts 711 mm (28.0 in) 864 mm (34.0 in) 1067 mm (42.0 in)

F width — side-to-side, with lifts

Depth — front-to-back (not shown)

Weight

§

‡

‡

* With a standard Series 661 Force Transducer and a fully retracted 150 mm (6 in) displacement actuator.
† With a table mounted actuator.
‡ On standard length tables.The control module’s position can increase the table’s width and depth.

§ Typical maximum weight with hydraulic locks, hydraulic lifts, and a standard dimension platen. Does not
include the weight of grips or other accessories.

1270 mm (50.0 in) 1575 mm (62.0 in) 2057 mm (81.0 in)

2489 mm (98 in) 3010 mm (118.5 in) 3677 mm (144.75 in)

864 mm (34.0 in) 1016 mm (40.0 in) 1219 mm (48.0 in)

1000 mm (40.0 in) 1000 mm (40.0 in) 1500 mm (60.0 in)

1370 kg (3000 lb) 2050 kg (4500 lb) 3870 kg (8500 lb)

Series 322 Load Unit Introduction

17

a

c

b

d

e

ANSI Standard B.5.1 T-Slot Dimension

*

MODEL T-BOLT SIZE ABCDE

332.21 0.75 in 0.81 in 1.21 in 0.62 in 0.59 in 1.44 in

322.31 1 in 1.06 in 1.82 in 1.00 in 0.82 in 1.82 in

322.41 1 in 1.06 in 1.82 in 1.00 in 0.82 in 1.82 in

* Minimum tolerances.

DIN Standard 650 T-Slot Dimension

*

MODEL T-BOLT SIZE ABCDE

332.21 22 mm 22 mm 38 mm 22 mm 16 mm 37 mm

322.31 28 mm 28 mm 48 mm 28 mm 20 mm 46 mm

322.41 28 mm 28 mm 48 mm 28 mm 20 mm 46 mm

* Minimum tolerances.

18

Introduction

Series 322 Load Unit

M

ODEL

d

a

b

e

h

f

g

c

T-slot Platen Dimensions — U.S. Customary

T-slot Platen Dimensions

A

*

B

CD

†

E

FG H

332.21 711 mm
(28.0 in)

322.31 864 mm
(34.0 in)

322.41 1067 mm
(42.0 in)

1000 mm
(40.0 in)

1000 mm
(40.0 in)

1500 mm
(60.0 in)

355.6 mm
(14.0 in)

431.8 mm
(17.0 in)

533.4 mm
(21.0 in)

508.0 mm
(20.0 in)

508.0 mm
(20.0 in)

762.0 mm
(30.0 in)

* Larger tables available.
† Distance to optional second actuator mounting position.

127.0 mm
(5.0 in)

152.4 mm
(6.0 in)

304.8 mm
(12.0 in)

228.6 mm
(9.0 in)

254.0 mm
(10.0 in)

304.8 mm
(12.0 in)

101.6 mm
(4.0 in)

127.0 mm
(5.0 in)

177.8 mm
(7.0 in)

127.0 mm
(5.0 in)

127.0 mm
(5.0 in)

127.0 mm
(5.0 in)

Series 322 Load Unit Introduction

19

cd

ab

Deflections and Spring Rates

322.21 322.31 322.41

Deflections

*

100 kN (22 kip) 250 kN (55 kip) 500 kN (110 kip)

A-B base 0.15 mm (0.006 in) 0.18 mm (0.007 in) 0.20 mm (0.008 in)

B-C columns 0.10 mm (0.004 in) 0.20 mm (0.006 in) 0.20 mm (0.008 in)

C-D crosshead 0.13 mm (0.005 in) 0.20 mm (0.010 in) 0.25 mm (0.10 in)

A-D overall frame 0.38 mm (.015 in) 0.53 mm (0.021 in) 0.66 mm (0.026 in)

Spring rates

*

2.6 x 108 N/m
(1.5 x 10

6 lb/in)

4.6 x 10
(2.6 x 10

8 N/m

6 lb/in)

7.4 x 10
(4.2 x 10

8 N/m

6 lb/in)

* Determined at each load unit’s full fatigue rating with its crosshead raised 50 in (1270 mm) above

the T-slot table.

Deflection rates can vary 20%, depending on the type of actuator and force transducer you use.

For the most accurate high frequency test results, use a Load Unit with a fatigue rating that is larger
than its actuator’s force rating. (A 322.31 Load Unit with a 55 kip fatigue rating and a 22 kip actuator
will be stiffer than a 322.21 Load Unit with a 22 kip fatigue rating and 22 kip actuator.)

20

Introduction

Series 322 Load Unit

Series 322 Load Unit Introduction

21

Series 661 Force Transducer: Specifications

The force transducer used with this system is a Series 661 Force Transducer. The
following are the specifications for the force transducers.

ARAMETER SPECIFICATION

P

Maximum excitation voltage 15 V DC

Bridge resistance 350 ¾

Maximum crosstalk 1.0% of full scale torsional to load

Hysteresis 0.08% of full scale (250 N–2.5 kN)

Nonlinearity 0.08% of full scale

0.05% of full scale (5 kN–50 kN)

0.15% of full scale (100 kN–500 kN)

0.20% of full scale (1000 kN)

0.15% of full scale for Models 661.22/.23/.31

MODEL LOAD CAPACITY

661.11-01 250 N
(50 lbf)

661.11-02 500 N
(100 lbf)

661.18-01 1 kN
(220 lbf)

661.18-02 2.5 kN
(550 lbf)

661.19-01 5 kN
(550 lbf)

Temperature

Usable range
Compensated range
Sensitivity

Output 2 mV/V at full-scale load

Connector PT02ER-10-6P

M6 x 1.0 mm x 6.3 mm
(1/4 - 28 UNF x 0.25 in

M6 x 1.0 mm x 6.3 mm
(1/4 - 28 UNF x 0.5 in

M12 x 1.25 mm x 25.4 mm
(1/2 - 20 UNF x 1.0 in)

M12 x 1.25 mm x 25.4 mm
(1/2 - 20 UNF x 1.0 in)

M12 x 1.25 mm x 25.4 mm
(1/2 - 20 UNF x 1.0 in)

0.004% of reading/°C (0.002%/°F)

-54°C (-65°F) to +121°C (+250°F)
+21°C (+70°F) to +77°C (+170°F)

0.0036% of full scale/°C
(0.0020% of full scale/°F)

THREAD SIZE

*

0.45 kg
(1 lb)

0.45 kg
(1 lb)

2.27 kg
(5 lb)

2.27 kg
(5 lb)

3.07 kg
(6.75 lb)

WEIGHT

661.19-02 10 kN
(2.2 kip)

661.19-03 15 kN
(3.3 kip)

661.19-04 25 kN
(5.5 kip)

Introduction

22

M12 x 1.25 mm x 25.4 mm
(1/2 - 20 UNF x 1.0 in)

M12 x 1.25 mm x 25.4 mm
(1/2 - 20 UNF x 1.0 in)

M12 x 1.25 mm x 25.4 mm
(1/2 - 20 UNF x 1.0 in)

3.07 kg
(6.75 lb)

3.07 kg
(6.75 lb)

3.07 kg
(6.75 lb)

Series 322 Load Unit

MODEL LOAD CAPACITY

A

B

C

D

E

THREAD SIZE

*

WEIGHT

661.20-01 25 kN
(5.5 kip)

661.20-02 50 kN
(11 kip)

661.20-03 100 kN
(2.2 kip)

661.22-01 250 kN
(3.3 kip)

661.23-01 500 kN
(5.5 kip)

661.31-01 1000 kN
(220 kip)

* The thread sizes are available with either coarse or fine threads.

M27 x 2.0 mm x 31.7 mm
(1 - 14 UNS-3B x 1.25 in)

M27 x 2.0 mm x 31.7 mm
(1 - 14 UNS-3B x 1.25 in)

M27 x 2.0 mm x 31.7 mm
(1 - 14 UNS-3B x 1.25 in)

M36 x 2.0 mm
(1 1/2 - 12 UNC-2B)

M52 x 2.0 mm x 48.3 mm
(2.0 - 12 UN-2B x 1.9 in)

M76 x 1.75 mm x 28.4 mm
(2.0 - 12 UN-2B x 1.35 in)

Dimensions The following dimensions are rounded off to the nearest millimeter or eight-inch.

9.75 kg
(21.5 lb)

9.75 kg
(21.5 lb)

9.75 kg
(21.5 lb)

13.2 kg
(29 lb)

16 kg
(35.3 lb)

49.9 kg
(110 lb)

MODEL A

661.11-01 70 mm

(2–3/4 in)

661.18-01 105 mm

(4–1/4 in)

661.19-01 105 mm

(4–1/4 in)

661.20-01 154 mm

(6 in)

661.22-01 114 mm

(4–1/2 in)

661.23-01 152 mm

(6 in)

661.31-01 222 mm

(8–3/4 in)

* This dimension applies to both ends

Series 322 Load Unit Introduction

18 mm
(3/4 in)

32 mm
(1–1/4 in)

32 mm
(1–1/4 in)

57 mm
(2–1/4 in)

92 mm
(3–5/8 in)

140 mm
(5–1/5 in)

203 mm
(8 in)

*

B

CD*E

7 mm
(1/4 in)

7 mm
(1/4 in)

7 mm
(1/4 in)

10 mm
(3/8 in)

1 mm
(>1/4 in)

N/A 203 mm

N/A 305 mm

38 mm
(1–1/5 in)

67 mm
(2–5/8 in)

67 mm
(2-5/8 in)

95 mm
(3–3/4n)

203 mm
(8 in)

(8 in)

(12 in)

61 mm
(2–3/8 in

64 mm
(2–1/5 in)

64 mm
(2–1/5 in)

89 mm
(3–1/2 in)

74 mm
(2–7/8 in)

86 mm
(3–3/8 in)

124 mm
(4–7/8 in)

23

24

Introduction

Series 322 Load Unit

Safety

General Safety Practices

This section provides information about safety issues that pertain to
servohydraulic systems in general. These issues include statements to the
intended use and foreseeable misuse of the system, the hazard zone, definition for
the graphical hazard labeling that is affixed to your product, and other (more
general) safety information that relates to the high-pressure and high­performance characteristics of MTS servohydraulic systems.

MTS test systems are designed to generate motions and forces and impart these
motions and forces into a test specimen.

When you prepare to operate the system and during system operation, ensure the
following:

• Do not use or allow personnel to operate the system who are not

• Do not disable safety components or features (including limit detectors,

experienced, trained, or educated in the inherent dangers associated with
high-performance servo hydraulics and who are not experienced, trained, or
educated with regard to the intended operation as it applies to this test
system.

light curtains, or proximity switches/detectors).

• Do not attempt to operate the system without appropriate personal safety

gear (for example, hearing, hand, and eye protection).

• Do not apply energy levels that exceed the maximum energies and velocities

for the system design. Refer to the system specifications.

• Do not test a specimen that exceeds the minimum (if applicable) or

maximum allowable mass. Refer to the system specifications.

• Do not use specimens that are combustible, flammable, pressurized, or

explosive.

• Do not use humans as specimens or allow humans to ride in or on the test

specimen or the test system for any purpose unless the system is man-rated
and all associated safety conditions are strictly enforced.

• Do not modify the system or replace system components using parts that are

not MTS component parts or effect repairs using parts or components that
are not manufactured to MTS specifications.

• Do not operate the system in an explosive atmosphere.

• Do not use the system in a test area where uncontrolled access to the test

system is allowed when the system is in operation

• Do not operate the system unless an interlock is installed to monitor supply

pressure into the HSM and initiate a system interlock if a low or no pressure
event occurs.

Series 322 Load Unit Safety

25

If you have system related responsibilities (that is, if you are an operator, service
engineer, or maintenance person), you should study safety information carefully
before you attempt to perform any test system procedure.

You should receive training on this system or a similar system to ensure a
thorough knowledge of your equipment and the safety issues that are associated
with its use. In addition, you should gain an understanding of system functions
by studying the other manuals supplied with your test system. Contact MTS for
information about the content and dates of training classes that are offered.

It is very important that you study the following safety information to ensure that
your facility procedures and the system’s operating environment do not
contribute to or result in a hazardous situation. Remember, you cannot eliminate
all the hazards associated with this system, so you must learn and remain aware
of the hazards that apply to your system at all times. Use these safety guidelines
to help learn and identify hazards so that you can establish appropriate training
and operating procedures and acquire appropriate safety equipment (such as
gloves, goggles, and hearing protection).

Each test system operates within a unique environment which includes the
following known variables:

• Facility variables (facility variables include the structure, atmosphere, and

utilities)

• Unauthorized customer modifications to the equipment

• Operator experience and specialization

• Test specimens

Because of these variables (and the possibility of others), your system can
operate under unforeseen circumstances that can result in an operating
environment with unknown hazards.

Improper installation, operation, or maintenance of your system can result in
hazardous conditions that can cause death, personal injury, or damage to the
equipment or to the specimen. Common sense and a thorough knowledge of the
system’s operating capabilities can help to determine an appropriate and safe
approach to its operation.

Safety Practices Before System Operation

Before you apply hydraulic power to the test system, review and complete all of
the safety practices that are applicable to your system. The goal, by doing this, is
to improve the safety awareness of all personnel involved with the system and to
maintain, through visual inspections, the integrity of specific system
components.

Read all manuals Study the contents of this manual and the other manuals provided with your

system before attempting to perform any system function for the first time.
Procedures that seem relatively simple or intuitively obvious can require a
complete understanding of system operation to avoid unsafe or dangerous
situations.

26

Safety

Series 322 Load Unit

Locate and read

hazard placards/labels

Find, read, and follow the hazard placard instructions located on the equipment.
These placards are placed strategically on the equipment to call attention to areas
such as known crush points and electrical voltage hazards.

Locate Lockout/tagout

points

Know facility safe

procedures

Locate Emergency

Stop buttons

Know where the lockout/tagout point is for all of the supply energies associated
with your system. This includes the hydraulic, pneumatic, electric, and water
supplies (as appropriate) for your system to ensure that the system is isolated
from these energies when required.

Most facilities have internal procedures and rules regarding safe practices within
the facility. Be aware of these safe practices and incorporate them into your daily
operation of the system.

Know the location of all the system Emergency Stop buttons so that you can
stop the system quickly in an emergency. Ensure that an Emergency Stop button
is located within 2 meters (6 feet) of the operator at all times.

Know controls Before you operate the system for the first time, make a trial run through the

operating procedures with the power off. Locate all hardware and software
controls and know what their functions are and what adjustments they require. If
any control function or operating adjustment is not clear, review the applicable
information until you understand it thoroughly.

Have first aid available Accidents can happen even when you are careful. Arrange your operator

schedules so that a properly trained person is always close by to render first aid.
In addition, ensure that local emergency contact information is posted clearly and
in sight of the system operator.

Know potential crush

and pinch points

Be aware of potential crush and pinch points on your system and keep personnel
and equipment clear of these areas.

Be aware of

component movement

with hydraulics off

Know electrical

hazards

Remember, when hydraulic power is interrupted on a servohydraulic system, it is
likely that stored accumulator pressure will persist for some time within the
system. In addition, it is likely that as stored energy dissipates, gravity will cause
portions of the system to move.

The crosshead can slowly drift down the columns if the locks are turned off and
when hydraulic pressure is turned off. The crosshead can damage any test
fixtures, grips, and specimen in its path. Unlock the crosshead only to reposition
it. Always lock the crosshead after you have repositioned it and never leave the
crosshead unlocked.

The actuator rod can also drift down when hydraulics are turned off hitting
anything in its path. This uncommanded movement is because of oil movement
between the pressure/return ports and oil blow by across the piston hub. Be aware
that this can happen and clear the area around the actuator rod when hydraulics
are turned off.

When the system electrical power is turned on, minimize the potential for
electrical shock hazards. Wear clothing and use tools that are properly insulated
for electrical work. Avoid contact with exposed wiring or switch contacts.

Whenever possible, turn off electrical power when you work on or in proximity
to any electrical system component. Observe the same precautions as those given
for any other high-voltage machinery.

Series 322 Load Unit Safety

27

Keep bystanders

safely away

Keep bystanders at a safe distance from all equipment. Never allow bystanders to
touch specimens or equipment while the test is running.

Wear proper clothing Do not wear neckties, shop aprons, loose clothing or jewelry, or long hair that

could get caught in equipment and result in an injury. Remove loose clothing or
jewelry and restrain long hair.

Remove flammable

fluids

Know compressed gas

hazards

Remove flammable fluids from their containers or from components before you
install the container or component. If desired, you can replace the flammable
fluid with a non-flammable fluid to maintain the proper proportion of weight and
balance.

Most servohydraulic systems contain accumulators that require a high-pressure
gas precharge (pressures that exceed 138 bar [2000 psi]). In addition, some
systems can contain devices, such as static supports, that are pneumatically
operated. High-pressure devices are potentially dangerous because a great
amount of energy is available in the event of an uncontrolled expansion or
rupture.

28

Safety

Series 322 Load Unit

Observe the following safety practices when you work with high-pressure air or
gases:

• When you charge an accumulator, follow all the charging instructions

provided in the appropriate product information manuals. When precharging
accumulators, properly identify the type of gas to be used and the type of
accumulator to be precharged.

Use only dry-pumped nitrogen to precharge nitrogen-charged accumulators.
(Dry-pumped nitrogen can also be labeled “oil pumped” or “dry water
pumped.”) Do not use compressed air or oxygen for precharging: the
temperature increase caused by rapid gas compression can result in highly
explosive conditions when hydraulic fluid is in the presence of oxygen or
compressed air.

• Always follow the recommended bleeding procedures before you remove or

disassemble components that contain pressurized gas. When you bleed a gas
or remove a fitting, hose, or component that contains a gas, remember that
many gases cannot support life. Therefore, as the ratio of released gas to
oxygen increases, so does the potential for suffocation.

• Wear appropriate safety devices to protect your hearing. Escaping air or gas

can create a noise level that can damage your hearing.

• Ensure that all pressurized air or gas is bled out of a pneumatic or gas-

charged device before you start to disassemble it. A thorough understanding
of the assembly and its pressurized areas is necessary before you undertake
any maintenance. Refer to the appropriate product information for the
correct bleeding procedure.

Check bolt ratings and

torques

It might not be obvious or intuitive which bolts or fittings are used to
restrain a pressurized area. On some assemblies, you must remove a cover
plate to gain access to the structural bolts. Sometimes, to protect you from a
rapid release of trapped gases, a small port is exposed when you remove this
cover plate. Exposing this port ensures that the gas precharge is fully bled
before disassembly. However, this is not the recommended procedure for
bleeding a pneumatic or gas-charged device, because it can expose you to
the dangers of escaping compressed gas and particulates that are expelled
from the chamber or around the seals. Do not assume that cover plates and
ports are installed in all the critical locations.

Consult MTS when in doubt about the safety or reliability of any system-related
procedure or modification that involves devices that contain any type of
compressed gas.

To ensure a reliable product, fasteners (such as bolts and tie rods) used in MTS­manufactured systems are torqued to specific requirements. If a fastener is
loosened or the configuration of a component within the system is modified, refer
to the system and component assembly drawings (located on the System
Documentation CD) to determine the correct fastener, fastener rating, and torque.
Overtorquing or undertorquing a fastener can create a hazardous situation due to
the high forces and pressures present in MTS test systems.

Series 322 Load Unit Safety

29

On rare occasions, a fastener can fail even when it is correctly installed. Failure
usually occurs during torquing, but it can occur several days later. Failure of a
fastener can result in a high velocity projectile. Therefore, it is a good practice to
avoid stationing personnel in line with or below assemblies that contain large or
long fasteners.

Practice good

housekeeping

Protect hoses and

cables

Provide proper

hydraulic fluid

filtration.

Protect accumulators

from moving objects.

Keep the floors in the work area clean. Hydraulic fluid that is spilled on any type
of floor can result in a dangerous, slippery surface. Do not leave tools, fixtures,
or other items not specific to the test, lying about on the floor, system, or decking.

Protect electrical cables from spilled hydraulic fluid and from excessive
temperatures that can cause the cables to harden and eventually fail. Ensure that
all cables have appropriate strain relief devices installed at the cable and near the
connector plug. Do not use the connector plug as a strain relief.

Protect all system hoses and cables from sharp or abrasive objects that can cause
the hose or cable to fail. Never walk on hoses or cables or move heavy objects
over them. Consider hydraulic distribution system layout and route hoses and
cables away from areas that expose them to possible damage.

When removing hydraulic hoses for equipment repair or changing testing
components (for example, hydraulic grips), make sure to cap the hose ends to
avoid spilling hydraulic fluid.

If the system is equipped with a non-MTS hydraulic power unit, ensure proper
filtration to the hydraulic distribution system and testing components. Particles
present in hydraulic fluid and cause erratic or poor system response.

Protect accumulators with supports or guards. Do not strike accumulators with
moving objects. This could cause the accumulator(s) to separate from the
manifold resulting in equipment damage and personal injury.

Record changes If you change any operating procedure, write the change and the date of the

change in the appropriate manual.

Provide test area

guards

Do not exceed the

Maximum Supply

Pressure

Do not disable safety

devices

Use appropriately

sized fuses

Use protective guards such as cages, enclosures, and special laboratory layouts
when you work with hazardous test specimens (for example, brittle or
fragmenting materials or materials that are internally pressurized).

For standard MTS systems, ensure that hydraulic supply pressure is limited to a
maximum 21 MPa (3000 psi). If you system has a custom application that
requires higher pressure, make sure you limit supply pressure to that rated for the
custom components.

Your system might have active or passive safety devices installed to prevent
system operation if the device indicates an unsafe condition. Do not disable such
devices as it can result in unexpected system motion.

Whenever you replace fuses for the system or supply, ensure that you use a fuse
that is appropriately sized and correctly installed. Undersized or oversized fuses
can result in cables that overheat and fuses that explode. Either instance creates a
fire hazard.

30

Safety

Series 322 Load Unit

Provide adequate

lighting

Ensure adequate lighting to minimize the chance of operation errors, equipment
damage, and personal injury. You need to see what you are doing.

Provide means to

access out-of-reach

components

Ensure equipment is

secure

Make sure you can access system components that might be out of reach while
standing on the floor. For example ladders or scaffolding might be required to
reach load cell connectors on tall load units.

Make sure the equipment is secure or provide vibration isolation. Some testing
can be performed at resonant frequencies that might cause the equipment to
vibrate and move during testing.

Safety Practices While the System Is in Operation

Wear appropriate

personal protection

Provide test area

guards

Wear eye protection when you work with high-pressure hydraulic fluid,
breakable specimens, or when anything characteristic to the specimen could
break apart.

Wear ear protection when you work near electric motors, pumps, or other devices
that generate high noise levels. Some systems can create sound pressure levels
that exceed 70 dbA during operation.

Wear appropriate personal protection equipment (gloves, boots, suits, respirators)
whenever you work with fluids, chemicals, or powders that can irritate or harm
the skin, respiratory system, or eyes.

Use protective guards such as cages, enclosures, and special laboratory layouts
when you work with hazardous test specimens (for example, brittle or
fragmenting materials or materials that are internally pressurized).

Specimen temperature

changes

Handle chemicals

safely

Know servohydraulic

system interlocks

During cyclic testing, the specimen temperature can become hot enough to cause
burns. Wear personal protection equipment (gloves) when handling specimens.

Whenever you use or handle chemicals (for example, hydraulic fluid, batteries,
contaminated parts, electrical fluids, and maintenance waste), refer to the
appropriate MSDS documentation for that material and determine the appropriate
measures and equipment required to handle and use the chemical safely. Ensure
that the chemical is disposed of appropriately.

Interlock devices should always be used and properly adjusted. Interlock devices
are designed to minimize the chance of accidental damage to the test specimen or
the equipment. Test all interlock devices for proper operation immediately before
a test. Do not disable or bypass any interlock devices as doing so could allow
hydraulic pressure to be applied regardless of the true interlock condition. The
Reset/Override button is a software function that can be used to temporarily
override an interlock while attempting to start the hydraulic power unit and gain
control of the system.

Know system limits Never rely on system limits such as mechanical limits or software limits to

protect you or any personnel. System limits are designed to minimize the chance
of accidental damage to test specimens or to equipment. Test all limits for proper
operation immediately before a test. Always use these limits and adjust them
properly.

Series 322 Load Unit Safety

31

Do not disturb sensors Do not bump, wiggle, adjust, disconnect, or otherwise disturb a sensor (such as

an accelerometer or extensometer) or its connecting cable when hydraulic
pressure is applied.

Ensure secure cables Do not change any cable connections when electrical power or hydraulic pressure

is applied. If you attempt to change a cable connection while the system is in
operation, an open control loop condition can result. An open control loop
condition can cause a rapid, unexpected system response which can result in
severe personal injury, death, or damage to equipment. Also, ensure that all
cables are connected after you make any changes in the system configuration.

Stay alert Avoid long periods of work without adequate rest. In addition, avoid long periods

of repetitious, unvarying, or monotonous work because these conditions can
contribute to accidents and hazardous situations. If you are too familiar with the
work environment, it is easy to overlook potential hazards that exist in that
environment.

Contain small leaks Do not use your fingers or hands to stop small leaks in hydraulic or pneumatic

hoses. Substantial pressures can build up, especially if the hole is small. These
high pressures can cause the oil or gas to penetrate your skin, causing painful and
dangerously infected wounds. Turn off the hydraulic supply and allow the
hydraulic pressure to dissipate before you remove and replace the hose or any
pressurized component.

Stay clear of moving

equipment/avoid crush

points

Know the causes of

unexpected actuator

motions

Do not use RF

transmitters

Stay clear of mechanical linkages, connecting cables, and hoses that move
because you can get pinched, crushed, tangled, or dragged along with the
equipment. High forces generated by the system can pinch, cut, or crush anything
in the path of the equipment and cause serious injury. Stay clear of any potential
crush points. Most test systems can produce sudden, high-force motion. Never
assume that your reactions are fast enough to allow you to escape injury when a
system fails.

The high force and velocity capabilities of MTS actuators can be destructive and
dangerous (especially if actuator motion is unexpected). The most likely causes
of unexpected actuator response are operator error and equipment failure due to
damage or abuse (such as broken, cut, or crushed cables and hoses; shorted wires;
overstressed feedback devices; and damaged components within the servocontrol
loop). Eliminate any condition that could cause unexpected actuator motion.

Keep radio frequency (RF) transmitters away from the workstation computers,
remote terminals, and electronics consoles. Intense RF fields can cause erratic
operation of the more sensitive circuits in the system.

32

Safety

Series 322 Load Unit

Hazard Icons

I

CON DESCRIPTION

Moving parts; pinch points. Keep clear of areas
noted with this label

High pressure fluid or gasses. Do not tamper with
fittings or hoses.

Possible explosive or flying debris. Wear
appropriate protection such as safety goggles and
hearing protection.

Following are the hazard icons used on the MTS products.

Possible tipping hazard. The machine should only
be moved by qualified riggers familiar with moving
heavy, delicate equipment. Once in final operation
position, the frame should be bolted to a suitable
reaction mass.

Alternate possible tipping hazard. The machine
should only be moved by qualified riggers familiar
with moving heavy, delicate equipment. Once in
final operation position, the frame should be bolted
to a suitable reaction mass.

Read the manuals or instructions. Become familiar
with safety information. Also become familiar with
operating and maintenance information.

Series 322 Load Unit Safety

33

I

CON DESCRIPTION

Alternate read the manuals or instructions. Become
familiar with safety information. Also become
familiar with operating and maintenance
information.

Hot surfaces. Possible burn hazard. Wear personal
protective equipment such as gloves when working
near hot surfaces.

Object is heavy. Requires more that one person to
lift and move.

34

Safety

Series 322 Load Unit

322 Load Unit: Hazard Labels

Preloader torque
lube and torque
xxx N·m xxx ft-lbf

! Warning
If lift cylinder line is opened,
air may enter, causing
crosshead to drop when
unlocked. Bleed both
cylinders before unlocking
crosshead.

! Warning
High force moving parts. Can
cause severe injury or equipment
damage. Stay clear and use eye
protection while test is in
progress. Read instructions
before operating or servicing.

Hydraulic Actuator
model no.
assembly no.
force kip kN
area in2 cm2
stroke dyn. static in.

dyn. static mm

! Warning
Subjecting this equipment to
pressures above 3000 psi (20.7 MPa)
can result in component rupture and
injury to personnel. See the product
manual for safety precautions before
operating.

Front

This section provides information on hazard labeling. Part numbers are provided
should replacement labels be necessary due to damage.

Series 322 Load Unit Safety

35

Force Transducer
model s/n
cpty kN lbs

! Warning
High force moving parts. Can cause
severe injury or equipment damage.
Stay clear and use eye protection
while test is in progress. Read
instructions before operating or
servicing.

! Warning
If lift cylinder line is opened, air
may enter, causing crosshead to
drop when unlocked. Bleed both
cylinders before unlocking
crosshead.

Service Manifold
model no. s/n
ass’y no. rev.
3000 psi 20.7 MPa

Piston Accumulator
pressure psi MPa
model s/n

! Danger
Nitrogen under pressure. Do not
test or disassemble without
adequate instructions.

Load Unit
model no.
part no. rev.
serial no.
force cpty.
mg. date

Rear

36

Safety

Series 322 Load Unit

322 Load Unit: Crush Point Hazards

Crush
point
areas

It is important to stay clear of any potential crush points when the system is
operating. Know where the crush points are in your system and protect yourself
and others from those crush points with appropriate safety devices. The
following paragraphs describe crush points and precautions to take while
working around crush points.

Locations A crush point exists between the platen and crosshead on load units where the

actuator piston rod and specimen move (both areas are shown). Another potential
crush point exists where the lower end of the actuator piston rod extends below
the platen and the bottom of the load unit/load frame.

Precautions Keep clear of any mechanical linkage that moves within a closed area. If the

linkage should move (when the system starts or due to mechanical failure), very
high forces can be present that could pinch, cut, or crush anything in the path of
linkage movement.

Never allow any part of your body to enter the path of machine movement or to
touch moving machinery, linkages, hoses, cables, and specimens. These present
serious crush points or pinch points.

Series 322 Load Unit Safety

37

38

Safety

Series 322 Load Unit

Installation

Inspect for Shipping Damage

Load Unit installation consists of these four major tasks —

• Inspect for Shipping Damage

• Unpack and Move the Platen

• Install the Crosshead Assembly

• Make Connections, Bleed Lifts, Tighten Columns

Special equipment needed —

• An overhead crane and lifting slings or chains capable of lifting the load unit

Load Unit Standard Dimension Platen Weight

322.21 28 X 40 in 711 X 1016 mm 3000 lb 1370 kg

322.31 34 X 40 in 864 X 1016 mm 4500 lb 2050 kg

322.41 42 X 60 in 1067 X 1524 mm 8500 lb 3870 kg

• Torque wrenches: 322.21 – 700 lbf·ft (950 N·m) capacity

• Molykote G-n paste

Inspect for Shipping Damage

Look for the following:

• Scratches in the load unit or lift cylinder columns

• Damaged electrical connections

• Damaged hydraulic connections

• Dents and other structural damage

• Torn, kinked, or breaking hoses

Report any damage found to both the carrier and MTS. In the U.S. and Canada,
call the MTS HELPLine at 1-800-328-2255. Elsewhere, contact your local MTS
office.

322.31 – 1400 lbf·ft (1900 N·m) capacity

322.41 – 1400 lbf·ft (1900 N·m) capacity

Series 322 Load Unit Installation

39

Unpack and Move the Platen

Unpack and Move the Platen

Note You can move the platen and crosshead assembly with a forklift as long

as they’re attached to their pallets.

The load unit is extremely heavy.

The weight of the load unit can seriously hurt you and damage your load
unit.

Do not allow the load unit to drop or topple. Observe the following precautions:

• Ensure that your chains, slings, and crane have a working capacity greater

than the load unit’s weight.

• Ensure that the lifting eyebolts are tight.

• Ensure that the crosshead locking bolts are fully tightened.

• Lift the load unit only high enough to clear its pallet.

• Operate the crane smoothly to prevent sudden shocks to the sling.

1. Remove the pallet’s plywood sheeting if used.

2. Tighten the platen’s four lifting eyes.

3. Remove the lumber and cut the straps that tie the pallet to the platen.

40

Installation

Series 322 Load Unit

Unpack and Move the Platen

Attach straps

30° maximum

4. Attach the lifting straps to the lifting eyes.

Adjust them so each lifts about

the same weight.

Keep your straps as straight as possible — do not let them get more than 30°
from the vertical.

5. Lift the platen clear of its pallet and move it carefully to its installation site.

6. Lower the platen onto the isolation pads. If the platen is not level, install
stock metal shims between the pads and the floor.

Series 322 Load Unit Installation

41

Install the Crosshead Assembly

Install the Crosshead Assembly

There is a possibility of the crosshead assembly suddenly dropping —

You can be seriously hurt and your assembly badly damaged.

To reduce the hazards in this procedure, observe the following precautions:

• Always lift the crosshead assembly using the lifting eyes screwed into the

crosshead — never with eyes screwed into the columns.

• Never wrap chains around the crosshead or columns or actuator.

• Smoothly lift, move, and lower the crosshead assembly to avoid shocks that

could break the chain, crane, or lifting eyes.

• Lift the crosshead assembly no higher than is needed to install it.

Note Lightly lube all threads with Molykote G-n paste.

42

Installation

Series 322 Load Unit

1. Tighten the crosshead manual locking bolts.

Load Unit Rating 100 kN (22 kip)

100 N·m (140 lbf·ft)

Load Unit Rating 250 kN (55 kip)

271 N·m (200 lbf·ft)

Load Unit Rating 500 kN (110 kip)

Rear

271 N·m (200 lbf·ft)

Load Unit Rating 500 kN (110 kip)

Front

271 N·m (200 lbf·ft)

Install the Crosshead Assembly

Manually locked

crosshead

Check the torque on the locking bolts, following the pattern in the following

Make sure the locks are tight.

figure.

Series 322 Load Unit Installation

43

Install the Crosshead Assembly

3

4

1

2

3

4

11

2

1

2

Load Unit Rating 100 kN (22 kip)

100 N·m (140 lbf·ft)

Load Unit Rating 250 kN (55 kip)

271 N·m (200 lbf·ft)

Load Unit Rating 500 kN (110 kip)

271 N·m (200 lbf·ft)

Do not tighten the bolts for the hydraulic locks.

Mistakenly tightening the bolts for the hydraulic locks along with the crosshead’s
manual locking bolts could make the crosshead bind when it’s unlocked causing
personal injury and equipment damage.

Hydraulically locked

crosshead

Tighten the manual locking bolts, following the pattern in this figure. Make sure
the locks are tight.

2. Make sure the crosshead’s lifting eyes are tight.

3. Cut the straps that tie the crosshead assembly to the platen.

44

Installation

Series 322 Load Unit

Install the Crosshead Assembly

Attach straps

Raise

4. Attach the lifting straps to the lifting eyes. Slowly and carefully bring the
assembly to an upright position.

Series 322 Load Unit Installation

45

Install the Crosshead Assembly

25% of full torque

5. Attach the crosshead assembly to the platen. Tighten the column cap screws
to 25% of their full torque value.

Load Unit Rating

100 kN (22 kip)

170 lbf·ft 240 N·m 350 lbf·ft 475 N·m 350 lbf·ft 475 N·m

Load Unit Rating

250 kN (55 kip)

Load Unit Rating

500 kN (110 kip)

Installation

46

Series 322 Load Unit

Install the Crosshead Assembly

110 N·m (80 lbf·ft)

Clamp position mark

75 N·m (55 lbf·ft)

Parallel

Connect

Note Skip the next two steps if you do not have hydraulic lifts.

6. Assemble the cylinder clamp around the lift cylinder. Start the clamp’s cap

screws into the platen. Use the cylinder’s clamp marks to get its height right.
Get the cylinder parallel to the column. Torque the cap screws to 55 lbf·ft
(75 N·m).

A. If the lift bracket has been removed, reinstall it, hand tightening the cap

screw that goes into the crosshead.

B. Raise the piston. Hand tighten the cap screw that goes into the piston.

C. Torque the crosshead’s cap screw to 34 lbf·ft (46 N·m). Torque the

piston’s cap screw to 80 lbf·ft (110 N·m).

D. Repeat this step to install the other lift cylinder.

7. Connect the hose at the cylinders’ end caps.

Series 322 Load Unit Installation

47

Make Connections, Bleed Lifts, Tighten Columns

Hydraulic lock hoses

Force transducer cable

Emergency Stop cable

Pressure and return lines

Servovalve cable

Pilot pressure line

Lift cylinder lines

LVDT cable

Make Connections, Bleed Lifts, Tighten Columns

1. Make all hydraulic and electrical connections to the load unit.

Air trapped in the lifts may let the crosshead drop as soon as you unlock it.

You can be hurt and your load unit damaged.

After installation, always bleed the lifts before unlocking the crosshead.

48

Installation

Series 322 Load Unit

Make Connections, Bleed Lifts, Tighten Columns

3

4

1

2

3

4

11

2

1

2

Load Unit Rating 100 kN (22 kip)

Load Unit Rating 250 kN (55 kip)

Load Unit Rating 500 kN (110 kip)

2. Bleed Hydraulic Lift Cylinders.

Bleed both hydraulic lift cylinders. Refer to “Load Unit: Bleed the

Hydraulic Lift Cylinders” on page 69 for the procedure.

Mistakenly loosening the bolts for the hydraulic locks along with the
crosshead’s manual locking bolts could let the crosshead slip, especially
when it is under load.

You could be hurt and your equipment damaged.

3. If your load unit has hydraulic locks, loosen the crosshead’s manual locking
bolts following the pattern in the following figure.

4. Unlock the crosshead. Raise and lower your crosshead several times. This
aligns the columns to the crosshead travel before final torque is applied to
the column cap screws.

Series 322 Load Unit Installation

49

Make Connections, Bleed Lifts, Tighten Columns

100% torque

5. Tighten the column cap screws to their full torque values.

322.21 322.31 322.41

680 lbf·ft 920 N·m 1360 lbf·ft 1840 N·m 1360 lbf·ft 1840 N·m

6. Check the alignment of the force transducer with the actuator.

50

Installation

Series 322 Load Unit

Operation

CAUTION

Load Unit: Operation Preface

This section describes the load unit controls, crush point hazards, and procedures
performed during the normal, day-to-day operation of the load unit.

Application note Special considerations must be followed when using low force transducers in a

high force systems. Small force transducers are commonly used in larger
systems. You need to be aware that the load unit can produce forces that exceed
the rating of the low force transducer.

Low force transducers in high force systems can be exposed to excessive
forces.

Applying forces that exceed the rated capacity of the force transducer can
damage the transducer.

Ensure that all test commands are within the force transducer’s rating when it is
installed. Your warranty does not cover damage caused by a high force actuator.

MTS recommends the following:

• Position the crosshead so that fixtures cannot touch each other when the

actuator is fully extended. This may not always be feasible at all times, but it
should be practiced whenever possible.

• Use force limits. Force limits can help in some instances but might not stop

the actuator fast enough in all situations.

• Ensure that you have selected the correct calibration for the transducer being

used. Also ensure that the system tuning has been optimized for the
transducer being used.

Series 322 Load Unit Operation

51

322 Load Unit: Control Module

Unclamp Clamp

Upper

Lower

Grip

Grip

Pressure

1

2

3

The controls for the load unit are located on a module mounted to the front of the
load unit. For some configurations, the grip controls and lift and lock controls
might be on separate control modules.

Load Unit Controls (part 1 of 2)

C

ONTROL DESCRIPTION

Hydraulic Grip Controls

Controls the optional hydraulic grips. Hydraulic grips let you quickly and
easily install and remove specimens. The left handle controls the lower grip
and the right handle controls the upper grip.

Pressure

Adjusts the amount of hydraulic pressure to the grips. The adjustment range is
1–21 MPa (100–3000 psi) or 1–69 MPa (100–10,000 psi). The highest
pressure setting depends on the maximum pressure setting. Adjust the control
clockwise to increase the hydraulic pressure. Use the pressure gage to measure
the clamping force.

Operation

52

Series 322 Load Unit

Load Unit Controls (part 2 of 2)

Rate

Up

Stop

Down

Unlock Lock

C

ONTROL DESCRIPTION

Rate

Crosshead Lift/Lock
Controls

Emergency Stop

Adjusts how fast the grips clamp and unclamp.

Adjust the control clockwise to slow the clamping of the specimen.

Controls the movement and clamping of the crosshead. The left handle raises
and lowers the crosshead. The right handle locks and unlocks the crosshead.
The crosshead must not be moved while it is clamped.

Shuts down the hydraulic pressure and stops the test program. Press this button
to shut down hydraulic power, and twist the switch clockwise to release it. Use
the Emergency Stop button to shut down your test if something unexpected
should happen.

Series 322 Load Unit Operation

53

322 Load Unit: Crush Point Hazards

Crush
point
areas

It is important to stay clear of any potential crush points when the system is
operating. Know where the crush points are in your system and protect yourself
and others from those crush points with appropriate safety devices. The
following paragraphs describe crush points and precautions to take while
working around crush points.

Locations A crush point exists between the platen and crosshead on load units where the

actuator piston rod and specimen move (both areas are shown). Another potential
crush point exists where the lower end of the actuator piston rod extends below
the platen and the bottom of the load unit/load frame.

Precautions Keep clear of any mechanical linkage that moves within a closed area. If the

linkage should move (when the system starts or due to mechanical failure), very
high forces can be present that could pinch, cut, or crush anything in the path of
linkage movement.

Never allow any part of your body to enter the path of machine movement or to
touch moving machinery, linkages, hoses, cables, specimens, etc. These present
serious crush points or pinch points.

Load Unit: Specimen Installation

The procedure to install a specimen varies due to the variety of test fixtures,
grips, and the type of specimen being installed. This section should be considered
a guideline. You need to modify this procedure to suit your equipment.

Prerequisite You must have the necessary grips and/or fixturing installed. You must also have

the controller set up to control the actuator movement, and you must have a test
program defined.

54

Operation

Series 322 Load Unit

When changing hydraulic grips, make sure you cap or plug the hydraulic

CAUTION

WARNING

CAUTION

hoses when removed to prevent oil spillage.

Oil spillage can create an environmental concern and slippery surface that can
cause personal injury. Promptly clean up any oil that might have spilled when
hoses were removed.

The crosshead is very heavy.

A dropping crosshead can crush hands, damage grips, and smash
specimens.

Be careful when working in a crush zone. To reduce the hazards in this procedure,
observe the following:

• Ensure to set and enable displacement interlocks to limit the actuator’s

movement.

• Ensure that the crosshead is locked.

• Ensure that the columns are clean and dry.

• Keep your hands out of the crush zone except when performing the steps

needed to complete this procedure.

1. Prepare the components for specimen installation.

A. Ensure that the crosshead is locked.

B. Turn on system electrical power.

C. Turn on high hydraulic pressure.

D. Use your controller to move the actuator to its start position (usually

mid-displacement). The starting position of the actuator depends on the
type of fixtures, grips, and the test being set up.

The crosshead can slowly drift down the columns if the locks are turned off
and when hydraulic pressure is turned off.

The crosshead can damage any test fixtures, grips, and specimen in its
path.

Unlock the crosshead only to reposition it. Always lock the crosshead after you
have repositioned it, and never leave the crosshead unlocked.

Series 322 Load Unit Operation

55

2. Set the crosshead position.

CAUTION

The crosshead position depends on the length of the specimen being tested,
the starting position of the actuator, and the size of the fixtures or grips
being used.

3. Install the specimen.

Specimen installation varies according to the type of grip being used. See
the appropriate grip manual for installation instructions. MTS manufactures
a variety of grips:

• The Series 641 Hydraulic Wedge Grips (hydraulically controlled) are

specifically designed for static or fatigue testing applications. They are
available with a self aligning feature. These are hydraulically
controlled grips.

• The Series 643.6X Tension/Compression Grips (mechanical) are used

for testing threaded-end and button-end specimens in tension,
compression, or tension/compression.

• The Series 646 Hydraulic Collet Grips (hydraulically controlled) are

designed to perform in a wide variety of testing applications (for
example, high and low cycle fatigue, tension, and compression).

• The Series 647 Hydraulic Wedge Grips (hydraulically controlled) are

specifically designed for static or fatigue testing applications. There are
a variety of configurations of this grip.

• The Series Advantage Wedge Grips are specifically designed for static

or fatigue testing applications. These are a mechanical version of the
Series 647 Hydraulic Wedge Grips.

• Specialty grips (mechanical) are designed to grip specific types of

material such as string, tread, tendons, etc.

Each type of grip requires the specimen or specimen fixture to fit properly
into the grip. You should always review specimen installation procedures
found in any grip product information manual.

Before testing, ensure both grips are clamped and the specimen is secure.

An insufficiently gripped specimen can cause specimen damage, equipment
damage and the possibility of specimen fragmentation.

56

Operation

Series 322 Load Unit

Load Unit: Position the Crosshead Hydraulically

1. This step pressurizes the lift actuators. The crosshead might have shifted
position while hydraulic pressure was turned off.

Briefly turn the Crosshead Lift/Lock Controls to the lift crosshead
position to apply a slight upward pressure to the crosshead.

Then return the lift control to the stop position.

2. Use the Crosshead Lift/Lock Controls to unclamp the crosshead.

Wait 30 seconds for the pressure in the crosshead locks to drop to zero.

Note Always lower the crosshead to where you want it. The pressure

remaining in the lift cylinders after raising the crosshead can slightly shift
its alignment. Lowering the crosshead to its final position removes this
pressure and improves alignment.

3. Use the Crosshead Lift/Lock Controls to move the crosshead to a point
where you can install the specimen (or specimen fixture) into the upper grip
or fixture without obstruction.

Set the control to the stop position “O” before proceeding.

4. Use the Crosshead Lift/Lock Controls to clamp the crosshead to its current
position.

Wait 30 seconds for the locks to fully clamp the columns.

Series 322 Load Unit Operation

57

Load Unit: Position the Crosshead Manually

WARNING

This procedure describes how to position a crosshead for a load unit with no
hydraulic crosshead lifts or locks.

The crosshead is very heavy.

A dropping crosshead can crush hands, damage grips, and smash
specimens.

Observe the following precautions to reduce the possibility of unexpected
crosshead movement:

• Ensure that the crosshead is locked.

• The overhead crane and lifting chains must be able to support the weight of

the crosshead (see the Crosshead Weight table below).

• Center the crane directly over the load unit.

• Remove any slack in the lifting chains before unlocking the crosshead.

• Completely loosen all crosshead locking bolts before attempting to move the

crosshead.

• Keep the columns clean and dry. The crosshead cannot be securely clamped

to greasy or damp columns.

The following procedure describes using an overhead crane to position the
crosshead. You can use any device that can lift the weight of the load unit.

Frame Rating 100 kN (22 kip) 250 kN (55 kip) 500 kN (110 kip)

Crosshead Weight 57 kg (125 lb) 102 kg (225 lb) 193 kg (425 lb)

1. Center the overhead crane directly over the load unit.

2. Attach the lifting chains to the lifting rings. Remove any slack in the lifting
chains while keeping chain tension to a minimum.

3. Remove the covers on the ends of the crosshead. The crosshead covers must
be removed to access the manual locking bolts and to clean and lubricate the
bolts. Six 1/4-20 screws (three top, three bottom) on each cover need 5/32
hex (not included). Hand-tighten when reinstalling the covers.

58

Operation

Series 322 Load Unit

4. Loosen the crosshead locking bolts in 1/4 turn steps (counterclockwise).

Load Unit Rating 100 kN (22 kip)

190 N·m (140 lbf·ft)

Load Unit Rating 250 kN (55 kip)

271 N·m (200 lbf·ft)

Load Unit Rating 500 kN (110 kip)

Rear

271 N·m (200 lbf·ft)

Load Unit Rating 500 kN (110 kip)

Front

271 N·m (200 lbf·ft)

The following figure shows the sequence of loosening the crosshead bolts.

Manually clamping the

crosshead

Series 322 Load Unit Operation

5. Raise or lower the crosshead using the overhead crane.

6. Manually claim the crosshead to lock the crosshead into position.

The manual clamping procedure is a four step process. The four steps allow the
crosshead to be clamped evenly.

59

The crosshead is very heavy.

WARNING

CAUTION

A dropping crosshead can crush hands, damage grips, and smash
specimens.

Observe the following precautions to reduce the possibility of unexpected
crosshead movement:

• Ensure that the crosshead is locked.

• The overhead crane and lifting chains must be able to support the weight of

the crosshead (see the Crosshead Weight table below).

• Center the crane directly over the load unit.

• Remove any slack in the lifting chains before unlocking the crosshead.

• Completely loosen all crosshead locking bolts before attempting to move the

crosshead.

• Keep the columns clean and dry. The crosshead cannot be securely clamped

to greasy or damp columns.

Prerequisite Before clamping the crosshead in place, you must have determined the proper

crosshead position and moved the crosshead to that position.

The crosshead can slowly drift down the columns if the locks are turned off
and when hydraulic pressure is turned off.

The crosshead can damage any test fixtures, grips, and specimen in its
path.

Unlock the crosshead only to reposition it. Always lock the crosshead after you
have repositioned it, and never leave the crosshead unlocked.

Procedure Tighten the crosshead clamping bolts according to the torque settings shown in

the following table. Torque the crosshead bolts to the values in Step 1 and so on
until Step 4 is complete. Use the same sequence as when you loosened the bolts.

LOAD UNIT STEP 1STEP 2STEP 3

100 kN

(22 kip)

250 kN

(55 kip)

500 kN

(110 kip)

20 N·mm
(15 lbf·ft)

20 N·m
(15 lbf·ft)

20 N·m
(15 lbf·ft)

171 N·m
(126 lbf·ft)

244 N·m
(180 lbf·ft)

244 N·m
(180 lbf·ft)

190 N·m
(140 lbf·ft)

271 N·m
(200 lbf·ft)

271 N·m
(200 lbf·ft)

*

TEP 4

S

190 N·m
(140 lbf·ft)

271 N·m
(200 lbf·ft)

271 N·m
(200 lbf·ft)

60

Operation

* This step ensures uniform tightness.

Series 322 Load Unit

Load Unit: Adjust the Grips’ Clamp Rate

Rate

Faster

Slower

WARNING

Clamp Unclamp

The clamp rate determines how fast the grip can clamp a specimen.

1. Ensure that both the upper grip control and lower grip control are in the
unclamp position.

2. Turn on electrical power at the test controller.

3. Turn on low or high hydraulic pressure.

4. If needed, move the crosshead or actuator so that the dummy specimen can
be easily installed in the lower grip.

5. Turn the Rate control fully clockwise for the slowest clamp speed.

The crosshead is very heavy.

A dropping crosshead can crush hands, damage grips, and smash
specimens.

Be careful when working in a crush zone. Observe the following to reduce the
hazards in this procedure:

• Ensure to set and enable displacement interlocks to limit the actuator’s

movement.

• Ensure that the crosshead is locked.

• Ensure that the columns are clean and dry.

• Keep your hands out of the crush zone except when performing the steps

needed to complete this procedure.

6. Fully install the dummy specimen in the lower grip.

7. Cycle the lower grip control between the clamp and unclamp positions to
clamp and unclamp the specimen.

Series 322 Load Unit Operation

61

A. Watch the speed at which the lower grip clamps and unclamps the

CAUTION

specimen.

B. Adjust the Rate control counterclockwise for the desired speed.

Load Unit: Adjust the Grips’ Clamp Force

The Pressure control adjusts the hydraulic pressure applied to the grips. The
Rate control adjusts the grips’ clamping speed. They must be adjusted before the

grips can be used.

The amount of hydraulic pressure applied depends on the type of grips you are
using and what you are gripping. Use your grip manual to determine the correct
hydraulic pressure before adjusting the force. Experiment with a dummy
specimen to find the best setting.

Note The Pressure control can adjust the grip pressure up to the maximum

output pressure setting (which is initially set by MTS Systems
Corporation).

1. Ensure that both the upper grip control and lower grip control are in the
unclamp position.

2. Turn on the electrical power at the test controller.

3. Turn on low or high hydraulic pressure.

4. If needed, move the crosshead or actuator so that the dummy specimen can
be easily installed in the lower grip.

Grips are designed to operate within a range of hydraulic pressure.

Too much pressure can damage both the grips and the specimen.

Do not adjust grip pressure higher than the grip rating. See your grip manual to
determine the correct hydraulic pressure to apply to your grips before adjusting
the Pressure control.

62

Operation

Series 322 Load Unit

5. Adjust the Pressure control for the desired hydraulic pressure.

Pressure

Less

More

6. If you exceed the desired pressure setting, adjust the Pressure control
counterclockwise 1/2 turn. If pressure setting exceeds 20 MPa (3000 psi)
cycle (clamp and unclamp) one of the grips. Return to Step 5.

Series 322 Load Unit Operation

63

64

Operation

Series 322 Load Unit

Maintenance

322 Load Unit: Maintenance Intervals 66

Load Unit: Daily Inspections 67

Load Unit: Clean the Columns 67

Load Unit: Prevent Rust 68

Load Unit: Bleed the Hydraulic Lift Cylinders 69

Load Unit: Adjust the Hydraulic Locks 71

Load Unit: Lubricate the Crosshead Locking Bolts 74

Load Unit: Align the Force Transducer 75

111 Accumulator: Maintenance Overview 81

111 Accumulator: Check and Change Precharge Pressure 83

244 Actuator: Maintenance 86

298 HSM: Maintenance 86

252 Servovalve: Maintenance Overview 88

252 Servovalve: Replace the Filter Element 88

252 Servovalve: Adjust the Mechanical Null 90

Series 322 Load Unit Maintenance

65

322 Load Unit: Maintenance Intervals

The following table lists the recommended interval for each of these procedures.

HAT TO DO WHEN TO DO IT

W

Make daily inspections

Clean the load unit columns

Prevent rust

Bleed the hydraulic lift cylinders

Adjust the hydraulic locks

Lubricate the Crosshead
Locking Bolts

Lubricate the crosshead locking
bolts

Align the force transducer

Before the start of each day’s
testing.

When the columns become greasy
or dirty.

Depends on the operating
environment; more often in humid
environments.

When the crosshead begins to
move roughly; if the sealed side of
the hydraulic supply is opened to
air.

When the crosshead sticks or
moves jerkily on the column.

Whenever they begin to be hard to
tighten or sticky when loosened.

When the bolts begin to loosen or
tighten stiffly (manual locking
crossheads only).

After actuator or force transducer
installation; when a better
alignment between the two is
desired.

66

Maintenance

Check the accumulators’
precharge pressures. Adjust if
necessary

Clean exposed actuator piston
rod

Change 298 HSM filter.

Perform 252 Servovalve
maintenance: change filter.

Perform 252 Servovalve
maintenance: adjust mechanical
null.

At least once a month; more often
as required by operating
conditions.

Weekly; more often as required by
operating conditions.

When indicator is in bypass
position or when hydraulic fluid is
changed.

When servovalve performance has
deteriorated.

After the valve balancing
procedure (electrical
compensation) has been completed
and the results are judged
unsatisfactory.

Series 322 Load Unit

Load Unit: Daily Inspections

WARNING

Before the start of each day’s testing, do a quick inspection of your load unit.
Following are typical things that should be checked daily:

• Ensure that there are no leaks from lifts or locks.

• Ensure that there are no leaks from the actuator, hydraulic service manifold,

servovalve, or accumulators.

• Ensure that electrical connections are tight, with no frayed or poorly routed

cables.

• Ensure that hoses are routed properly and fittings are not leaking.

Load Unit: Clean the Columns

The crosshead locks can not securely clamp the crosshead to dirty or greasy
columns. You will need Ethanol and lint-free cloths to perform this procedure.

The crosshead can slide down the columns.

Crosshead cleaning takes place in a crush zone where pinched fingers and
crushed hands can occur.

Do not position yourself in a crush zone. Always lock the crosshead after moving
it. Always turn off hydraulic pressure before cleaning the columns. Wait two
minutes for pressure to bleed off before starting work.

1. Ensure that the crosshead is locked.

2. Using a clean, lint-free cloth, clean the exposed surfaces of the columns
with Ethanol.

3. If your load unit does not have hydraulic crosshead lifts, skip ahead to the
next step. If your load unit has hydraulic crosshead lifts, complete the
following steps:

A. Turn on system electrical power.

B. Apply high hydraulic pressure to the load unit.

4. If there is a specimen in the load unit, remove it.

5. Unlock and move the crosshead to expose the uncleaned section of the
columns.

6. Lock the crosshead.

7. If hydraulic pressure has been turned on, turn it off. Wait two minutes for the
pressure to bleed off before going on to the next step.

8. Clean the remaining sections of the columns.

Series 322 Load Unit Maintenance

67

Load Unit: Prevent Rust

WARNING

Unpainted surfaces: Spray with silicone, and
then wipe with a clean, lint-free cloth. Or,
wipe with a clean, lint-free cloth dampened
with clean hydraulic fluid.

Chrome plated surfaces: For microscratches,
wipe with a clean, lint-free cloth dampened
with Ethanol. For rust discoloration, polish
with a very fine emery cloth, and then wipe
down.

Black oxide surfaces: Spray with silicone, and
then wipe with a clean, lint-free cloth. Or, wipe
with a clean, lint-free cloth dampened with
clean hydraulic fluid.

Painted surfaces: For small scratches, use
touchup paint. For large scratches, sand,
prime, and use touchup paint.

Note: 318 Load Unit shown for reference.

Where you operate the load unit determines how often you take rust prevention
measures. Humid and corrosive environments require more prevention.

Recommended

supplies:

• Ethanol

• Silicone spray

• 000 emery cloth

• Touchup paint

• Metal primer paint

• Lint-free cloths

The crosshead can slip if the columns are still damp with kerosene.

You can be hurt and your equipment damaged.

The crosshead locks cannot securely clamp on damp columns. Wait until the
columns are dry to the touch before moving and locking the crosshead.

Maintenance

68

Series 322 Load Unit

Load Unit: Bleed the Hydraulic Lift Cylinders

Bleed ports

CAUTION

Bleed both hydraulic lift cylinders whenever the crosshead does not move
smoothly. Also bleed them whenever the sealed side of the hydraulic system has
been opened to air. The following figure shows the location of the bleed ports for
the two types of lifts commonly used.

The crosshead can slowly drift down the columns if the locks are turned off
and the hydraulic pressure is turned off.

The crosshead can damage any test fixtures, grips, and specimen in its
path.

Unlock the crosshead only to reposition it. Always lock the crosshead after you
have repositioned it, and never leave the crosshead unlocked.

1. Make sure your crosshead is locked.

2. Turn on system electrical power.

3. Reset any active interlocks at the test controller.

4. Turn on high hydraulic pressure.

Series 322 Load Unit Maintenance

69

5. If there is a specimen in the load unit, remove it.

WARNING

1/2 turn maximum

Close

No bubbles

The lifts contain hydraulic fluid under high pressure.

If the bleed port screw is unscrewed all the way, the screw can fly out of its
port at high velocity and it could hurt you or damage your equipment.

Unscrew the bleed port screw no more than 1/2 turn to vent the trapped air.

Open to Bleed

6. Use a 1/8 inch hex key (or slotted screwdriver, depending on model number)
to open one of the bleed ports. Do not unscrew the bleed port screw more
than 1/2 turn.

7. Briefly turn the Lift Control to the lift crosshead position to pressurize the
lift cylinders. Then return it to the stop crosshead position.

8. Shut the bleed port when bubble-free fluid begins oozing out. If necessary,
again pressurize the lift cylinders to force all the air out.

9. Repeat Step 6 through Step 8 to bleed the air out of the other lift cylinder.

70

Maintenance

Note If fluid continues to leak out of a shut bleed port, turn off hydraulic

pressure to the load unit. Let the pressure in the lift cylinders return to
zero. Then replace both bleed port screws (MTS par number
010-037-601).

Series 322 Load Unit

10. Turn on high hydraulic pressure. If pressure was reduced at the hydraulic

CAUTION

power unit, restore full pressure.

11. Briefly turn the Lift Control to the lift crosshead position to pressurize the
lift cylinders. Then return it to the stop crosshead position.

12. Unlock the crosshead and exercise the crosshead. Then return to the stop
crosshead position. Raise and lower the crosshead to check for smooth
operation. Lock the crosshead.

13. If the crosshead does not move smoothly, go back to Step 4 and continue
from there.

Load Unit: Adjust the Hydraulic Locks

Hydraulic locks might need adjustment if the crosshead still moves jerkily after
bleeding the lift cylinders. Adjustment might also be needed if the crosshead
slips under full load.

If adjusting the hydraulic locks does not fix these problems, call MTS.

1. Turn on electrical power at the controller. Do not turn on hydraulic pressure
yet.

2. If the crosshead is already at a comfortable working level with no specimen
installed, proceed to Step 3.

If not, position the crosshead for a comfortable working level. Proceed as
follows:

A. Reset any active interlocks at the test controller.

B. Turn on high hydraulic pressure.

C. If there is a specimen in the load unit, remove it.

D. Move the crosshead to a comfortable working height.

The crosshead can slowly drift down the columns if the locks are turned off
and the hydraulic pressure is turned off.

The crosshead can damage any test fixtures, grips, and specimen in its
path.

Unlock the crosshead only to reposition it. Always lock the crosshead after you
have repositioned it, and never leave the crosshead unlocked.

3. Remove the covers on the ends of the crosshead. The crosshead covers must
be removed to adjust the hydraulic locks. Four 1/4-20 screws (two top, two
bottom) on each cover need 5/21 hex (not included). Hand-tighten when
reinstalling the covers.

Series 322 Load Unit Maintenance

71

4. Use the Lock Control to lock the crosshead. Then torque the manual

3

4

1

2

3

4

11

2

1

2

Load Unit Rating 100 kN (22 kip)

100 N·m (140 lbf·ft)

Load Unit Rating 250 kN (55 kip)

271 N·m (200 lbf·ft)

Load Unit Rating 500 kN (110 kip)

271 N·m (200 lbf·ft)

crosshead locking bolts in the order shown in the following illustration.

5. Turn off hydraulic pressure.

6. Use the Lock Control to the unlock crosshead position to remove pressure
from the hydraulic locks. Wait two minutes for the pressure in the locks to
drop to zero before going on to the next step.

72

Maintenance

Series 322 Load Unit

7. Tighten each lock’s cap screw until its piston bottoms out. Then loosen and

Tighten

Bottom out
position

Loosen, then
hand tighten

Loosen1/4 turn

hand-tighten each cap screw.

8. Loosen each of the hydraulic locks’ cap screws 1/4 turn.

9. Turn on electrical power at the test controller if you have not already done
so.

10. Reset any active interlocks at the test controller.

11. Turn on high hydraulic pressure.

12. Return the Lock Control to the lock crosshead position to pressurize the
hydraulic locks.

13. Fully loosen the manual crosshead locking bolts. Then turn the Lock
Control to the unlock crosshead position.

14. Move the crosshead, locking and unlocking it, to check for smooth

Series 322 Load Unit Maintenance

operation.

73

Load Unit: Lubricate the Crosshead Locking Bolts

Unscrew one
at a time

Clean and
lubricate

Lubricate the locking bolts in a manually locked crosshead whenever they begin
to be hard to tighten or sticky when loosened.

1. Remove the covers on the ends of the crosshead. The crosshead covers must
be removed to lubricate the crosshead locking bolts. Four 1/4-20 screws
(two top, two bottom) on each cover need 5/21 hex (not included). Hand
tighten when reinstalling the covers.

2. Position the crosshead at a comfortable working height.

3. Lock the crosshead following your normal crosshead locking procedure.

4. Remove a single locking bolt.

5. Clean the bolt threads with a stiff nylon brush. Use degreaser if necessary.
Dry the threads.

Then lightly lubricate the threads with Molykote G-n paste.

6. Reinstall the locking bolt, tightening it to a value specified in the following
table.

L

OAD UNIT RATING TORQUE

100 kN (22 kip) 190 N·m (140 lbf·ft)

250 kN (55 kip) 271 N·m (200 lbf·ft)

500 kN (110 kip) 271 N·m (200 lbf·ft)

7. Repeat Steps 4, 5, and 6 until all the bolts have been lubricated.

74

Maintenance

Series 322 Load Unit

Load Unit: Align the Force Transducer

The identification plate specifies the final torque value.

Identification
plate

Stud

Hex nut

Washer

Adapter bushing

Transducer
(appearance
can vary)

Crosshead

Identification plate

Washer

Preloaded collar

Stud

This section describes how to align a force transducer with the load unit actuator.
The load units shown may vary from what you may have.

Load units can come with two types of transducer mounting hardware. One
preloads the force transducer with a hex nut; the other uses a preloader collar
with jackbolts or captive set screws. Some load units use a preloader collar with
six or eight internal jackbolts to preload the force transducer.

Required equipment • Torque wrench with a 5–135 N·m (5–100 lbf·ft) range

• Molykote G·n paste

• Rubber mallet

• 0.0025 mm (0.0001 in) precision dial indicator with a magnetic base

Hex Nut Preloading Hardware Preloader Collar Hardware

Series 322 Load Unit Maintenance

1. Get things ready.

A. If grips are installed, remove them.

B. Turn on system electrical power.

C. Turn on high hydraulic pressure.

2. Set up the load unit.

A. Position the actuator at midstroke.

75

B. Set and enable the test controller’s upper and lower limit detect

WARNING

Unscrew/Tighten

interlocks to limit the actuator’s movement to 2 mm (0.10 in) in each
direction.

C. Move the crosshead so there is about 360 mm (14 in) between the top

of the actuator and the bottom of the force transducer.

D. Lock the crosshead.

Alignment takes place in a crush zone with hydraulic pressure on.

Hands can be crushed and equipment can be damaged equipment when
hydraulics are turned on. Be careful when working in a crush zone.

Observe the following to reduce the hazards in this procedure:

• Ensure that you set and enable displacement interlocks to limit the actuator’s

movement.

• Ensure that the crosshead is locked.

• Reduce the load unit’s hydraulic pressure to low.

• Keep your hands out of the crush zone except when performing the steps

needed to complete this procedure.

E. Turn the load unit’s hydraulic pressure to high.

F. If your load unit has an antirotate actuator, unscrew the four cap screws

that attach the antirotate plate to the bottom of the piston. The antirotate
plate is at the bottom of the actuator, inside the base of the load unit.

76

Maintenance

Series 322 Load Unit

3. Check the alignment.

360° 360°

Read
along
the edge

Read
along
the edge

Zero

Zero

In this step, you check the alignment between the force transducer and the
actuator.

.

Attaching and Zeroing the Indicator

A. Attach the dial indicator to the actuator.

On a low profile force transducer, adjust the indicator to take the
reading along the edge of the loading surface.

On cylindrical style force transducers, adjust the indicator so that its
stylus just touches the polished bottom edge of the transducer.

B. Zero the indicator.

C. Slowly turn the actuator to rotate the indicator 360° around the force

transducer.

Stop frequently to take indicator readings. Keep your hands off the
actuator and indicator when taking the readings. Compute the total
indicator runout (TIR). Take the maximum dial indicator reading and
subtract the minimum dial indicator reading.

L

OAD UNIT RATING TIR

250 kN (55 kip) or less >0.038 mm (0.0015 in)

500 kN (100 kip) 0.051 mm (0.0020 in)

D. If the TIR is 0.038 mm (0.0015 in) or less, the force transducer is

accurately aligned with the actuator. Go to Step 6.

If the TIR is greater than 0.038 mm (0.0015 in), the force transducer
needs to be aligned with the actuator. Start over with Step 3.

Series 322 Load Unit Maintenance

77

4. Prepare the force transducer.

Tighten

G-n paste

Wooden
blocks

Depending on the type of force transducer you have, perform one of the
following procedures:

• Hex nut mount only

• Preloader collar mount only

Hex nut mount only The following procedure applies only to force transducers that are mounted

to the crosshead with a single hex nut.

A. Put blocks of wood between the actuator and the force transducer. They

will support the force transducer when its mounting nut is loosened.

B. Loosen the mounting nut. Lubricate the exposed stud threads and

washer with Molykote G·n paste.

C. Tighten the mounting nut just enough to pull the force transducer

firmly against the crosshead.

D. Remove the wood blocks. Reinstall and zero the indicator.

78

Maintenance

Lubricating the Hex Nut

Series 322 Load Unit

Preloader collar mount

1

6

4

2

5

3

Remove, one at a time

G-n paste

only

The following procedure applies only to force transducers that are mounted
to the crosshead using a preload collar.

Loosen the six jack bolts or setscrews in 1/4 turn steps to remove most of the
tension on the preloader collar, following a standard crisscross torque
sequence.

• If your preloader collar has jackbolts, remove and lubricate them one at

a time. Lubricate the washer underneath the jackbolt. After you
reinstall the jackbolt, tighten it enough to keep the force transducer
pulled firmly against the crosshead.

• If your preloader collar has captive setscrews, unscrew them one at a

time. Lubricate the washer underneath the setscrew. Then retighten the
setscrew just enough to keep the force transducer pulled firmly against
the crosshead.

Preloader Collar Bolts

5. Align the force transducer.

This step describes how to align a force transducer to the crosshead.

A. Lightly tap the transducer with the rubber mallet to change its position

until you get a TIR of 0.038 mm (0.0015 in) or less.

Series 322 Load Unit Maintenance

79

B. Tighten to 5% of the torque recorded on the identification plate.

1

6

4

2

5

3

1

2

3

4

5

6

7

8

Hex nut—Tighten the nut to 5% of the final torque shown on the
identification plate.

Preloader collar—Tighten the jackbolts or setscrews to 5% of the
final torque shown on the identification plate.

C. Rotate the indicator to see if the TIR is still 0.038 mm (0.0015 in) or

less. If not, loosen the nut or preloader collar and return to Step 4.
(Loosen the preloader collar following the sequence shown below.)

D. Repeat Steps B and C to tighten the force transducer for the following

torque progression: 50%, 75%, and 100%.

80

Maintenance

Bolt Torque Sequence

E. Preloader collar only—For uniform tightness, retorque the jackbolts

or setscrews to 100% of the final torque shown on the identification
plate.

6. Finish the procedure.

In this step, you complete the force transducer alignment procedure.

A. Remove the dial indicator.

B. If you reduced pressure at the hydraulic power unit, restore full

hydraulic pressure.

Series 322 Load Unit

C. Turn the load unit’s hydraulic pressure to off.

Unscrew/Tighten

Anti-Rotate Actuator—Tightening the Cap Screws

D. If your load unit has an antirotate actuator, tighten the four antirotate

cap screws to a torque listed in the following table. (The actuator force
rating is stated on an identification plate at the rear of the load unit.)

A

CTUATOR FORCE RATING TORQUE RATING

25 kN (5.5 kip) 3.7 N·m (2.7 lbf·ft)

50–500 kN (11–110 kip) 48 N·m (35 lb·ft)

111 Accumulator: Maintenance Overview

Maintaining the proper pressure level for your accumulators is essential for
optimum system performance and component life. Review the following figure
to familiarize yourself with the accumulator components and their locations.
Also review the following guidelines before performing any procedure.

Series 322 Load Unit Maintenance

81

Degrees Celsius:

current pressure original pressure

273 current temperatrure()+
273 original temperature()+

---------------------------------------------------------------------





×=

current pressure original pressure

460 current temperatrure()+
460 original temperature()+

---------------------------------------------------------------------





×=

Degrees Fahrenheit:

Use the following guidelines to determine when maintenance is required.

• Check the precharge pressure at periodic intervals. The length of time

between checks depends on how the system is used. Some factors to
consider when establishing this time interval are operating frequency,
displacement, and duration. Start with one month intervals until you
determine another interval is more appropriate.

• Maintain a log book on the condition of the precharge at each check. Use

this data to determine if the time between checks should be increased or
decreased and if maintenance is required.

• Because the precharge pressure level varies with a temperature change, the

level should always be checked at the same temperature. If it is not, use one
of the following formulas to determine if the precharge level is acceptable.

• If a pressure line accumulator has a pressure level change of ±1.4 MPa (200

psi) between checks, the accumulator requires maintenance or the time
interval between checks needs to be shortened.

• If a return line accumulator has a change of ±50% of the original pressure

level between checks, the accumulator requires maintenance or the time
interval between checks needs to be shortened.

• If the precharge pressure level increases at each check interval, this indicates

that fluid is collecting on the gas side (a small amount of fluid leakage is
normal). When the precharge pressure level cannot be maintained within the
limits, remove the fluid and charge the accumulator. If the levels are again
exceeded at the first check interval, replace the piston seals after the initial
fluid has been changed.

• If the precharge pressure level decreases at each check interval, this

indicates gas leakage to the fluid side. When the precharge pressure level
cannot be maintained within the limits stated in the previous guidelines,
replace the accumulator piston seals.

• During normal operation, the accumulator piston should be near the center

of the accumulator cylinder. To check the approximate piston location, note
the warm-to-hot transition point on the accumulator cylinder wall during
operation. If the piston is near the charging stem end, the accumulator may
need charging. If the piston is at the other end, the accumulator may have an
excess charge, or more likely an excessive amount of hydraulic fluid has
collected in the gas chamber.

Maintenance

82

Series 322 Load Unit

111 Accumulator: Check and Change Precharge Pressure

WARNING

Special equipment An accumulator charging kit (MTS part number 376986-01) is for any Series 111

Accumulator:

Prerequisite To prepare the accumulator for precharge check:

Accumulators are pressurized devices.

Pressurized accumulators and their parts can become lethal projectiles if
disassembled and can cause death to persons and/or damage to
equipment.

Do not remove an accumulator that is pressurized. Completely remove hydraulic
pressure and discharge the accumulator before any parts, except the protective
cover and valve stem cap, are removed.

1. Ensure that system hydraulic pressure has been reduced to zero before
proceeding. To do this, turn off the hydraulic power unit and exercise the
actuator until it stops moving.

2. Close the bleed valve on the accumulator charging kit. Remove the
protective cover and valve stem cap from the accumulator.

Check the precharge

pressure

1. Connect the charging kit chuck valve to the accumulator valve stem.

Series 322 Load Unit Maintenance

83

2. With an open-end wrench, turn the locknut counterclockwise on the

WARNING

accumulator valve assembly to open the valve. Read the pressure on either
the high or low accumulator charging kit pressure gage.

• If the pressure reading is other than the required pressure level recorded on

the accumulator, continue with the next subsection, “Change the Precharge
Pressure”.

• If the pressure level corresponds to the level recorded on the accumulator

label, turn the locknut clockwise to close the valve and continue this
procedure.

3. Open the bleed valve on the accumulator charging kit and remove the chuck
valve from the accumulator. Replace the valve stem cap and protective
cover on the accumulator.

Change the Precharge

Pressure

Often the precharge of an accumulator mounted on a hydraulic supply line is
increased to enhance system performance and reduce the transient HPS flow
demands. Accumulators may be precharged to 10 MPa (1500 psi) or more,
although amounts above 14 MPa (2200 psi) will have less and less performance
effect in most situations. Be sure that you read the following warning before you
charge your accumulator.

Accumulators have specific pressure ratings.

If the precharge pressure is too high, the accumulator can bottom out
causing the release of metal particles into the hydraulic fluid. Charging
accumulators above their rated level can damage system equipment.

Do not charge accumulators to pressures above their rated level. Charge
accumulators below their rated fatigue pressure of 21 MPa (3000 psi) for the
Model 111.11B and 22 MPa (3200 psi) for the Model 111.12C. Use a suitable
regulator and gage set to an accumulator’s charges.

Decreasing pressure To decrease the precharge pressure:

1. Slowly open the bleed valve on the accumulator charging kit until gas
begins to escape. When the pressure reading on the appropriate pressure
gage drops to the level required, close the bleed valve.

2. Close the locknut (or close the chuck valve if you have a core-type valve).
Open the bleed valve on the accumulator charging kit and remove the chuck
valve from the accumulator.

3. Install the valve stem cap and protective cover.

Increasing pressure To increase the precharge pressure:

1. Close the locknut on the accumulator (or close the chuck valve for a core­type valve).

2. Open the bleed valve two turns.

Maintenance

84

Series 322 Load Unit

Mixing gases can produce unpredictable results.

WARNING

CAUTION

Do not use another gas to precharge an accumulator. Use only dry nitrogen gas to
precharge accumulators.

3. Connect the nitrogen supply hose from the supply bottle pressure regulator
output to the input check valve on the charging kit.

4. Open the nitrogen bottle valve. Check the nitrogen bottle pressure gage on
the regulator. (The bottle must contain sufficient pressure to provide an
adequate gas volume.)

5. Monitor the regulator output pressure gage and adjust the regulator output
pressure valve to the required level.

Rapid flow rates with pressure differentials of more than 2.1 MPa (300 psi)
across the input check valve can damage the valve seal(s).

Avoid rapid and extreme pressure transitions.

Do not allow rapid flow rates. Open the regulator shut-off valve only far enough to
permit a gradual transfer of gas.

6. Slowly open the regulator shut-off valve until gas is heard escaping from the
accumulator charging kit bleed valve. Allow gas to slowly escape for
approximately ten seconds, then close the bleed valve. Immediately close
the regulator shut-off valve before the pressure reading on either the high or
low charging kit pressure gage exceeds the pressure level of the
accumulator.

7. Open the locknut (or open the chuck valve for a core-type valve). Slowly
open the regulator shut-off valve until the pressure indicator on either the
high or low charging kit pressure gage begins to rise. When the pressure is at
the required pressure level (recorded on the accumulator), close the
regulator shut-off valve.

8. Close the locknut (or close the chuck valve for a core type valve).

9. Open the bleed valve on the accumulator charging kit and remove the chuck
valve from the accumulator.

10. Install the valve stem cap and protective cover. Close the valve on the
nitrogen bottle.

Series 322 Load Unit Maintenance

85

244 Actuator: Maintenance

Pressure
Accumulator

Return
Accumulator

Inlet
Filter

Dirty
Filter
Indicator

The series 244 Actuator is designed for extended periods of operation without
extensive maintenance requirements.

A summary of the routine maintenance procedures is listed below:

Weekly Clean exposed areas of the actuator piston rod with a clean, dry, lint free rag. If

the actuator is continually exposed to a dirty operating environment, clean the
piston rod on a daily basis.

Monthly Inspect actuator piston rod and seals for excessive wear and/or leakage. Small

scratches in the axial direction of the piston rod or polishing of the rod surface is
considered normal operating wear.

Yearly Change actuator seals if necessary. Actuator assemblies can require more or less

frequent seal changes depending on usage. External oil leakage and/or decreased
performance are indicators of seal wear. Seal replacement is considered a service
procedure; contact you MTS Service Engineer for additional information.

298 HSM: Maintenance

The series 298 Hydraulic Service Manifold requires the filter be changed
periodically.

86

Maintenance

Component Identification

Series 322 Load Unit

Mixing different brands of hydraulic fluid can contaminate your system.

CAUTION

Contaminated hydraulic fluid can cause premature wear of the hydraulic
components in your system.

Do not mix different brands of hydraulic fluid. MTS Systems Corporation
recommends using Mobil DTE-25 or Shell Tellus 46 AW hydraulic fluid.

The filter element should be replaced whenever:

• The indicator on the top of the filter housing is in the bypass position, which

indicates a dirty filter condition.

• The hydraulic fluid in the hydraulic power unit is changed.

Replace the filter element with one of the same rating or better.

F

ILTER PART NUMBER KIT NUMBER

3 micron (Beta3 = 75) 011-395-937 044-205-301

10 micron (Beta

= 75) 011-395-936 044-205-201

7.4

To change the filter element:

1. Ensure that system hydraulic pressure has been reduced to zero before
proceeding. To do this, turn off the hydraulic power unit and exercise the
actuator until it stops moving.

2. Turn off electrical power at the controller.

3. Place a waste fluid pan beneath the filter housing, which will accumulate
any small amount of drainage from the filter housing.

4. Remove the inlet filter bowl.

5. Remove the disposable filter element from the filter bowl.

6. Empty the oil in the filter bowl into the pan. Wipe out any remaining
sediment with a clean lint-free cloth.

7. Inspect the O-ring in the filter housing for any sign of deterioration. If
necessary, replace the defective O-ring (part number 010-010-726).

8. Lubricate the filter element and filter housing O-rings with clean hydraulic
fluid. Insert the replacement filter element into the filter bowl. Tighten the
filter bowl to 34–41 N·m (25–30 lbf·ft).

9. Apply low, then high, hydraulic pressure to the actuator manifold and
inspect the seal between the filter bowl and housing for any signs of
leakage. If leakage exists, turn off system hydraulic and electrical power and
repeat Steps 4 through 9.

Series 322 Load Unit Maintenance

87

252 Servovalve: Maintenance Overview

Maintaining the Series 252 Servovalves typically involves changing the filter
element (Series 252.3x only) and setting the mechanical null adjustment. Except
for these procedures, further disassembly, inspection, or repair of the servovalve
is not recommended and may void the servovalve warranty.

MTS does not recommend changing the 35-micron filter element in the Series

252.2x/.4x Servovalve (revision C). MTS hydraulic power supplies filter the
system hydraulic fluid at 3-microns absolute. The system filters will trap most
solid particle contaminants. If servovalve performance has deteriorated and the
cause has been isolated to the servovalve filter, return the servovalve to MTS for
service.

252 Servovalve: Replace the Filter Element

Under normal operating conditions, the 20-micron stainless steel filter used in the
servovalve should be replaced only if servovalve performance has deteriorated.
Ensure that other possible causes of poor performance, such as plugged system
filters and/or hydraulic power supply wear, have been eliminated before
replacing the servovalve filter.

Prerequisites You must have a filter kit that contains the necessary filter element replacement

parts. The filter for the Series 252.3x Servovalves is MTS part number 032-844-

101. Contact MTS Systems Corporation for the filter for the revision G Series

252.2x/4x Servovalves

88

Maintenance

Series 322 Load Unit

Procedure To replace the filter element, perform the following procedure. Care should be

1

4

3

2

Socket Head
Screws (4)

Filter Cover
Plate

Filter Plug

Filter Plug
O-Rings

Filter O-Ring

Filter

Filter Housing

Filter Cover

Model 252.2x/.4x Filter Location

(Revision G only)

Model 252.3x Filter Assembly

exercised to prevent dirt or other contaminants from entering the servovalve
body, filter passages, or manifold/actuator ports. Refer to the following figure
during the procedure.

10. Ensure that system hydraulic pressure has been reduced to zero before
proceeding. To do this, turn off the hydraulic power unit and exercise the
actuator until it stops moving. Turn off electrical power to the controller.

For the Series 252.2x/4x Servovalve proceed as follows:

Note This procedure only applies to revision G of the servovalve.

A. Remove the four socket head screws and washers that secure the filter

cover plug.

B. Thread one of the socket head screws, removed in Step A, into the filter

cover plug and pull it out of the filter housing.

C. Remove the filter disk.

Series 322 Load Unit Maintenance

89

D. Lightly lubricate the filter with clean hydraulic fluid and insert the

filter into the housing.

E. Secure the filter cover plate to the housing using the four socket head

screws and washers removed in Step A.

For the Series 252.3x Servovalve proceed as follows:

A. Remove the four socket head screws and washers that secure the filter

cover plate to the filter housing as shown below.

B. Remove the filter plug by threading one of the socket head screws,

removed in Step A, into the filter plug and pulling it out of the filter
housing. Remove the filter cover plate.

C. Remove the filter plug O-rings from the filter plug.

D. Remove the filter O-ring from the filter.

E. Remove the filter.

F. Lightly lubricate the filter O-ring with clean hydraulic fluid, install it

on the replacement filter, and insert the filter into the housing.

G. Lightly lubricate the filter plug O-rings with clean hydraulic fluid,

install them on the filter plug and install the filter plug.

H. Secure the filter cover plate to the housing using the four socket head

screws and washers removed in Step A. Tighten each socket head
screw until it is firmly seated against the filter cover plate. Using the
sequence shown in the previous figure, tighten the socket head screws
to 4.5 N·m (40 lb·in). Continue using the sequence and tighten the
socket head screws to a final torque of 9.60 N·m (85 lb·in).

11. Turn on electrical and hydraulic system power.

12. Apply low hydraulic pressure to the servovalve so that hydraulic fluid
gradually fills the filter cavity.

13. Apply high hydraulic pressure and check for leaks.

252 Servovalve: Adjust the Mechanical Null

This procedure describes how to adjust the mechanical null for the Series 252
Servovalve. The mechanical null adjustment aligns the servovalve spool to a
position that allows little or no actuator movement when there is no control
signal.

Prerequisites MTS Systems Corporation recommends that you read this procedure before

attempting to adjust the mechanical null. The mechanical null adjustment is quite
sensitive, and you should be familiar with the hazards that can be encountered
when performing the procedure.

Perform the servovalve mechanical null adjustment after the valve balancing
procedure (electrical compensation) has been completed and the results are
judged unsatisfactory.

90

Maintenance

Series 322 Load Unit

During the servovalve mechanical null adjustment procedure, the actuator must

WARNING

be able to move through full displacement in either direction without contacting a
reaction surface.

Valve balance

adjustments

MTS controllers have an electronic mechanical null adjustment called valve
balance. The valve balance adjustment is a convenient way to compensate for a
servovalve that needs a mechanical null adjustment. The adjustment introduces
an electrical offset signal that causes the servovalve to hold the position of the
actuator when a zero command is issued.

Sudden and unexpected actuator rod movement can cause serious injury to
personnel and/or damage to equipment.

Do not perform the following procedure without clearing the path of motion
of the actuator.

Ensure that all personnel, specimen/structures, and tools are away from the path
of motion of the actuator (crush zone).

1. Exercise the actuator.

The actuator should be exercised to warm it up. Electrical and mechanical
adjustments are more repeatable after the actuator is warmed up.

A. Select displacement control for the controller.

B. Disable the reset integrator or adjust the Reset control for zero.

C. Adjust the actuator for mid-displacement.

D. Turn on electrical and hydraulic system power.

E. Define a 50%, 0.1 Hz sine wave command and allow the actuator to

warm up for approximately one-half hour.

F. After the warmup period, stop the test program.

2. Check for actuator movement.

This task is a test to determine how to proceed.

Disconnect the servovalve cable and observe the actuator rod.

• If the actuator rod has no noticeable movement, the servovalve is at the

null position and does not need to be adjusted. Proceed to Step 4.

• If the actuator rod noticeably moves, the servovalve requires

adjustment. Proceed to Step 3.

3. Set the adjuster pin.

This task describes the mechanical null adjustment procedure.

A. Insert a 3/32-inch hex key into the adjustor pin socket. See the

following figure for the location of the adjustor pin.

Series 322 Load Unit Maintenance

91

Excessive torquing may shear off the adjustor pin eccentric.

CAUTION

Do not apply more than 12 lbf-in. (1.36 N•m) of torquing force to the adjustor
pin.

If the pin does not turn using very little force, proceed to Step C of this task.

B. Slowly rotate the adjustor pin until the actuator movement is reduced to

a minimum, and then go back to Step 2. If the pin does not turn using
very little force, proceed to the next step.

C. Reduce system pressure to low pressure (refer to the appropriate

controlling device product manual). Slowly rotate the adjustor pin until
the actuator movement is reduced to a minimum, and then proceed to
Step 4. If the adjustor pin still does not turn, proceed to the next step.

D. Ensure that system hydraulic pressure has been reduced to zero before

proceeding. To do this, turn off the hydraulic power unit and exercise
the actuator until it stops moving. Turn off electrical power to the
controller.

E. Remove the hex key and insert a 3/8-inch offset wrench over the self-

locking nut.

F. Insert a torque wrench with a 3/32-inch hex key head adapter into the

adjustor pin socket.

92

Maintenance

Series 322 Load Unit

G. Using the offset wrench, loosen (but do not remove) the self-locking

nut.

Mechanical Null Adjustor Pin

H. Turn the adjustor pin until the scribe mark on the adjustor pin is

pointing toward the base of the servovalve.

I. Tighten the self-locking nut until 1.13 to 1.36 N·m (10 to 12 lb-in) of

torque is needed to turn the adjustor pin, ensuring that the scribe mark
remains pointing toward the base of the servovalve.

J. Remove the torque wrench and offset wrench.

4. Finish the procedure.

A. Ensure that the actuator is warmed up. If not, go to Step 1.

B. Remove hydraulic and electric power from the system.

C. Reconnect the servovalve cable.

D. Reapply hydraulic and electric power to the system.

E. See your controller manual to complete the valve balance procedure.

Series 322 Load Unit Maintenance

93

94

Maintenance

Series 322 Load Unit

m

MTS Systems Corporation

14000 Technology Drive
Eden Prairie, Minnesota 55344-2290 USA
Toll Free Phone: [phone]

(within the U.S. or Canada)

Phone: [phone]

(outside the U.S. or Canada)
Fax: [phone]
E-mail: [e-mail]
Internet: www.mts.com

ISO 9001 Certified QMS