Danfoss Series 20 User manual

powersolutions.danfoss.com
Service Manual and Repair Instructions
Axial Piston Pumps
Series 20
Hydrostatic Pump Repair
www.hydrostaticpumprepair.net
Phone: [phone]
Email: [email protected]

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 20142
The purpose of this manual is to provide you with the information necessary for the normal
maintenance and servicing of the Danfoss hydrostatic series 20 units.
This includes a description of the units and their components as well as troubleshooting, pressure
setting and repair procedures.
Minor repairs may be performed without affecting the warranty. Major repairs performed during the
warranty time could eventually affect the warranty.
To facilitate easy servicing, the unit has been designed with this in mind.
Many of the individual parts and assemblies are interchangeable throughout the entire series 20
family. This includes such items as the servo valve, the charge pumps and the manifold components.
In addition, many repairs and adjustments can be performed without having to remove the unit from
the vehicle, provided that the unit is easily accessible and a thorough cleaning of the unit is possible
before beginning with repairs.
Dirt or other forms of contamination are in most cases the reason for the breakdown of a hydraulic
unit. Please pay attention to cleanliness, not only when making repairs, but also when putting the
unit into operation, changing the oil, changing filters or any other procedures.
The following manual will provide you with comprehensive instructions for preventative
maintenance and recognition of causes of failure of the axial-piston units.
Danfoss axial piston variable displacement pumps are of swash plate design with variable flow
capability suitable for hydrostatic transmissions with closed loop circuit.
Tilting the swash plate to the opposite side of the neutral or zero displacement position reverses flow
direction.
The full-length shaft with a highly efficient tapered roller bearing arrangement offers a high loading
capacity for external radical forces.
The hydro-mechanical servo displacement control maintains the selected swash plate position and
hence pumps displacement.
Upon release of the control handle, the swash plate automatically returns to zero position and the
flow reduces to zero.
High case pressures can be achieved without leakage even at the lowest temperatures by using
suitable shaft seals.
The servo valve arrangement offers the facility to incorporate function regulators and remote control
systems.
Axial piston units are designed for easy servicing. Complete dismantling and reassembly can be
carried out with standard hand tools, and all components or sub-assemblies are replaceable.
Introduction
Description
General Description

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 2014 3
Contents
Model Code
Recommended Tools and
Installation
Start-up procedure
System Maintenance
Trouble Shooting
Disassembly and Assembly
Model Code................................................................................................................................................................................. 4
Tools for Minor Repairs and Unit Maintenance ............................................................................................................. 5
Additional Tools for Complete Stripping of Units......................................................................................................... 5
Measurement Instruments.................................................................................................................................................... 5
Trouble Shooting, Gauge Installation and Information.............................................................................................. 6
Preconditions for Trouble-free Operation....................................................................................................................... 7
First-time Operation................................................................................................................................................................. 8
Plumbing Installation (Variable Displacement Pump - Fixed Displacement Motor) ..................................... 10
System circuit Description................................................................................................................................................... 10
Inlet Filter .................................................................................................................................................................................. 11
Changing the oil...................................................................................................................................................................... 11
Leak Test ..................................................................................................................................................................................... 11
Cleanliness................................................................................................................................................................................. 11
Checking the oil level ............................................................................................................................................................ 11
Recommended oils................................................................................................................................................................. 11
Transmission Operates in one Direction Only.............................................................................................................. 12
System response is sluggish ............................................................................................................................................... 12
Neutral Difficult or Impossible to Find............................................................................................................................ 13
System will not Operate in either Direction.................................................................................................................. 13
Inspection Instructions ........................................................................................................................................................ 14
Checking the servo valve (control valve) ................................................................................................................. 15
Sectional View.......................................................................................................................................................................... 16
Axial piston variable displacement pump............................................................................................................... 16
Exploded View ......................................................................................................................................................................... 17
Minor repairs............................................................................................................................................................................. 18
Mounting block ................................................................................................................................................................. 18
Changing the shaft seal (disassembly)...................................................................................................................... 19
Changing the shaft seal (assembly) ...........................................................................................................................20
Changing the charge pump and the charge check valves................................................................................ 21
Changing the servo valve (control valve).................................................................................................................23
Major repairs............................................................................................................................................................................. 24
Changing the valve- and bearing plate (disassembly) ....................................................................................... 24
Changing the valve- and bearing plate (assembly) .............................................................................................25
Changing the cylinder block kit (disassembly)...................................................................................................... 27
Changing the cylinder block kit (assembly)............................................................................................................ 28
Changing the swash plate and servo piston (disassembly).............................................................................. 29
Changing the swash plate and servo piston (assembly).................................................................................... 31
Changing the pump shaft ............................................................................................................................................. 33
Installation Torque Values.................................................................................................................................................... 35

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 20144
Model Code
Producer mark
A1 producer specification
according to construction
(at present = A1)
S P V 2 A 1
Series of product
SPV Pump variable
2 Association
type 20
Orientation of rotation
R Right
L Left
Input port
working port SAE-flange
3= 3000 psi SAE J518 (207 bar)
for displacement 033 - 119 cm3
6= 6000 psi SAE J518 (414 bar)
for displacement 166 - 334 cm3
Displacement cm3[in3]
033 = 33.3 [2.03]
052 = 51.6 [3.15]
070 = 69.8 [4.26]
089 = 89.0 [5.43]
119 = 118.7 [7.24]
166 = 165.8 [10.12]
227 = 227.3 [13.87]
334 = 333.7 [20.36]
Shaft end
SAE-spline shaft 16/32
= 21 teeth for displacement 033 - 070
Z= 23 teeth for displacement 089
= 27 teeth for displacement 119 - 227
= 40 teeth for displacement 334
K* conic shaft end with toleranced key
* available on request
Units with working mark
3-letter combination e.g.:
Cxx All seals in Viton make
Special copies with or without
mark of copy:
037 3-letter combination e.g.
special nameplate
and all seals in Viton
Regulation
Type of regulation of 3-letter combination
001 - 999 Designation for regulation specification
(specified by manufacturer)
RNU… Pressure regulator of zero throw
RNO… Pressure regulator Mooring
RBR… Torque limiter
RBN… Torque limiter
with regulator of zero throw
RBN… Torque limiter
with pressure regulator Mooring
FBA… Mobile automation for frame size 033-119
End cap execution
PS… With installed charge pump
AA 10. Cover plate without gear pump
Filling gear pump (2 digits according to size) - see the table
Frame size Optional PS Frame size Optional PS
033 12 18 119 19 33
052 12 18 166 33 66
070 18 12 227 33 66
089 18 12 334 66
..3 Designation for setting of charge pressure 13 bar
(other setting of charge pressure on request)
Restriction of flow volume
The entry is required if the flow volume is
adjustable at least in one direction
1. Mark (3-characters) for the branch A
2. Mark (3-characters) for the branch B
Delimitation of flow volume is set
060 for example to 60 cm3
999 maximal setting of flow volume
950 without setting of flow volume
Control
Type of control is 3-letter combination
1-9 Type variant is 1-digit number
(is specified by manufacturer)
01-99 Designation for control and connecting plate
(is specified by manufacturer)
VML 1 Mechanical-hydraulic volume control
no entry Execution with control jet
VES 3 Electro-hydraulic volume control
VED 3 Electro-hydraulic 3-position control NG 6
VHA Setting hydraulic volume control by load control pressure
VAE 1 Connecting plate for supply and drain
of control liquid without control instrument
VAD 100 Without control instrument with segment
and with cover plate
Example of ordering:
Axial piston variable pump SPV 2,
Displacement 89,0 cm3, Orientation of rotation: right,
Input: flange 3000 psi, SAE shaft end 23 teeth,
End cap execution: with installed charge pump
Order mark: SPV 2 / 089 - R3Z - PS 183 -A1

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 2014 5
Tools for Minor Repairs and
Unit Maintenance
Additional Tools for
Complete Stripping of Units
Measurement Instruments
1 Circlip pliers ∅2 to 2.5 mm
1 Screw driver 3 mm
1 Screw driver 6 mm
1 Screw driver 9 mm
1 Plastic hammer - small
1 Pointed pliers (can also be slightly bent)
1 Torque key to 14.9 Nm [132 lbf•inch]
1 Set of ring spanners 5/16 to 11/4
1 Set of Allenkeys 1/4to 3/8
1 Fixed spanner 15/6for high pressure relief valve
1 Puller retainer seal
(Major repairs should not be carried out during the warranty period.)
1 Right angle screw driver 16 mm
1 Set of drifts 2 to 10 mm
1 Plastic hammer - large
1 Bearing puller 80 x 120 mm
1 Bearing puller 200 x 250 mm
1 Each fixed spanner for servo cylinder 36, 41, 46, 50, 55, 60, 65 mm
1 Depth gauge 300 mm
1 Set of fixed or open ended spanners 7/16 to 11/4
1 Fitting block - see page 14
At last 2 pressure gauges up to 60 bar damped (charge pressure - servo pressure)
1 Vacuum gauge to +1.0 ÷-1.0 bar [14.5 ÷-14.5 psi] (vacuum measurement at the charge pump)
2 Pressure gauges to 600 bar [8700 psi] (high pressure measurement at the valve
block)
1 Pressure gauge to 8 bar [116 psi] (casing pressure measurement)
Additional: Torque spanners, separate order!
Recommended Tools and
Installation

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 20146
Trouble Shooting, Gauge
Installation and Information
Recommended Tools and
Installation
Gauge Information
ACharge Pressure 60 bar [870 psi] - Gauge 7/16 - 20 UNF O-ring Fitting
BSystem pressure 600 bar [8700 psi] - Gauge 7/16 - 20 UNF O-ring Fitting
CInlet Vacuum Vacuum gauge Tree Into Inlet Line
DCase pressure 8 bar [116 psi] - Gauge Adapt to Bottom Drain Port

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 2014 7
Preconditions for Trouble-
free Operation
Cleanliness: Ensure that the pipes, pipe connections and hoses as well as all other components are
completely clean.
Ventilation and venting of the oil reservoir via an air filter.
Operating fluid: HLP fluid according to DIN 51524, ATF type A SUFFIX A, HD-SAE motor oils, see Fluid
Manufacturers, Technical Information.
Oil level: (The inlet pipe and return flow port must always be below the surface of the oil).
No funnel-shaped eddying at the inlet connection pipe. No formation of foam at the return flow pipe.
The inlet connection pipe must be substantially above the bottom of the reservoir. A partition plate
should be located between the inlet and return flow connection pipes.
Filtration
Filtration grade = 10 µm [394 µinch] nominal.
Inlet pressure of charge pump: 0.85 bar [12.3 psi] absolute (- 0.15 bar [-2.2 psi]) with a new filter
element and at an operating temperature of approx. 50 °C [122 °F].
A charge pump inlet pressure less than 0.75 bar [10.9 psi] absolute (-0.25 bar [-3.6 psi]) is permissible
for a short time with a reservoir temperature of less than 50 °C [122 °F] on a cold start in order to warm
up the system under no-load.
If frequent cold starts are to be made, the system should be warmed up by a reservoir heater.
If the charge pump inlet pressure is less than 0.75 bar [10.9 psi] absolute (-0.25 bar [-3.6 psi]) on
operating temperatures higher than 50 °C [122 °F], the filters must be changed.
A charge pump inlet pressure of less than 0.5 bar [7.3 psi] absolute (- 0.5 bar [-7.3 psi]) is not
permissible.
The filter requires changing or the operating temperature is too low.
Venting the pump and motor housing as well as the connection lines and other components.
The return flow to the oil reservoir must be free of bubbles. After venting the system, check the fluid
level and fill to proper level if necessary.
Carry out a leak test on the transmission (inlet line, filter, pipe and hose lines, valves, control
elements, pump and motor) giving due consideration to the service life of the transmission,
environmental protection and the reduction of oil consumption.
Tighten up any leaking joints and other connections while the system is not under pressure.
Pressure fluid temperature range: min. = -40 °C [-40 °F], max. = 95 °C [203 °F].
Viscosity range:
max. = 1000 mm2/s [4630 SUS*] (cSt) (for a short time only on a cold start).
min. = 7 mm2/s [49 SUS*] (cSt).
Recommended viscosity range: 12-60 mm2/s [66-278 SUS*] (cSt).
*SUS (Saybolt Universal Second)
Changing the oil: The oil should be changed after max. 80-100 hours of operation, but at the latest
one year after first-time operation.
The second oil change should be after max. 500 hours of operation but at the latest one year after the
first change of fluid.
Thereafter, the oil should be changed every 1000 hours of operation but at least once a year. It is not
permissible to mix oil.
Renew the inlet filter each time the oil is changed or when the inlet pressure of the charge pump
falls below the permissible tolerance.
Clean the air filter whenever too much dirt has accumulated.
The max. speed is as specified in the catalogue Series 20 Axial Piston Pumps, Technical Information or
Series 20 Axial Piston Motors, Technical Information.
Start-up procedure

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 20148
Preconditions for Trouble-
free Operation (continued)
First-time Operation
The charge pressure measured at the charge pressure gauge connection port of the pump with the
adjusting lever in the neutral position should be approx. 15 bar [217.6 psi] at a pump input speed n =
1500 min-1 (rpm).
The charge pressure measured at the charge pressure gauge connection port of the pump with the
adjusting lever engaged should be approx. 2 bar lower at a pump input speed n = 1500 min-1 (rpm).
1. After installing the transmission and the corresponding pipeline connections, remove the plug
from the charge pressure gauge port of the variable displacement pump. Fit a gauge with a
measuring range up to 60 bar [870 psi] to this port.
The charge pressure gauge port has a straight 7/16-20 UNF-2 B SAE thread.
2. Disconnect the charge pump inlet line from the charge pump inlet connection pipe.
3. Fill the pump case and the motor case with the recommended oil through the drain port.
4. Fill the oil reservoir with fluid. As soon as oil emerges from the end of the disconnected charge
pump inlet line tighten the pipe connector (see table to page 35 for the correct tightening torque)
and continue to fill the reservoir.
Only use oil reservoirs that are fitted with air filters.
5. Disconnect the control linkage from the control handle.
The pump must be in the zero position.
6. Allow the prime mover to turn for approx. 15 sec. by using the starter.
If the prime mover is an electric motor: Switch on and off again.
7. Then start the prime mover and allow the pump to turn at idling speed (approx. 750 min-1) for
approx. 5 minutes.
In the case of electric prime mover: Allow to turn for approx.1 minute.
After initial fluctuations in pressure, the charge pressure should settle down to 10 bar [145 psi] or
12 bar [174 psi].
8. Check the pressure fluid level.
9. Raise the speed to approx. 1500 min-1 (rpm). The gauge should now indicate a pressure of approx.
15 bar [217.6 psi].
10. If the charge pressure falls to below 8 bar [116 psi], stop the prime mover, find the fault in
accordance with the trouble-shooting guide and take the appropriate remedial action.
Start-up procedure

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 2014 9
First-time Operation
(continued)
P000 337E
Gauge port -
servo cylinder pressure
(both side)
Control handle
Gauge port "M":
Charge pressure
Port "S":
Suction port
(charge pump)
Port "A"+"B":
High pressure
Case drain ports
11. Stop the prime mover and attach the control linkage to the control handle. Check the fluid level in
the sight glass and fill to proper level if necessary.
12. Restart the prime mover and, under no-load, adjust the zero position by means of the control
handle - or even better by the control linkage - so that in both directions final position of stroke
per Series 20 Axial Piston Pumps, Technical Information is achieved.
13. Allow the prime mover to turn at 1500 min-1 (rpm). The charge pressure should now be 15 bar
[217.6 psi].
14. Slowly move the control handle backwards and forwards. If the pump is working properly, the
charge pressure drops by about 2 bar [29 psi] from the value stated in step 13 above as the control
handle initiated.
15. Allow the system to work under full load with a pump speed of approx.1500 min-1 (rpm). It must
be possible to achieve the values stated in steps 13 and 14 above.
16. Check all joints and connections for leaks.
17. Stop the prime mover. Remove the gauge from the connection port. Replace the 7/16-20 UNF-2 B
plug and tighten with the tightening torque stated in the table to page 35.
Check the pressure fluid level in sight glass of the reservoir and fill to proper level if necessary.
The system is now ready for operation.
Start-up procedure

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 201410
P000 341
Plumbing Installation
(Variable Displacement
Pump – Fixed Displacement
Motor)
System circuit Description
Start-up procedure
HEAT EXCHANGER BYPASS VALVE
RESERVOIR
VACUUM GAUGE
HEAT EXCHANGER
OUTPUT SHAFT
MOTOR SWASHPLATE
FIXED
DISPLACEMENT MOTOR
LOOP FLUSHING VALVE
PURGE RELIEF VALVE
CHARGE PRESSURE
RELIEF VALVE
SERVO
PRESSURE
RELIEF VALVES
SERVO CONTROL CYLINDER
SERVO CONTROL CYLINDER
PUMP SWASHPLATE
REVERSIBLE VARIABLE
DISPLACEMENT PUMP
CONTROL
HANDLE
INPUT SHAFT
WORKING LOOP (LOW PRESSURE) SUCTION LINE CASE DRAIN FLUIDCONTROL FLUIDWORKING LOOP (HIGH PRESSURE)
P000 027E

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 2014 11
The filter element must be exchanged as soon as the pressure drops below 0.75 bar [10.9 psi]
absolute (-0.25 bar [-3.6 psi]) when the transmission is at normal operating temperature. The filter
must also be exchanged each time the pressure fluid is changed. Filtration grade = 10 µm [394 µinch]
nominal.
Under normal operating conditions, the oil should be changed at the following intervals:
The first oil change should be carried out after max. 80-100 hours of operation but at the latest one
year after first-time operation. The second change should take place after max. 500 hours of
operation but at the latest one year after the first change.
Thereafter, the oil should be changed at least every 1000 hours of operation or at least once a year.
To change the oil, the used fluid must be drained off when the system is at operating temperature!
Remove any residual dirt or sludge from the reservoir!
In extremely dusty atmospheres, the intervals between oil changes must be correspondingly
shortened.
Oil samples should be taken every 500 hours of operation. To do this, take approx. 0.5l of oil from a
point on a level with the inlet (suction) connection. Fill the sample into a closable container that is
free of residues.
Have the oil examined for serviceability by Danfoss, by Oil Manufacturer or by an appropriate
institution.
Important: Use only recommended oils! (See Fluid Manufacturers, Technical Information). It is not
permissible to mix oils.
Carry out a leak test on the transmission (inlet line, filter, pipe and hose lines and connections, valves,
control elements, pump and motor) giving due consideration to the service life of the transmission,
environmental protection and reduction of oil consumption.
Tighten up any leaking joint and other connections while the system is not under pressure.
Make certain that the air filter for ventilation of the oil reservoir is regularly cleaned, since the input
pressure may be affected if it is dirty. If there is an oil cooler, the cooler surface should be kept free
from contamination. On units which have hose couplings on the connecting pipes, contamination of
any sort must be avoided. Cotton rags or lint cleaning cloths may not be used for cleaning. Use only
lint-free materials.
When changing the oil, be sure the area around the filler cap is free from foreign objects. The oil,
which can be kept clean by using a filter cloth, should be added by means of a clean funnel.
The level of the oil should be checked daily using the gauge glass. In case of loss of oil, the leak must
be rectified.
Important: Use only recommended fluids! (See Fluid Manufacturers, Technical Information.) It is not
permissible to mix.
HLP - hydraulic fluids according to DIN 51524
ATF - automatic transmission fluids type A, SUFFIX A
HD - SAE motor oils
Inlet Filter
Changing the oil
Leak Test
Cleanliness
Checking the oil level
Recommended oils
System Maintenance

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 201412
Check control
linkage
Repair
or replace
Inspect high pressure
relief valve
(see Series 20 Axial Piston
Motors, Service Manual
and Repair Instruction)
Insert charge
check valves
(see page 14)
Repair
or replace
(see page 21,22)
Inspect shuttle valve
in valve block
(see Series 20 Axial Piston
Motors, Service Manual
and Repair Instruction)
Repair or replace
the valve block
(see Series 20 Axial Piston
Motors, Service Manual
and Repair Instruction)
OK
DefectiveDefective
OK OK
Inspect control valve
(see page 15)
Replace control valve
(see page 23)
Defective
Defective Defective
OK
Repair or replace
(see Series 20 Axial Piston
Motors, Service Manual
and Repair Instruction)
Check charge
pressure
(see page 14)
Inspect
control valve
(see page 15)
Inspect motor
by-pass valve
(if used)
Replace
control valve
(see page 23)
OK
Defective
OK
OK
Repair
or replace
Defective
Replace
transmission
(pump+motor)
OK
Inspect charge
pressure
relief valve
(see page 14)
Repair
or replace
(see page 21, 22)
Inspect purge
relief valve at motor
(see Series 20 Axial Piston
Motors, Service Manual
and Repair Instruction)
Inspect charge
pressure
relief valve
(see page 14)
Repair or replace
the valve block
(see Series 20 Axial Piston
Motors, Service Manual
and Repair Instruction)
DefectiveDefective
Repair
or replace
(see page 21, 22)
Defective
Inspect
inlet filter
OK OK
Replace
Clogged
Inspect
charge pump
(see page 14)
Repair
or replace
(see page 21, 22)
Defective
to low
in
neutral
to low in neutral and
forward or reverse
to low inforward
or reverse
System response is sluggish
Transmission Operates in
one Direction Only
Troubleshooting

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 2014 13
Neutral Difficult or
Impossible to Find
System will not Operate in
either Direction
Check control
linkage
Repair
or replace
Inspect control valve
(see page 15)
Replace
pump
Replace control valve
(see page 23)
OK OK
DefectiveDefective
Check fluid
level in
reservoir
Check control
linkage
Inspect motor
by-pass valve
(if used)
Repair
or replace
OK
Defective
OK
Fill to
propper level
to low
Repair
or replace
Defective
Check charge
pressure
(see page 14)
OK
Inspect
charge pump
(see page 14)
Inspect
inlet filter
Repair
or replace
(see page 21, 22)
Defective
Replace
Defective
Inspect charge
pressure
relief valve
(see page 14)
Repair
or replace
(see page 21, 22)
Clogged
Inspect purge
relief valve at motor
(see Series 20 Axial Piston
Motors, Service Manual
and Repair Instruction)
Repair or replace
the valve block
(see Series 20 Axial Piston
Motors, Service Manual
and Repair Instruction)
Defective
Replace
transmission
(pump + motor)
Inspect
control valve
(see page 15)
Replace
control valve
(see page 23)
Defective
Inspect motor
by-pass valve
(if used)
Repair
or replace
Defective
Check system
pressure
(see Series 20 Axial Piston
Motors, Service Manual
and Repair Instruction)
to low in
neutral and
forward or
reverse to low in
forward or
reverse
to low in
neutral
OK
OKOK OK
OK OK OK
Troubleshooting

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 201414
Checking the charge pressure
Checking the charge pump
Checking the charge check valves
1. Remove charge pump to examine check
valves (see page 21).
1. Inspect if contamination is holding the valve
open and for galling or wear on valve cone
and seat and inspect for broken spring.
2. The shaft and gear teeth must work freely.
3. Further disassembly of the charge pump is not
permitted.
2. Check the spring pressure and for correct
operations. Check if contamination may be
prohibiting free movement of the ball.
Inspection Instructions
F000 077
F000 078
F000 079 F000 080
Hex-plug, Spring 3
Shims Valve cone
5+6 10 5+6
Troubleshooting
1. Clean the charge pressure gauge connection
on the pump.
2. Pressure gauge (see recommended measuring
instruments) to be connected.
3. Set operating speed at 1500 min-1
4. Charge pressure with the pump in neutral ca.
15 - 18 bar [218 - 261 psi]. When the pump in
forward or reverse the charge pressure should
be at a two bar lower level (purge relief valve,
motor).

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 2014 15
1. Disconnect the external control linkage from
the control handle and check for neutral
operating with control handle. Releasing
control handle should allow the pump to
return to neutral. If operation is satisfactory
with external control linkage disconnected,
the problem is not in the hydrostatic
transmission.
If operation is not satisfactory with external
control linkage disconnected from control
handle, the control may be misadjusted.
3. Holding the control in place, and swing it
away from housing and remove. Inspect
visible linkages, torsion spring, and O-rings.
Inspect for missing, plugged, or incorrect
orifice.
Checking the servo valve (control valve)
Trouble Shooting
2. Remove the cap screws (see page 22).
4. Further disassembly of servo valve is not
permitted.
Inspection Instructions
(continued)
F000 082
F000 083
F000 046
F000 062
86 89, 90 82
86 78 Orifice (81) 81 85 80 86 87 88

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 201416
Disassembly and Assembly
Sectional View
Input shaft
Swash plate Control handle Servo valve (control valve)
Charge pump
Charge check valve
Servo cylinder
Cylinder block assembly
Shaft seal
P005 121E
Axial piston variable displacement pump

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 2014 17
Description of parts:
1 Hexagonal screw 28 Piston assembly 65 Hexagonal screw
2 Washer 29 Thrust plate 66 Washer
3 Charge pump assembly 30 Screw 67 Trunnion
4 Gasket charge pump 31 Sleeve retainer 68 Shim pack
5 Valve check 32 Servo sleeve complete 69 O-ring
6 O-ring 33 O-ring 70 Bearing
7 Hexagonal screw 34 O-ring 71 O-ring
8 Hexagonal screw 35 Screw 75 O-ring
9 Washer 36 Washer 77 Ring retaining
10 End cap 37 Spring guide 78 Gasket
11 Shim 38 Servo spring 80 O-ring
12 Gasket 46 Pin 81 Orifice
13 Bearing 47 Locking washer 82 Kit control valve
14 Cylindrical pin 48 Connecting link 85 Spacer control servo
15 Valve plate 49 Shaft 86 Handle control handle
16 Bearing plate 50 Bearing 87 Lock washer tooth
17 Bearing plate pilot ring 51 Gasket 88 Nut hex
18 Ring retaining 52 Cylindrical pin 89 Washer
19 Retainer spring 53 Cover 90 Hexagonal screw
20 Spring guide 54 Washer 102 Hexagonal screw
21 Spring 55 Hexagonal screw 121 Orifice
22 Spring seat 59 O-ring 125 Orifice
23 Retainer spring 60 Plug 135 Swash plate complete
24 Cylindrical pin 61 Expander 145 O-ring
25 Cylinder block 62 Housing 146 O-ring
26 Retainer guide 63 O-ring 198 Cylinder block kit
27 Slipper retainer 64 Cylindrical pin 199 Shaft seal kit
Exploded View
P005 113
Disassembly and Assembly

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 201418
Ø10 Pin
[Ø0.394]
70
[2.756]
5x45°
20
[0.787]
10
[0.394]
ca. 5 mm Chamfer
[ca. 0.2 in]
Ø130
[Ø5.118]
165
[6.496]
250
[9.843]
250
[9.843]
P005 112E
The areas of repair indicated may be serviced, following the procedures in this manual, without
invalidating the warranty.
Preparation for assembly
When using a lifting device, the hooks at the end of the slings, are to be fastened in the rings fitted at
the front and rear of the motor body. It is recommended that an mounting block should be used in
order to facilitate a professional operation.
Mounting block
Disassembly and Assembly
F000 084
Minor repairs
F000 085

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 2014 19
Disassembly and Assembly
Minor repairs
(continued)
The seal-stationary is removed next. It is held in
place by the friction of the O-ring on its O. D.
Remove seal-stationary with the help of a seal
puller to prevent damage to outer edge.
CCAUTION!
These parts can be easily damaged. Use care in
handling. Each part should be inspected
separately if parts are to be reused.
Always replace the O-rings.
Lubricate the small O-ring with petroleum jelly
and insert into the I. D. of the bronze rotating
ring.
Lubricate the large O-ring and place the O. D. of
the seal-stationary.
It is recommended that all shaft seal parts be
replaced. If parts are to be reused, they must be
protected from being damaged by the shaft
during removal. Remove the large retaining ring
located on the shaft end of the pump.
Remove the side opposite the tangs from the
groove first.
The rotating seal ring (bronze ring) is also held in
its position by the O-ring. It can be removed with
the help of two screw drivers.
F000 086
F000 088
F000 087
Changing the shaft seal (disassembly)
77
71 Bronze ring
77 75 Seal-
stationary
77 Clamp seal puller
on seal-stationary

Service Manual and Axial Piston Pumps Series 20
Repair Instructions
L1003506 • Rev BA • Jun 201420
Changing the shaft seal (assembly)
Slide seal-stationary into place against the
bronze sealing ring.
Slide the bronze sealing ring over the shaft and
onto the shaft pilot diameter with the O-ring
facing the unit. Work the ring into place using
hand force only.
CCAUTION!
Protect parts from damage by the shaft.
Compress the seal-stationary to expose the
retaining ring groove. Install the retaining ring
with the beveled side out, putting the side
opposite the tangs into the groove first. Be
certain that the retaining ring has snapped into
the groove completely.
F000 089
F000 213
F000 091
F000 090
71 Bronze ring
Seal stationary
77 Clamp seal puller
on seal-stationary
77
Disassembly and Assembly
Minor repairs
(continued)