Danfoss S90 Service guide
Service Manual
Series 90 Pumps
www.danfoss.com
Service Manual
Series 90 Pumps
Revision history Table of revisions
Date Changed Rev
February 2020 Added HCEDC information and changed document number from 520L0818 0203
August 2015 edits to Aux Pad minor repair 0102
December 2014 Danfoss layout BA
June 2012 minor edits AD
December 2011 minor edits AC
April 2008 page 70 correction to bolt torques AB
October 2007 First printing AA
2 | © Danfoss | February 2020 AX152886483063en-000203
Service Manual
Series 90 Pumps
Contents
Introduction
Operation
Operating parameters
Technical specifications
Initial start-up procedure
Pressure measurement
Overview..............................................................................................................................................................................................5
Warranty.............................................................................................................................................................................................. 5
General instructions........................................................................................................................................................................ 5
Remove the unit.......................................................................................................................................................................... 5
Replace all O-rings and gaskets............................................................................................................................................. 5
Safety Precautions............................................................................................................................................................................6
Unintended Machine Movement..........................................................................................................................................6
Flammable Cleaning Solvents................................................................................................................................................6
Fluid Under Pressure..................................................................................................................................................................6
Personal Safety.............................................................................................................................................................................6
Symbols used in Danfoss literature............................................................................................................................................7
Design...................................................................................................................................................................................................7
The system circuit.............................................................................................................................................................................8
The basic closed circuit............................................................................................................................................................. 8
Case drain and heat exchanger..............................................................................................................................................9
S90 charge pump operation......................................................................................................................................................11
S90 charge relief valve operation.............................................................................................................................................11
S90 multi-function valve operation.........................................................................................................................................11
S90 pressure limiter/high pressure relief valve operation..............................................................................................12
S90 system check valve operation...........................................................................................................................................12
S90 bypass valves operation......................................................................................................................................................12
S90 speed sensor operation.......................................................................................................................................................13
S90 filtration options.................................................................................................................................................................... 13
S90 pressure override (POR) operation..................................................................................................................................13
S90 MDC operation....................................................................................................................................................................... 14
S90 non-linear MDC operation................................................................................................................................................. 14
S90 MDC solenoid override valve operation........................................................................................................................14
Neutral start switch (NSS) for MDC..........................................................................................................................................14
S90 HDC operation........................................................................................................................................................................14
S90 EDC operation.........................................................................................................................................................................15
S90 Automotive control (FBA II B) operation.......................................................................................................................15
S90 3-Position (FNR) electric control operation..................................................................................................................15
High Current Electrical Displacement Control (HCEDC).................................................................................................. 15
HCEDC Principle........................................................................................................................................................................15
HCEDC Operation..................................................................................................................................................................... 16
Manual OverRide (MOR).............................................................................................................................................................. 16
S90 Input speed..............................................................................................................................................................................18
S90 system pressure......................................................................................................................................................................18
S90 charge pressure......................................................................................................................................................................18
S90 charge inlet pressure............................................................................................................................................................19
Case pressure...................................................................................................................................................................................19
Temperature and viscosity......................................................................................................................................................... 19
Fluid and filter recommendations........................................................................................................................................... 19
Overview........................................................................................................................................................................................... 21
Features and options....................................................................................................................................................................21
Operating parameters..................................................................................................................................................................21
Fluid specifications........................................................................................................................................................................21
General ..............................................................................................................................................................................................23
Start-up procedure........................................................................................................................................................................23
Required tools.................................................................................................................................................................................24
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Service Manual
Series 90 Pumps
Contents
Troubleshooting
Adjustments
Minor repair
Torque chart
Port locations and gauge installation.....................................................................................................................................24
Overview........................................................................................................................................................................................... 27
Neutral difficult or impossible to find.....................................................................................................................................27
System operating hot...................................................................................................................................................................27
Transmission operates normally in one direction only....................................................................................................27
System will not operate in either direction.......................................................................................................................... 28
Low motor output torque...........................................................................................................................................................28
Improper motor output speed..................................................................................................................................................28
System noise or vibration........................................................................................................................................................... 29
System response is sluggish...................................................................................................................................................... 29
Standard procedures, inspections, and adjustments....................................................................................................... 30
Adjustments.....................................................................................................................................................................................30
Charge pressure relief valve adjustment...............................................................................................................................30
Multi-function valve pressure adjustment............................................................................................................................32
Engaging the bypass function.................................................................................................................................................. 33
Pressure override (POR) valve pressure adjustment (option for 180 frame size)....................................................34
Displacement limiter adjustment............................................................................................................................................ 35
Control Neutral Adjustment.......................................................................................................................................................36
Verify neutral setting...............................................................................................................................................................37
Servo Adjustment Side M4....................................................................................................................................................37
Standard manual displacement control (MDC) adjustment.......................................................................................... 38
Non-linear manual displacement control (MDC)............................................................................................................... 38
MDC Neutral start switch (NSS) adjustments.......................................................................................................................39
Checking switch continuity........................................................................................................................................................42
Hydraulic displacement control (HDC) and electric displacement control (EDC) adjustment..........................43
Speed sensor adjustment........................................................................................................................................................... 44
Standard procedures....................................................................................................................................................................46
Shaft seal and shaft replacement.............................................................................................................................................46
Multi-function valve cartridges.................................................................................................................................................49
Multi-function valve cartridges - pre 1988............................................................................................................................51
Pressure override valve (option for 180 frame size).......................................................................................................... 53
Charge pressure relief valve.......................................................................................................................................................53
Adding an Auxiliary pad to a pump previously without one.........................................................................................55
Auxiliary pad....................................................................................................................................................................................56
Charge pump...................................................................................................................................................................................57
Integral charge pressure filter replacement.........................................................................................................................61
Pump control cover plate........................................................................................................................................................... 63
Displacement control orifices....................................................................................................................................................63
Displacement control orifice check valve............................................................................................................................. 64
Displacement control adapter plate (early production 130 pumps only).................................................................64
Manual displacement control (MDC)......................................................................................................................................65
Solenoid override valve for MDC..............................................................................................................................................66
Solenoid override valve for MDC with pressure released brake...................................................................................67
Hydraulic and electric displacement controls.....................................................................................................................68
Pressure control pilot (PCP) for electric displacement control (EDC)..........................................................................70
3-Position (FNR) electric control...............................................................................................................................................70
Displacement control filter screens.........................................................................................................................................72
Speed sensor................................................................................................................................................................................... 72
Control Module Repair.................................................................................................................................................................73
Replace control solenoids/actuator housing.......................................................................................................................75
Fastener size and torque chart..................................................................................................................................................76
Plug size and torque chart..........................................................................................................................................................77
Fasteners and plugs...................................................................................................................................................................... 78
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Service Manual
Series 90 Pumps
Introduction
Overview
Warranty
This manual includes information for the installation, maintenance, and minor repair of Series 90 axial
piston closed circuit pumps. It includes a description of the unit and its individual components,
troubleshooting information, and minor repair procedures.
Performing minor repairs requires you remove the unit from the vehicle/machine. Thoroughly clean the
unit before beginning maintenance or repair activities. Since dirt and contamination are the greatest
enemies of any type of hydraulic equipment, follow cleanliness requirements strictly. This is especially
important when changing the system filter and when removing hoses or plumbing.
A worldwide network of Danfoss Global Service Partners (GSPs) is available for major repairs. Danfoss
trains GSPs and certifies their facilities on a regular basis. You can locate your nearest ASC using the
distributor locator at www.DanfossPower Solutions.com. Click on the Sales and Service link.
Performing installation, maintenance, and minor repairs according to the procedures in this manual will
not affect your warranty. Major repairs requiring the removal of a unit’s rear or side cover voids the
warranty unless done by a Danfoss Authorized Service Center.
General instructions
Follow these general procedures when repairing this product.
Remove the unit
If necessary, remove the unit from the vehicle/machine. Chock the wheels on the vehicle or lock the
mechanism to inhibit movement. Be aware that hydraulic fluid may be under high pressure and/or hot.
Inspect the outside of the pump and fittings for damage. Cap hoses after removal to prevent
contamination.
Keep it clean
Cleanliness is a primary means of assuring satisfactory pump life, on either new or repaired units. Clean
the outside of the pump thoroughly before disassembly. Take care to avoid contamination of the system
ports. Cleaning parts by using a clean solvent wash and air drying is usually adequate.
As with any precision equipment, keep all parts free of foreign materials and chemicals. Protect all
exposed sealing surfaces and open cavities from damage and foreign material. If left unattended, cover
the pump with a protective layer of plastic.
Replace all O-rings and gaskets
Danfoss recommends that you replace all O-rings, seals and gaskets. Lightly lubricate all O-rings with
clean petroleum jelly prior to assembly.
Secure the unit
For repair, place the unit in a stable position with the shaft pointing downward. It will be necessary to
secure the pump while removing and torquing end covers, controls, and valves.
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Service Manual
Series 90 Pumps
Introduction
Safety Precautions
Always consider safety precautions before beginning a service procedure. Protect yourself and others
from injury. Take the following general precautions whenever servicing a hydraulic system.
Unintended Machine Movement
Unintended movement of the machine or mechanism may cause injury to the technician or bystanders.
Secure the machine or disable/disconnect the mechanism while servicing to protect against unintended
movement.
Flammable Cleaning Solvents
Some cleaning solvents are flammable.
Do not use cleaning solvents in an area where a source of ignition may be present to avoid possible fire.
Fluid Under Pressure
Escaping hydraulic fluid under pressure can have sufficient force to penetrate your skin causing serious
injury and/or infection. This fluid may also be hot enough to cause burns.
Relieve pressure in the system before removing hoses, fittings, gauges, or components. Never use your
hand or any other body part to check for leaks in a pressurized line. Use caution when dealing with
hydraulic fluid under pressure. Seek medical attention immediately if you are cut by hydraulic fluid.
Personal Safety
Protect yourself from injury whenever servicing a hydraulic system.
Use proper safety equipment, including safety glasses, at all times.
Hazardous Material
Hydraulic fluid contains hazardous material.
Avoid prolonged contact with hydraulic fluid. Always dispose of used hydraulic fluid according to state,
and federal environmental regulations.
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Service Manual
Series 90 Pumps
Introduction
Symbols used in Danfoss literature
WARNING may result in injury Tip, helpful suggestion
CAUTION may result in damage to product or
property
Reusable part Apply grease / petroleum jelly
Non-reusable part, use a new part Apply locking compound
Non-removable item Inspect for wear or damage
Option - either part may exist Clean area or part
Superseded - parts are not interchangeable Be careful not to scratch or damage
Measurement required Note correct orientation
Flatness specification Mark orientation for reinstallation
Parallelism specification Torque specification
External hex head Press in - press fit
Internal hex head Pull out with tool – press fit
Torx head Cover splines with installation sleeve
O-ring boss port Pressure measurement/gauge location or
Lubricate with hydraulic fluid
specification
Design
The symbols above appear in the illustrations and text of this manual. They are intended to communicate
helpful information at the point where it is most useful to the reader. In most instances, the appearance
of the symbol itself denotes its meaning. The legend above defines each symbol and explains its purpose.
Danfoss Series 90 closed circuit piston pumps convert input torque into hydraulic power. The input shaft
transmits rotational force to the cylinder block. Bearings support the input shaft at the front and rear of
the pump. The shaft is splined into the cylinder block. A lip-seal at the front end of the pump prevents
leakage where the shaft exits the pump housing. The spinning cylinder block contains nine reciprocating
pistons. A ball joint at one end connects each piston to a brass slipper. Fixed-clearance hold-down
brackets keep the slippers in contact with the swashplate. The reciprocating movement of the pistons
occurs as the slippers slide against the inclined swashplate during rotation. The valve plate connects one
half of the cylinder block to low pressure and the other half to high pressure. As each piston cycles in and
out of its bore, fluid is drawn from the inlet and displaced to the outlet thereby imparting hydraulic
power into the system. A small amount of fluid flows from the cylinder block/valve plate and slipper/
swashplate interfaces for lubrication and cooling. Case drain ports return this fluid to the reservoir.
The angle of the swashplate controls the volume of fluid displaced into the system. The servo piston
forces the swashplate into an inclined position. The pump control, acting on input from the operator, by
modulating pressure balance across the servo piston, sets displacement in the system circuit.
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P106 648E
Slider block
Servo piston
Servo arm
Displacement control
Cradle bearing
Charge pump
Swashplate
Cradle guide
Feedback linkage
Roller bearing
Shaft
Piston
Slipper
Valve plate
Cylinder block
Input shaft
Rear
bushing
Bushing
seal
Service Manual
Series 90 Pumps
Introduction
Cross section
The system circuit
The basic closed circuit
Hydraulic lines connect the main ports of the pump to the main ports of the motor. Fluid flows in either
direction from the pump to the motor then back to the pump in this closed circuit. Either of the hydraulic
lines can be under high pressure. In pumping mode the position of the pump swashplate determines
which line is high pressure as well as the direction of fluid flow.
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Input
PV
MF
Case drain line
Output
Flow (Bi-directional)
Reservoir
P104 120E
Pump Motor
Working loop (low pressure)
Control fluid
Suction line
Case drain fluid
Working loop (high pressure)
Motor swashplate
Loop flushing valve
Displacement control valve
Heat exchanger bypass valve
Reservoir
Vacuum gauge
Purge relief valve
Fixed displacement motor
Output shaft
Multi-function valve
Charge pump
To
pump
case
Servo
pressure
relief valves
Servo control cylinder
Pump swashplate
Input shaft
Reversible variable
displacement pump
Servo control cylinder
Heat exchanger
Multi-function valve
Charge pressure relief valve
Orificed check
valve
Control handle
P102 000
Service Manual
Series 90 Pumps
Introduction
System circuit diagram
Basic closed circuit diagram
Case drain and heat exchanger
The pump and motor require case drain lines to remove hot fluid from the system. The topmost port
drains the motor to ensure the case remains full of fluid. Fluid routes through the lower drain port on the
pump and out the topmost port to the reservoir. A heat exchanger, with a bypass valve, cools the case
drain fluid before it returns to the reservoir.
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P104 126E
M4
M5
L2
S
L1
X5
M1
M2
A
B
M3
Service Manual
Series 90 Pumps
Introduction
Pump schematic
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Case
drain
line
Charge relief valve
Charge
pump
System
check
valves
Input
Inlet filter
Tank
PV PF
P104 121E
Charge pressure
P106 157E
Service Manual
Series 90 Pumps
Operation
S90 charge pump operation
The charge pump is necessary to supply cool fluid to the system, to maintain positive pressure in the
main system loop, to provide pressure to operate the control system, and to make up for internal leakage.
Charge pressure must be at its specified pressure under all conditions to prevent damage to the
transmission.
The charge pump is a fixed-displacement, gerotor type pump driven off the main pump shaft. The charge
relief valve limits charge pressure.
Pump charge system
S90 charge relief valve operation
S90 multi-function valve operation
The charge relief valve on the pump maintains charge pressure at a designated level. A direct-acting
poppet valve relieves fluid when charge pressure reaches a certain level. This level is nominally set
referencing case pressure at 1500 rpm. This nominal setting assumes the pump is in neutral (zero flow). In
forward or reverse, charge pressure is lower. The pump model code specifies the charge relief valve
setting.
Charge pressure relief valve
The multi-function valve incorporates the system check valve, the pressure limiter valve, the high
pressure relief valve, and the bypass valve in a replaceable cartridge. These functions are described
separately. There are two multi-function valve cartridges in each Series 90 pump to handle functions in
either direction. See corresponding sections for adjustments and repairs.
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High pressure
relief / check
valve poppet
Pressure limiter
valve poppet
Bypass
actuator
Pressure limiter
adjustment screw
Pressure limiter
lock nut
Pressure limiter housing
Check valve
poppet
Bypass
P104 122E
Servo Pres.
Relief Valve
Charge
pressure
relief valve
Multi-function valve
Multi-function valve
To control
Servo piston
Servo piston
Port "A"
Port "B"
Bypass
adjustment
P104 123E
Service Manual
Series 90 Pumps
Operation
Multi-function valve
Some multi-function valves do not include a pressure limiter valve
S90 pressure limiter/high pressure relief valve operation
Series 90 pumps have a sequenced pressure limiting system and high pressure relief valves. When the
system pressure reaches the preset, the pressure limiter system rapidly de-strokes the pump to limit
system pressure. For unusually rapid load application, the high pressure relief valve immediately limits
system pressure by cross-porting system flow. The pressure limiter valve acts as the pilot for the high
pressure relief valve spool. The high pressure relief valve is sequenced to operate at approximately 35 bar
(500 psi) above the level that initiates the pressure limiter valve.
Circuit diagram showing pressure control mechanism
For some applications, such as dual path vehicles, the pressure limiter function may be defeated so that
only the high pressure relief valve function remains.
S90 system check valve operation
The system check valves allow pressurized flow from the charge pump to enter the low pressure side of
the loop. This is needed as the pump generally loses system pressure due to lubrication/cooling flow and
other factors. Since the pump operates in either direction, the system uses two check valves to direct the
charge supply into the low pressure lines. The system check valves are part of the multi-function valve
assembly.
S90 bypass valves operation
You can operate the bypass valves to move the vehicle or mechanical function when the pump is not
12 | © Danfoss | February 2020 AX152886483063en-000203
running. Manually resetting the valve position opens the valve. The bypass valves are built into the multifunction valves.
Charge pump
Filter
Hydraulic fluid reservoir
Adjustable
charge pressure relief valve
To pump case
To low
loop and
control
Manometer
P102 003E
To pump case
Charge pump
Hydraulic fluid reservoir
Filter
To low
pressure
side and
control
Screen
Adjustable
charge pressure
relief valve
P102 004E
Service Manual
Series 90 Pumps
Operation
S90 speed sensor operation
S90 filtration options
An optional speed sensor can provide unit speed information. The sensor reads a magnetic ring on the
unit’s cylinder block. See the corresponding section to locate, install, and adjust the speed sensor.
Series 90 pumps may have either suction or charge pressure filtration to filter the fluid entering the
circuit.
The suction filter is in the circuit between the reservoir and the inlet to the charge pump, as shown
below. The use of a filter contamination monitor is recommended.
Suction filtration
S90 suction filtration operation
The suction filter is in the circuit between the reservoir and the inlet to the charge pump, as shown
above. The use of a filter contamination monitor is recommended.
S90 charge pressure filtration operation
Filtration options R, T, P, and L are pressure filters mounted on the pump or remotely for ease of servicing.
You will typically find a 100-125 µm mesh screen, in the reservoir or the charge inlet. This system requires
a filter capable of withstanding charge pressure (reference to atmosphere - add case pressure).
Charge pressure filtration
S90 pressure override (POR) operation
The pressure override valve is only available for the 180cc frame size only.
The Pressure OverRide valve (POR) modulates control pressure to maintain a pump displacement which
produces a system pressure level less than or equal to the POR setting. For unusually rapid load
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Danfoss | February 2020 AX152886483063en-000203 | 13
application, the high pressure relief valve function of the multi-function valves is available to also limit
the pressure level.
The pressure override consists of a three-way normally open valve which operates in series with the
pump displacement control. Control supply pressure normally ports through the POR valve to the
Shuttle
valve
Multi-function valve
Multi-function valve
Bypass
adjustment
Charge pressure
relief valve
Pressure
override control valve
To control
Port "A"
Port "B"
P104 124E
Service Manual
Series 90 Pumps
Operation
displacement control valve. If the system demands a pressure above the override setting, the POR valve
overrides the control by reducing the pressure to the displacement control. As the control pressure
reduces, the internal forces rotating the swashplate overcome the force of the servo pistons and
decreases the pump’s displacement.
POR-Valve (180 frame size only)
S90 MDC operation
The manual displacement control converts a mechanical input signal to a hydraulic signal using a spring
centered four-way servo valve. This valve ports hydraulic pressure to either side of a dual-acting servo
piston. The servo piston rotates the cradle swashplate through an angular rotation of ±17°, varying the
pump’s displacement from full in one direction to full in the opposite direction. The angular position of
the pump swashplate is proportional to the rotation of the control input shaft.
S90 non-linear MDC operation
The non-linear manual displacement control operates in the same manner except that it is designed so
the change in the angular position of the pump swashplate progressively increases as the control input
shaft is rotated toward its maximum displacement position.
S90 MDC solenoid override valve operation
A solenoid override valve option is available for the MDC. This safety feature returns the swashplate to
zero displacement. It is available in normally open (activate to allow) or normally closed (activate to
disallow) options.
Neutral start switch (NSS) for MDC
The neutral start switch is an optional feature available with the MDC. When connected properly with the
vehicle’s electrical system, the neutral start switch ensures that the prime mover can start only when the
control is in neutral position.
S90 HDC operation
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The hydraulic displacement control uses a hydraulic input signal to operate a spring-centered four-way
servo valve. This valve ports hydraulic pressure to either side of a dual-acting servo piston. The servo
piston rotates the cradle swashplate through an angular rotation of ±17°, thus varying the pump’s
displacement from full displacement in one direction to full displacement in the opposite direction. The
angular position of the pump swashplate is proportional to input pressure.
P003 191
Service Manual
Series 90 Pumps
Operation
S90 EDC operation
The electric displacement control uses a Pressure Control Pilot (PCP) valve to modulate pressure balance
across the spring-centered four-way servo valve. The PCP valve converts a DC electrical input signal to a
hydraulic signal. The servo valve ports hydraulic pressure to either side of a dual-acting servo piston. The
servo piston rotates the swashplate through an angular rotation of ±17°, varying the pump’s
displacement. The angular position of the swashplate is proportional to the EDC input.
S90 Automotive control (FBA II B) operation
The automotive control allows the operator to drive a vehicle similar to an automobile with an automatic
transmission. The automotive control includes a three-position electric control to provide direction
control.
S90 3-Position (FNR) electric control operation
This control utilizes a 12 or 24 Vdc electrically operated spool valve to port pressure to either side of the
pump servo piston. Energizing one of the solenoids causes the pump to go to its maximum displacement
in the corresponding direction. All functions of the three-position (FNR) electric control are preset at the
factory
High Current Electrical Displacement Control (HCEDC)
HCEDC Principle
An HCEDC is a displacement (flow) control. Pump swashplate position is proportional to the input
command and therefore vehicle or load speed (excluding influence of efficiency), is dependent only on
the prime mover speed or motor displacement.
The High Current Electrical Displacement Control (HCEDC) consists of a pair of proportional solenoids on
each side of a three-position, four-way porting spool. The proportional solenoid applies a force input to
the spool, which ports hydraulic pressure to either side of a double acting servo piston. Differential
pressure across the servo piston rotates the swashplate, changing the pump‘s displacement from full
displacement in one direction to full displacement in the opposite direction. Under some circumstances,
such as contamination, the control spool could stick and cause the pump to stay at some displacement.
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Feedback from
Swash plate
PTF00B
M14
1C2C
F00A
P003 478E
W
Service Manual
Series 90 Pumps
Operation
HCEDC schematic
A serviceable 125 μm screen is located in the supply line immediately before the control porting spool.
HCEDC Operation
S90 HCEDC’s are current driven controls requiring a Pulse Width Modulated (PWM) signal. Pulse width
modulation allows more precise control of current to the solenoids. The PWM signal causes the solenoid
pin to push against the porting spool, which pressurizes one end of the servo piston, while draining the
other. Pressure differential across the servo piston moves the swashplate.
A swashplate feedback link, opposing control links, and a linear spring provide swashplate position force
feedback to the solenoid. The control system reaches equilibrium when the position of the swashplate
spring feedback force exactly balances the input command solenoid force from the operator. As
hydraulic pressures in the operating loop change with load, the control assembly and servo/swashplate
system work constantly to maintain the commanded position of the swashplate.
The HCEDC incorporates a positive neutral deadband as a result of the control spool porting, pre-loads
from the servo piston assembly, and the linear control spring. Once the neutral threshold current is
reached, the swashplate is positioned directly proportional to the control current. To minimize the effect
of the control neutral deadband, we recommend the transmission controller or operator input device
incorporate a jump up current to offset a portion of the neutral deadband.
Manual OverRide (MOR)
The neutral position of the control spool does provide a positive pre-load pressure to each end of the
servo piston assembly.
When the control input signal is either lost or removed, or if there is a loss of charge pressure, the springloaded servo piston will automatically return the pump to the neutral position.
All high current controls are standard with Manual Over Ride (MOR), used for temporary actuation of the
control to aid in diagnostics.
Unintended MOR operation will cause the pump to go into stroke. The vehicle or device must always be
in a safe condition (i.e. vehicle lifted off the ground) when using the MOR function. The MOR plunger has
a 4 mm diameter and must be manually depressed to be engaged. Depressing the plunger mechanically
moves the control spool which allows the pump to go on stroke. The MOR should be engaged
anticipating a full stroke response from the pump.
Warning
An O-ring seal is used to seal the MOR plunger where initial actuation of the function will require a force
of 45 N to engage the plunger. Additional actuations typically require less force to engage the MOR
plunger. Proportional control of the pump using the MOR should not be expected.
Refer to the control flow table for the relationship of solenoid to direction of flow.
16 | © Danfoss | February 2020 AX152886483063en-000203
P003 204
C1C2
P108758
Service Manual
Series 90 Pumps
Operation
MOR Schematic diagram (EDC shown)
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Danfoss | February 2020 AX152886483063en-000203 | 17
W
Service Manual
Series 90 Pumps
Operating parameters
S90 Input speed
There are three acceptable input speeds that the S90 pump should operate in. The input speeds are
Minimum speed, Continuous speed and Maximum speed.
Minimum speed is the lowest input speed recommended during engine idle condition. Operating below
minimum speed limits the pump’s ability to maintain adequate flow for lubrication and power
transmission.
Continuous speed is the highest input speed recommended at full power condition. Operating at or below
this speed should yield satisfactory product life.
Maximum speed is the highest operating speed permitted. Exceeding maximum speed reduces product
life and can cause loss of hydrostatic power and braking capacity. Never exceed the maximum speed
limit under any operating conditions.
When determining speed limits for a particular application see Danfoss publication BLN-9884 Pressure
and speed limits.
Warning
Unintended vehicle or machine movement hazard
Exceeding maximum speed may cause a loss of hydrostatic drive line power and braking capacity. You
must provide a braking system, redundant to the hydrostatic transmission, sufficient to stop and hold the
vehicle or machine in the event of hydrostatic drive power loss.
S90 system pressure
S90 charge pressure
System pressure is the differential pressure between system ports A and B. It is the dominant operating
variable affecting hydraulic unit life. High system pressure, which results from high load, reduces
expected life.
Continuous pressure is the average, regularly occurring operating pressure. Operating at or below this
pressure should yield satisfactory product life.
Maximum pressure is the highest intermittent pressure allowed. Maximum machine load should never
exceed this pressure. For all applications, the load should move below this pressure.
All pressure limits are differential pressures referenced to low loop (charge) pressure. Subtract low loop
pressure from gauge readings to compute the differential.
System pressure must remain at or below continuous pressure during normal operation to achieve
expected life.
An internal charge relief valve regulates charge pressure. The charge pump supplies the control with
pressure to operate the swashplate and to maintain a minimum pressure in the low side of the
transmission loop.
Minimum charge pressure is the lowest pressure allowed to maintain a safe working condition in the low
side of the loop. Minimum control pressure requirements are a function of speed, pressure, and
swashplate angle, and may be higher than the minimum charge pressure shown in the operating
parameters table.
Maximum charge pressure is the highest charge pressure allowed by the charge relief adjustment, and
provides normal component life. You can use elevated charge pressure as a secondary means to reduce
the swashplate response time.
The charge pressure setting in the order code is the set pressure of the charge relief valve with the pump
in neutral, operating at 1800 min-1 (rpm), and with a fluid viscosity of 32 mm2/sec (150 SUS). The charge
pressure setting is referenced to case pressure. Charge pressure is the differential pressure above case
pressure.
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Operating parameters
S90 charge inlet pressure
Case pressure
Temperature and viscosity
At normal operating temperature charge inlet pressure must not fall below rated charge inlet pressure.
Minimum charge inlet pressure is only allowed at cold start conditions. In some applications it may be
necessary to warm up the fluid by running the engine at limited speed until the system fluid temperature
reaches an acceptable level.
Under normal operating conditions, do not exceed the rated case pressure. During cold start, maintain the
case pressure below maximum intermittent case pressure.
Caution
Possible component damage or leakage
Operation with case pressure in excess of stated limits may damage seals, gaskets, and/or housings,
causing external leakage. Performance may also be affected since charge and system pressure are
additive to case pressure.
Temperature
The high temperature limits apply at the hottest point in the transmission loop, which is normally the
motor case drain. Maintain system temperature below the quoted rated temperature.
Never exceed the maximum intermittent temperature.
Cold oil will generally not affect the durability of the transmission components, but it may affect the
ability of oil to flow and transmit power; therefore temperatures should remain 16 °C [30 °F] above the
pour point of the hydraulic fluid.
The minimum temperature relates to the physical properties of component materials.Size heat
exchangers to keep the fluid within these limits. Test heat exchangers to verify that these temperature
limits are not exceeded.
Viscosity
For maximum efficiency and bearing life, ensure the fluid viscosity remains in the recommended range.
Minimum viscosity should be encountered only during brief occasions of maximum ambient temperature
and severe duty cycle operation.
Maximum viscosity should be encountered only at cold start.
Fluid and filter recommendations
To ensure optimum pump life, perform regular maintenance of the fluid and filter. Contaminated fluid is
the main cause of unit failure. Maintain fluid cleanliness when servicing.
Check the reservoir daily for proper fluid level, the presence of water, and rancid fluid odor. Fluid
contaminated by water may appear cloudy or milky or free water may settle in the bottom of the
reservoir. Rancid odor indicates the fluid has been exposed to excessive heat. Change the fluid
immediately if these conditions occur. Correct the problem immediately.
Inspect vehicle for leaks daily.
Change the fluid and filter per the vehicle/machine manufacturer’s recommendations or at the intervals
shown in the table. Change fluid after first 500 hours.
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Operating parameters
Fluid and filter change interval
Reservoir type Max oil change interval
Sealed 2000 hours
Breather 500 hours
Caution
High temperatures and pressures result in accelerated fluid aging. Change fluid more frequently if
operating under extreme conditions.
Change the fluid more frequently if it becomes contaminated with foreign matter (dirt, water, grease,
etc.) or if the fluid is subjected to temperature levels greater than the recommended maximum.
Dispose of used hydraulic fluid properly. Never reuse hydraulic fluid.
Change filters whenever the fluid is changed or when the filter indicator indicates a filter change. Replace
all fluid lost during filter change.
For detailed filtration information, see Danfoss publication 520L0463 Fluids and Filtration. For
information on biodegradable fluids see Danfoss publication 520L0465 Biodegradable Hydraulic Fluids.
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Technical specifications
Overview
Specifications and operating parameters for pumps appear here for reference.
Features and options
Model Series 90 Pumps
Mount SAE B, SAE C and E (SAE J 744)
Pump type Axial piston type
Rotation Bidirectional
Installation position Discretionary: Housing must always be filled with hydraulic fluid. Do not install with control on bottom.
Input shafts Splined
Control options MDC (with options), EDC, HDC, FNR
Operating parameters
Parameter Unit Pressure
System pressure Rated bar
Maximum 480 [7000]
Minimum low loop 10 [150]
Charge pressure Minimum bar
Maximum 35 [508]
Charge inlet pressure Rated bar (absolute)
Minimum (cold start) 0.2 [24]
Case pressure Rated bar
Maximum 5.0 [75]
[psi]
[psi]
[in Hg vacuum]
[psi]
420 [6000]
10 [150]
0.7 [9]
3.0 [40]
Parameter Unit Frame size
042 055 075 100 130 180 250
Displacement
(maximum)
Minimum speed min-1 (rpm) 500 500 500 500 500 500 500
Rated speed min-1 (rpm) 4200 3900 3600 3300 3100 2600 2300
Maximum speed min-1 (rpm) 4600 4250 3950 3650 3400 2850 2500
Maximum attainable speed at
maximum displacement
Theoretical torque at maximum
displacement
Weight (base unit only) kg
cm³
[in³]
min-1 (rpm) 5000 4700 4300 4000 3700 3150 3750
N•m/bar
[lbf•in/1000
psi]
[lb]
42
[2.56]
0.67
[380]
34
[75]
55
[3.35]
0.88
[530]
40
[88]
75
[4.57]
1.19
[730]
49
[108]
100
[6.10]
1.59
[870]
68
[150]
130
[7.93]
2.07
[1260]
88
[195]
180
[10.98]
2.87
[1750]
136
[300]
250
[15.25]
3.97
[2433]
154
[340]
Fluid specifications
Ratings and data are based on operation with premium petroleum-based hydraulic fluids containing
oxidation and foam inhibitors.
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Technical specifications
Parameter Unit Minimum Continuous Maximum
Viscosity mm2/sec (cSt)
[SUS]
Temperature °C [°F] -40 [-40] 104 [220] 115 [240]
Cleanliness ISO 4406 Class 22/18/13 or better
Filtration efficiency suction filtration β35-44=75 (β10≥2)
charge filtration β15-20=75 (β10≥10)
7
[47]
12-60
[66-278]
1600
[7500]
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Initial start-up procedure
General
Start-up procedure
Follow this procedure when starting-up a new pump installation or when restarting an installation in
which the pump was removed.
Warning
Unintended movement of the machine or mechanism may cause injury to the technician or bystanders.
To protect against unintended movement, secure the machine or disable/disconnect the mechanism
while servicing.
Prior to installing the pump, inspect for shipping damage.
1. Ensure that the hydraulic fluid and system components (reservoir, hoses, valves, fittings, and heat
exchanger) are clean and free of contamination.
2. Install new system filter element(s) if necessary. Check that inlet line fittings are properly tightened
and there are no air leaks.
3. Install the pump. Install a 50 bar [1000 psi] gauge in the charge pressure gauge port M
4. Fill the housing by adding filtered fluid in the upper case drain port. Open the case plug in the top of
the control to assist with air bleed.
5. Fill the reservoir with hydraulic fluid of the recommended type and viscosity. Use a 10-micron filler
filter. Fill inlet line from reservoir to pump.
6. Disconnect the pump control input signal.
After start-up the fluid level in the reservoir may drop due to filling of the system components. Check
the level in the reservoir to maintain a full fluid level throughout the start-up procedure.
Caution
Damage to hydraulic components may occur from failure to maintain fluid supply.
7. Use a common method to disable the engine to prevent the engine from starting. Crank the starter
for several seconds. Do not to exceed the engine manufacturer’s recommendation. Wait 30 seconds
and then crank the engine a second time. This operation helps remove air from the system lines. Refill
the reservoir to recommended full fluid level.
8. When charge pressure reaches 3.5 bar [50 psi], enable and start engine. Let the engine run for a
minimum of 30 seconds at low idle to allow the air to work itself out of the system. Check for leaks at
all line connections and listen for cavitation. Check for proper fluid level in reservoir.
Caution
Air entrapment in fluid under high pressure may damage hydraulic components.
Do not run at maximum pressure until system is free of air and fluid has been thoroughly filtered.
9. When adequate charge pressure is established (as shown in model code), increase engine speed to
normal operating rpm to further purge residual air from the system.
10. Shut off the engine. Connect the pump control signal. Start the engine, checking to be certain the
pump remains in neutral. Run the engine at normal operating speed and carefully check for forward
and reverse control operation.
11. Continue to cycle between forward and reverse for at least five minutes to bleed all air and flush
system contaminants out of loop.
Normal charge pressure fluctuation may occur during forward and reverse operation.
12. Check that the reservoir is full. Remove charge pressure gauge. The pump is now ready for operation.
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Pressure measurement
Required tools
You can perform the service procedures described in this manual using common mechanic’s tools.
Special tools, if required are shown. Use calibrated pressure gauges to ensure accuracy. Use snubbers to
protect pressure gauges.
Port locations and gauge installation
The following sections list the ports for each type of hydraulic unit. The fitting size and recommended
pressure gauge are also specified.
The following table and drawings show the port locations and gauge sizes needed.
Port information
Port identifier Pressure obtained Gauge size Port size
M1, M2 System pressure 1000 bar [10 000 psi] 9/16-18
M3 (M6) Charge pressure 50 bar [1000 psi] 9/16-18
M4, M5 Servo pressure 50 bar [1000 psi] 9/16-18
L1, L2 Case pressure 10 bar [100 psi] 030-042 7/8-14
X1, X2 HDC/EDC control pressure 50 bar [1000 psi] 7/16-20 or 9/16-18
X3 External control pressure 50 bar [1000 psi] 9/16-18
S Charge pump inlet Vacuum gauge,
Tee into inlet line
055-100 1-1/16-12
130 1-5/16-12
180-250 1-5/8-12
030-042 1-1/16-12
055-075 1-5/16-12
100-180 1-5/8-12
250 1-1/2 SAE-split flange
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