Management of Change Guide: Replacement of Fisher 685 Actuators with Fisher 785C Double-Acting Springless Actuators
Fisher Management of Change Guide: Replacement of Fisher 685 Actuators with Fisher 785C Double-Acting Springless Actuators Manuals & Guides
Management of Change Guide
May 2019
D352798X012
Replacement of Fisher™ 685 Actuators with
Fisher™ 785C Double-Acting Springless Actuators
Table of Contents
Management of Change ..................................2
Background ....................................................2
Question & Answer Checklist ..........................2
Comparison of Fisher 785C and 685 Actuators 5
Basic Design and Features ................................................... 5
Weight ............................................................................... 7
Envelope Dimensions ......................................................... 7
Conclusion ......................................................9
Management of Change
Management of Change (MOC) is a procedure used to proactively manage changes
that have the potential to impact safety or the process within a plant. Evaluating
new techniques for improving MOC approval procedures can have an impact on
plant efciency. Historically, upgrading obsolete products or replacing existing
process control equipment had been delayed or abandoned due to the extensive
paperwork involved in completing a complex MOC approval sheet.
Background
The Fisher 785C Series is a double-acting springless or single-acting or doubleacting spring-return actuator that provides accurate, high thrust output for up
to 610 mm (24 inch) travel sliding-stem valve applications. The purpose of this
document is to simplify the transition from existing double-acting springless piston
actuator technologies to the Fisher 785C double-acting springless actuator.
Contained in this guide are two sections, the rst contains questions and answers
and the second compares the Fisher 785C actuator to the Fisher 685 actuator.
The rst section helps users complete MOC approval documents when replacing
existing actuators with the 785C model. The second section helps users better
understand the differences and similarities between the 785C and the 685 actuator.
MOC: Fisher 685 to 785C Actuators
May 2019
D352798X012
Question & Answer Checklist
Q: Does the proposed modication cause any changes to the piping and
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instrumentation diagram (P&ID)?
A: No.
Q: Does the proposed modication change process chemistry,
technology, or operating and control philosophies?
A: No.
Q: Does the proposed modication change how the existing plant is
operated?
A: No.
Q: Does the proposed modication change process ows?
A: No.
Figure 1. Fisher 785C double-acting
springless actuator
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Q: Does the proposed modication change existing pressure relief cases?
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A: No.
Q: Does the proposed modication change the process description?
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A: No.
Q: Have the codes and standards to which the new equipment was
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designed changed?
A: No.
Q: Does the proposed modication change the materials of construction,
such as a change in material form (cast, forged, or alloy)?
A: No. The plant can specify the materials of constructions as desired.
MOC: Fisher 685 to 785C Actuators
May 2019
D352798X012
Q: Does the proposed modication introduce new equipment items that
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require periodic predictive maintenance?
A: No. The new equipment items will require the same periodic
predictive maintenance required by the old equipment items.
Q: Does the proposed modication change existing operator training
requirements?
A: No. Please refer to the instruction manual when performing
maintenance on the Fisher 785C actuator.
Q: Does the proposed modication introduce new equipment items
that require spare parts, training manuals, maintenance procedures
or training to teach the maintenance department how to maintain
them?
A: Yes, however the new equipment items have the same theory of
operation and maintenance procedures as the old equipment items.
Documentation for training and maintenance can be obtained in the
instruction manual or by contacting your local Emerson sales ofce.
Q: Does the proposed modication introduce new equipment items that
require spares or obsolete spares for existing equipment?
A: Yes. Spares for old equipment items cannot be used with new
equipment items due to differences in dimensions. Documentation
on recommended spares can be obtained by providing the two serial
numbers, located on the actuator, to your local Emerson sales ofce.
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Q: Does the proposed modication permanently remove the spares for
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existing pieces of equipment?
A: No.
Q: Does the proposed modication change the inspection scope or
inspection interval?
A: No.
Q: Does the proposed modication require welding work to be
performed?
A: No.
Q: Have the materials of construction been reviewed to ensure that the
metallurgy is correct?
A: No.
MOC: Fisher 685 to 785C Actuators
May 2019
D352798X012
4
Comparison of Fisher 785C and Fisher 685
Actuators
Even though the Fisher 785C and 685 actuators have identical theories of operation,
there are certain key differences and advantages in the design and feature set of
the 785C actuator. This section provides insight on the differences and similarities
between these two actuators.
Basic Design and Features
The 785C actuator has the same theory of operation, valve-to-actuator mounting
type, and valve stem connection diameters as the 685 actuator. The 785C actuator
can also be mounted and installed onto the same valves that the 685 actuator
is available for and currently installed on. Tables 1, 2, 3 and 4 provide side-byside comparisons of design specications, instrument compatibility, materials of
construction, and certications between the 785C and 685 actuators.
MOC: Fisher 685 to 785C Actuators
May 2019
D352798X012
Specication
Fisher 785C Actuator
(1)
Fisher 685 Actuator
(1)
Actuator Type Double-Acting Piston for Sliding Stem (Globe) Valves
Yoke Boss Diameter 5, 5H, or 7 inch 5H or 7 inch
Valve Stem
Connection
Manual Override
Capability
Top Mounted Handwheel (280 - 385)
1, 1 1/4, or 2 inch 1 1/4 or 2 inch
Manual Handpump (435 - 685)
Side Mounted Handwheel
Cylinder Diameter 280 to 685 mm (11 to 27 inches) 304 to 660 mm (12 to 26 inches)
Travel 25 to 609.6 mm (1 to 24 inches) 25 to 610 mm (1 to 24 inches)
Operating Pressure 2.7 to 12 bar (40 to 174 psig) 2.7 to 10.3 bar (40 to 150 psig)
Operating
Temperature Limits
(2)
Thrust
Standard: -20 to 100°C (-4 to 212°F)
Low Temp: -60 to 100°C (-76 to 212°F)
High Temp: -20 to 200°C (-4 to 392°F)
1600 KN (359,000 lbs.) 354 KN (79,639 lbs.)
Standard: -40 to 93°C (-40 to 200°F)
Low Temp: -54 to 93°C (-65 to 200°F)
High Temp: -29 to 204°C (-20 to 400°F)
Pressure Connections 3/4, 1/2, 1, or 1 1/4 NPT 3/4, 1, or 1 1/4 NPT
1. Representative of standard constructions
2. Thrust varies depending on supply pressure, cylinder diameter, and stroke direction (push or pull). Values listed are for the push stroke
direction.
Table 1. Design specications comparison
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MOC: Fisher 685 to 785C Actuators
May 2019
D352798X012
Instrument
Fisher 785C Actuator Fisher 685 Actuator
Compatible (Yes/No)
Fisher FIELDVUE™ DVC6000 Series Positioners No Yes
Fisher FIELDVUE DVC6200 Series Positioners Yes Yes
Fisher 2625 Volume Booster Yes Yes
Fisher SS-263 Volume Booster No (Available by Request) Yes
Fisher 377 Trip Valve Yes Yes
TopWorx™ GO Switch™ Position Sensor Yes Yes
Table 2. Instrument compatibility comparison
Part Fisher 785C Actuator Fisher 685 Actuator
Yoke Carbon Steel Carbon Steel
Piston Carbon Steel Carbon Steel
Cylinder Carbon Steel Carbon Steel
Upper/Lower Heads Carbon Steel Carbon Steel
Tie Bolt Carbon Steel or Stainless Steel Carbon Steel
Piston Rod Stainless Steel Stainless Steel
Stem Connector Carbon Steel or Stainless Steel Carbon Steel
Nameplate and
Travel Scale
Table 3. Materials of construction comparison for standard temperature range
Stainless Steel —
Certication Fisher 785C Actuator Fisher 685 Actuator
PED PED 2014/68/EU PED (97/23/EC)
ATEX ATEX Group II Category 2 Gas and Dust ATEX Group II Category 2 Gas and Dust
SIL
CUTR
Table 4: Certications comparison
Customs Union Technical Regulations
(CUTR) 010/2011 and 012/2011
Safety Instrumented System,
SIL 3 Capable
Customs Union Technical Regulations (CUTR)
Safety Instrumented System,
SIL 2 Capable
010/2011 and 012/2011
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Weight
See Table 5 for side-by-side comparisons of design weight without manual override
between the Fisher 785C and 685 actuators. For complete weight comparisons
check the Fisher 785C product bulletin and Fisher 685 product bulletin.
Fisher 785C Actuator Fisher 685 Actuator
Cylinder Size, mm (inch) Weight
280 (11) 142 (313)
335 (13) 173 (381)
385 (15) 240 (529)
435 (17) 283 (624)
485 (19) 325 (717) 508 (20) 430 (947)
535 (21) 373 (822) 558 (22) 505 (1114)
585 (23) 490 (1080) 609 (24) 702 (1548)
635 (25) 561 (1237) 660 (26) 804 (1771)
685 (27) 660 (1455) — —
1. Representative of actuator without handwheel.
2. Representative of actuator with 5H yoke boss.
(1,2)
, kg (lbs.) Cylinder Size, mm (inch) Weight
Cylinder sizes not available for maximum travel of
203 mm (8 inch)
MOC: Fisher 685 to 785C Actuators
May 2019
D352798X012
(1,2)
, kg (lbs.)
Table 5: Weight comparison
Envelope Dimensions
Refer to Tables 6, 7, and 8 with Figure 2 for a comparison of envelope dimensions
between the 785C and 685 actuators.
Width, mm (Inches)
785C Size 485 (19) 685 Size 508 (20) 785C Size 535 (21) 685 Size 558 (22)
Without Manual
Override
Table 6: Width envelope dimensions
Travel, mm
(inch)
785C Size 485 (19.09) 685 Size 508 (20) 785C Size 535 (21.06) 685 Size 558 (22)
102 (4) 767 (30.20) 754 (29.69) 798 (31.42) 754 (29.69)
203 (8) 952 (37.48) 941 (37.06) 994 (39.13) 941 (37.06)
Table 7: Height envelope dimensions for actuators with 5H yoke boss diameter
630 (25) 591 (23) 680 (27) 654 (26)
Height for a 127 mm (5H) Yoke Boss Diameter, mm (inches)
Without Manual Override
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MOC: Fisher 685 to 785C Actuators
May 2019
D352798X012
Travel, mm
(inch)
Without Manual Override
785C Size 485 (19.09) 685 Size 508 (20) 785C Size 535 (21.06) 685 Size 558 (22)
102 (4) 797 (31.38) 786 (30.94) 799 (31.46) 786 (30.94)
203 (8) 1028 (79.84) 1018 (40.06) 1030 (40.55) 1018 (40.06)
Table 8: Height envelope dimensions for actuators with 7 yoke boss diameter
Height for a 178 mm (7 inch) Yoke Boss Diameter, mm (inches)
Figure 2: Fisher 785C Double-Acting Springless
Without Manual Override Actuator
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Conclusion
Introducing the Fisher 785C actuator in addition to the Fisher 685 actuator will not
affect Fisher 685 actuators currently installed in plants. The Fisher 785C actuator
offers new sizes and features in addition to the previous 685 actuator offerings and
will offer at least the same application coverage range as the 685 actuators.
Please contact your local Emerson sales ofce for additional details or questions
regarding Fisher 785C actuators.
MOC: Fisher 685 to 785 Actuators
May 2019
D352798X012
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