Danfoss T90 Series User manual

Service Manual
Series T90 Axial Piston Pumps
www.danfoss.com

Revision history Table of revisions
Date Changed Rev
March 2020 1st editiom 0101
Service Manual
Series T90 Axial Piston Pumps
2 | ©Danfoss | March 2020 AX216086485386en-000101

Introduction 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.............................................................................................................................................................................9
The basic closed circuit.............................................................................................................................................................9
Case drain and heat exchanger..............................................................................................................................................9
Operation T90 charge pump operation......................................................................................................................................................12
T90 charge relief valve operation.............................................................................................................................................12
T90 multi-function valve operation.........................................................................................................................................12
T90 pressure limiter/high pressure relief valve operation..............................................................................................13
T90 system check valve operation...........................................................................................................................................13
T90 bypass valves operation......................................................................................................................................................13
T90 speed sensor operation.......................................................................................................................................................14
T90 filtration options.................................................................................................................................................................... 14
T90 MDC operation....................................................................................................................................................................... 14
T90 MDC solenoid override valve operation........................................................................................................................15
Neutral start switch (NSS) for MDC..........................................................................................................................................15
T90 HDC operation........................................................................................................................................................................15
T90 3-Position (FNR) electric control operation..................................................................................................................15
High Current Electrical Displacement Control (HCEDC).................................................................................................. 15
HCEDC Principle........................................................................................................................................................................15
HCEDC Operation.....................................................................................................................................................................16
Manual OverRide (MOR)..............................................................................................................................................................16
Operating parameters T90 Input speed..............................................................................................................................................................................18
T90 system pressure......................................................................................................................................................................18
T90 charge pressure......................................................................................................................................................................18
T90 charge inlet pressure............................................................................................................................................................19
Case pressure...................................................................................................................................................................................19
Temperature and viscosity......................................................................................................................................................... 19
Fluid and filter recommendations........................................................................................................................................... 19
Technical specifications Overview........................................................................................................................................................................................... 21
Features and options....................................................................................................................................................................21
Operating parameters..................................................................................................................................................................21
Fluid specifications........................................................................................................................................................................21
Initial start-up procedure General ..............................................................................................................................................................................................23
Start-up procedure........................................................................................................................................................................23
Pressure measurement Required tools.................................................................................................................................................................................24
Port locations and gauge installation.....................................................................................................................................24
Troubleshooting Overview........................................................................................................................................................................................... 26
Neutral difficult or impossible to find.....................................................................................................................................26
Service Manual
Series T90 Axial Piston Pumps
Contents
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System operating hot...................................................................................................................................................................26
Transmission operates normally in one direction only....................................................................................................26
System will not operate in either direction.......................................................................................................................... 27
Low motor output torque...........................................................................................................................................................27
Improper motor output speed..................................................................................................................................................27
System noise or vibration........................................................................................................................................................... 28
System response is sluggish...................................................................................................................................................... 28
Adjustments Standard procedures, inspections, and adjustments....................................................................................................... 29
Adjustments.....................................................................................................................................................................................29
Charge pressure relief valve adjustment...............................................................................................................................29
Multi-function valve pressure adjustment............................................................................................................................31
Engaging the bypass function.................................................................................................................................................. 32
Displacement limiter adjustment............................................................................................................................................ 33
Control Neutral Adjustment.......................................................................................................................................................34
Verify neutral setting...............................................................................................................................................................35
Servo Adjustment Side M4....................................................................................................................................................35
Standard manual displacement control (MDC) adjustment..........................................................................................36
MDC Neutral start switch (NSS) adjustments.......................................................................................................................36
Checking switch continuity........................................................................................................................................................40
Hydraulic displacement control (HDC) and electric displacement control (EDC) adjustment..........................41
Speed sensor adjustment........................................................................................................................................................... 42
Minor repair Standard procedures....................................................................................................................................................................43
Shaft seal and shaft replacement.............................................................................................................................................43
Multi-function valve cartridges.................................................................................................................................................46
Charge pressure relief valve.......................................................................................................................................................48
Adding an Auxiliary pad to a pump previously without one.........................................................................................50
Auxiliary pad....................................................................................................................................................................................51
Charge pump...................................................................................................................................................................................52
Integral charge pressure filter replacement.........................................................................................................................55
Pump control cover plate........................................................................................................................................................... 57
Displacement control orifices....................................................................................................................................................57
Displacement control orifice check valve............................................................................................................................. 58
Manual displacement control (MDC)......................................................................................................................................58
Solenoid override valve for MDC..............................................................................................................................................60
Solenoid override valve for MDC with pressure released brake...................................................................................60
Hydraulic and electric displacement controls.....................................................................................................................61
3-Position (FNR) electric control...............................................................................................................................................62
Displacement control filter screens.........................................................................................................................................64
Speed sensor................................................................................................................................................................................... 64
Control Module Repair.................................................................................................................................................................65
Replace control solenoids/actuator housing.......................................................................................................................67
Torque chart Fastener size and torque chart..................................................................................................................................................68
Plug size and torque chart..........................................................................................................................................................68
Fasteners and plugs......................................................................................................................................................................69
Service Manual
Series T90 Axial Piston Pumps
Contents
4 | ©Danfoss | March 2020 AX216086485386en-000101

Overview
This manual includes information for the installation, maintenance, and minor repair of Series T90 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.
Warranty
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.
Service Manual
Series T90 Axial Piston Pumps
Introduction
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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.
Service Manual
Series T90 Axial Piston Pumps
Introduction
6 | ©Danfoss | March 2020 AX216086485386en-000101

Symbols used in Danfoss literature
WARNING may result in injury Tip, helpful suggestion
CAUTION may result in damage to product or
property Lubricate with hydraulic fluid
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
specification
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.
Design
Danfoss Series T90 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.
Service Manual
Series T90 Axial Piston Pumps
Introduction
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Cross section
Slider block Servo piston Servo arm Piston Slipper
Feedback linkage
Roller bearing
Cradle bearing
Shaft seal
Input shaft
P400621
Cradle guideSwash plate
Charge pump
Rear bushing
Cylinder block
Bushing
Service Manual
Series T90 Axial Piston Pumps
Introduction
8 | ©Danfoss | March 2020 AX216086485386en-000101

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.
Basic closed circuit diagram
Input PV MF
Case drain line
Output
Flow (Bi-directional)
Reservoir
P104 120E
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.
Service Manual
Series T90 Axial Piston Pumps
Introduction
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System circuit diagram
Pump Motor
Working loop (low pressur e) 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 moto r
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 T90 Axial Piston Pumps
Introduction
10 | ©Danfoss | March 2020 AX216086485386en-000101

Pump schematic
P104 126E
M4
M5
L2
S
L1
X5
M1
M2
A
B
M3
Service Manual
Series T90 Axial Piston Pumps
Introduction
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T90 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
Case
drain
line Charge relief valve
Charge
pump
System
check
valves
Input
Inlet filter
Tank
PV PF
P104 121E
T90 charge relief 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
Charge pressure P106 157E
T90 multi-function valve operation
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 T90 pump to handle functions in
either direction. See corresponding sections for adjustments and repairs.
Service Manual
Series T90 Axial Piston Pumps
Operation
12 | ©Danfoss | March 2020 AX216086485386en-000101

Multi-function valve
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
Some multi-function valves do not include a pressure limiter valve
T90 pressure limiter/high pressure relief valve operation
Series T90 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
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
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.
T90 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.
T90 bypass valves operation
You can operate the bypass valves to move the vehicle or mechanical function when the pump is not
running. Manually resetting the valve position opens the valve. The bypass valves are built into the multi-
function valves.
Service Manual
Series T90 Axial Piston Pumps
Operation
©Danfoss | March 2020 AX216086485386en-000101 | 13

T90 speed sensor operation
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.
T90 filtration options
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
Charge pump Filter
Hydraulic fluid reservoir
Adjustable
charge pressure relief valve
To pump case
To low
loop and
control
Manometer
P102 003E
T90 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.
T90 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
To pump case
Charge pump
Hydraulic fluid reservoir
Filter
To low
pressure
side and
control
Screen
Adjustable
charge pressure
relief valve
P102 004E
T90 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.
Service Manual
Series T90 Axial Piston Pumps
Operation
14 | ©Danfoss | March 2020 AX216086485386en-000101

T90 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.
T90 HDC operation
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.
T90 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.
P003 191
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
Service Manual
Series T90 Axial Piston Pumps
Operation
©Danfoss | March 2020 AX216086485386en-000101 | 15

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.
HCEDC schematic
Feedback from
Swash plate
PTF00B
M14
1C2C
F00A
P003 478E
A serviceable 125 μm screen is located in the supply line immediately before the control porting spool.
HCEDC Operation
T90 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.
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 spring-
loaded servo piston will automatically return the pump to the neutral position.
Manual OverRide (MOR)
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.
W
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.
Service Manual
Series T90 Axial Piston Pumps
Operation
16 | ©Danfoss | March 2020 AX216086485386en-000101

P003 204
MOR Schematic diagram (EDC shown)
C1C2
P108758
Service Manual
Series T90 Axial Piston Pumps
Operation
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T90 Input speed
There are three acceptable input speeds that the T90 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.
W
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.
T90 system 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.
T90 charge pressure
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.
Service Manual
Series T90 Axial Piston Pumps
Operating parameters
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T90 charge inlet pressure
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.
Case pressure
Under normal operating conditions, do not exceed the rated case pressure. During cold start, maintain the
case pressure below maximum intermittent case pressure.
C
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 and viscosity
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.
Service Manual
Series T90 Axial Piston Pumps
Operating parameters
©Danfoss | March 2020 AX216086485386en-000101 | 19

Fluid and filter change interval
Reservoir type Max oil change interval
Sealed 2000 hours
Breather 500 hours
C
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.
Service Manual
Series T90 Axial Piston Pumps
Operating parameters
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