Service guide
PAH pumps
PAH 20-32
Disassembling and assembling
hpp.danfoss.com
Service guide | Disassembling and assembling PAH 20-25-32
Table of Contents 1. Disassembling the pump ................................................................................................................... 3
2. Inspection ............................................................................................................................................ 7
2.1. Port plate and thrust plate ................................................................................................................. 7
2.2. Pistons .................................................................................................................................................... 7
2.3. Cylinder barrel ..................................................................................................................................... 8
2.4. Housing .................................................................................................................................................. 8
2.5. Swash plate .......................................................................................................................................... 8
3. Assembling ...........................................................................................................................................9
4. Service kit list for PAH 25-32 ............................................................................................................14
5. Exploded view PAH 25-32 ................................................................................................................ 15
Introduction
NOTE: If the pump is disassembled within the warranty period, the pump is no longer covered
by the warranty.
This document covers the instructions for
disassembling and assembling the axial piston
pumps PAH 20-25-32
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180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
Service guide | Disassembling and assembling PAH 20-25-32
1. Disassembling the
pump
2. Remove the parallel key and unscrew the
front cover.1. Tools required for dismantling.
3. Unscrew the screws in the front ange. 4. Remove the front ange.
4. Remove the shaft seal using two
screw drivers.
Caution: Avoid scratching the sealing
surface on the shaft.
6. Remove the guide pin from the housing
and the two guide pins from the
swash plate.
180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
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Service guide | Disassembling and assembling PAH 20-25-32
7. Remove the swash plate using the front
screw.
8. Remove the cylinder barrel from the
housing.
10. Separate the housing and the end cover.9. Unscrew the six screws in the end cover.
12. Remove the guide pins and the guide.11. Remove the valve plate from the end cover.
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180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
Service guide | Disassembling and assembling PAH 20-25-32
14. Remove the retaining plate.13 Remove the pistons.
15.Remove the retaining ball.
17. Remove the ceramic ring from the front
ange.
16. Remove the the thrust plate using two
screwdrivers.
18. The ceramic ring removed from the front
ange.
180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
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Service guide | Disassembling and assembling PAH 20-25-32
Housing with
bearing
Front Flange
Port ange
19. Wash all parts and replace all seals
(inclusive shaft seal).
21. If the pump has failed, the reason for the
failure must be found and xed before the
repaired pump is re-installed.
20. Inspect all parts carefully (see ”Inspection”)
and replace any worn parts.
Cylinder barrel
Retainer plate
Port plate
Pistons
Thrust plate
with sealings
Washer and
screw (for xing
swash plate)
Screws for anges
Key
Five guide pins
Retainer ball
Retaining guide
Swash plate
Ceramic ring
Shaft seal
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180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
Service guide | Disassembling and assembling PAH 20-25-32
2. Inspection 2.1. Port plate and thrust plate
1. Neither port plate nor thrust plate must
show any sign of wear.
2. Hold a ruler against the surface of the
plates and check the tightness against a
light source.
3. Check that both O-rings and back-up rings
are not broken and do not show severe
wear.
2.2. Pistons
1. The play in the ball and socket joint must
not exceed 0.1 mm.
2. The thickness of the piston shoes must be
at least 4.1 mm.
3. Hold a ruler against the surfaces of the
piston shoes to check that the surfaces
are even and smooth and without any
scratches.
4. It is acceptable that the (black) treated
surfaces of the pistons are partly worn.
180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
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Service guide | Disassembling and assembling PAH 20-25-32
2.3. Cylinder barrel
1. Check the outer bearing surface for large
wear grooves (not critical).
2.4. Housing
2. Check that the bushings are free from
seizure and large scratches.
3. Ensure that the pistons can move freely in
the bushings.
2. Check the bearing (the black part) for
large wear grooves (not critical).
2.5. Swash plate
1. Check that the surface of the swash plate
is smooth and without any large scratches
(depth more than 0.1 mm).
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180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
Service guide | Disassembling and assembling PAH 20-25-32
3. Assembling
WARNING:
Do not use silicone when assembling the
pump. Do not reuse disassembled O-rings;
they might be damaged. Always use new
O-rings.
1. Lubrication:
• To prevent seizing-up, lubricate all
threads with PTFE lubrication type.
• O-rings inside pump may be lubricated
only with clean ltered water.
• O-rings for port ange, mounting ange
and ushing valve must be lubricated.
• It is important to lubricate ALL parts to
be assembled with clean ltered water
(Especially all PEEK parts).
Important:
It is essential that the pump is serviced in
conditions of absolute cleanliness. All parts
must be absolute clean before mounting.
2. Parts and tools required for assembly.
Check that all parts are OK. Replace all
seals.
3. Mount the O-ring, the guide and the guide
pins on the port ange.
Guide pin
4. Mount the valve plate in its right position
using the pin as guide.
180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
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Service guide | Disassembling and assembling PAH 20-25-32
6. Mount the thrust plate with sealings on
the cylinder barrel.5. Mount the housing using the pin as guide.
7. Press the thrust plate into the cylinder
barrel using a table or the like as support.
9. Slide the retaining ball (smallest diameter
pointing upwards) down the shaft.
8. Mount the cylinder barrel in the housing.
10. Mount the retaining plate (smallest centre
diameter pointing upwards).
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180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
Service guide | Disassembling and assembling PAH 20-25-32
12. Mount the ceramic ring on the tool.11. Mount the pistons.
13. Mount the ceramic ring by pressing the
tool as far down in the front ange as
possible.
Washer
Spring
Shaft seal
15. Mount the shaft seal (carbon surface
pointing downwards), the spring, and the
washer (edge pointing downwards) by
sliding them over the tool.
14. Push the tool through the front ange.
16. Mount the swash plate on the front ange
using the pins as guide.
180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
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Service guide | Disassembling and assembling PAH 20-25-32
17. Press the swash plate against the ange
and screw the tools together. 18. Mount the O-ring on the front ange.
19. Mount the washer and the screw in the
front ange to x the swash plate.
20. Tighten the screw to a torque of 5 Nm and
remove the tool.
Guide pin
22. Mount the front ange on the housing
using the pin as guide.
23. Remove the tool.21. Mount the tool over the shaft.
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180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
Service guide | Disassembling and assembling PAH 20-25-32
25. Tighten the screws to a torque of 30 Nm
and mount the parallel key on the shaft.24. Mount the screws in the front ange.
180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
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Service guide | Disassembling and assembling PAH 20-25-32
4. Service kit list for PAH 20-25-32
Pos. Qnt. Unit Designation Material
- 1 Pcs.
- 1 Pcs.
- 1 Pcs.
1 1 Pcs.
2 2 Pcs.
3 2 Pcs.
4 2 Pcs.
31 1 Pcs.
34 2 Pcs.
61 1 Pcs.
64 1 Pcs.
65 1 Pcs.
66 9 Pcs.
67 1 Pcs.
91 1 Pcs.
92 1 Pcs.
93 9 Pcs.
94 9 Pcs.
181 1 Pcs.
182 1 Pcs.
183 1 Pcs.
184 1 Pcs.
186 6 Pcs.
187 1 Pcs.
188 1 Pcs.
211 1 Pcs.
212 1 Pcs.
215 1 Pcs. Shaft seal
218 6 Pcs. Screw
219 1 Pcs. Screw
220 1 Pcs. Usit ring
- 1 Pcs.
Shaft bush, torpedo - X
Press tool for 28 mm shaft - X
Mounting screw - X
Housing PAH AISI 304
Pin AISI 304 X
Plug AISI 304
O-ring NBR X
Swash plate Stainless steel (1.4057) X X X
Pin AISI 304 X
Cylinder barrel AISI 304 X X X
Retainer ball Stainless steel (1.4057) X X
Retainer plate Stainless steel (1.4057) X X
Piston Stainless steel (1.4057) X X
Key AISI 304 X
Port plate AISI 304 / PEEK X
Valve plate Stainless steel (1.4057) X
Back-up ring PTFE X X
O-ring NBR X X
Port ange AISI 304
O-ring NBR X
Guide pin AISI 304 X
Pin AISI 304 X
Screw AISI 304 X
Threaded plug Polymer
Threaded plug Polymer
Mounting ange AISI 304
O-ring NBR X
AISI 304/NBR X
AISI 304 X
AISI 304 X
AISI 304/NBR X
Service instruction (180R9168) X X X X X X X X X X X
180B4115 - Screw & seal kit
180B4116 - Valve plate kit
180B4119 - Piston kit
(Standard pump)
180B4117 - Piston kit
(Tech. Water pump)
180B4120 - Cylinder Barrel
(Standard pump)
180B4118 - Cylinder Barrel
(Tech. water pump)
180B4128 - Cylinder Barrel CCW
(Standard pump)
180B4494 - Swash plate kit PAH 20
180B4007 - Swash plate kit PAH 25
180B4008 - Swash plate kit PAH 32
180Z0236 - Tool set
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180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
Service guide | Disassembling and assembling PAH 20-25-32
5. Exploded view
PAH 20-25-32
180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 06.2017
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Danfoss A/S
High Pressure Pumps
Nordborgvej 81
DK-6430 Nordborg
Denmark
© Danfoss | DCS (im) | 2017.06
180R9168 | 521B1099 | DKCFN.PI.012.C3.02 | 16
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