Danfoss PAHT 256, PAHT 308, PAHT G 256, PAHT G 308 Service guide

Service guide

PAHT / PAHT G pumps

PAHT 256-308 / PAHT G 256-308
Disassembling and assembling

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Service guide | Disassembling and assembling PAHT and PAHT G 256-308

Table of Contents 1. Introduction .............................................................................................................................................................. 2

2. Disassembling the pump ..................................................................................................................................... 3

3. Assembling the pump .......................................................................................................................................... 6

4. Disassembling and assembling of the swash plate ..................................................................................10

5. Disassembling and assembling of cylinder barrel and valve plate .....................................................11

6. Changing pistons ..................................................................................................................................................12

6.2. Assembling ..............................................................................................................................................................15

7. When should the pistons be replaced ...........................................................................................................17

8. Spare parts list for PAHT 256-308 .................................................................................................................... 18

8.1 Exploded view PAHT 256-308 ........................................................................................................................... 19

9. Spare parts list for PAHT G 256-308 ................................................................................................................20

9.1 Exploded view PAHT G 256-308 .......................................................................................................................21

1. Introduction

This document covers the instructions for disassembling and assembling the axial piston pumps
PAHT and PAHT G 256-308.

Important: It is essential that the pump is

Tools provided with toolset 180B4259
10 mm combination wrench

• 13 mm combination wrench

• 6 mm allen key

• Adjustable pin wrench

• Stop for retainer plate

• Press bush for valve plate

• Shaft seal extractor Ø45

serviced in conditions of absolute cleanliness.

Place the pump on a pallet or other stable
surface above the ground. Ensure that the pump
cannot roll. It must be possible to place the pump
vertically with the shaft pointing downwards. This
can be done between two pallets or between
two boards on a pallet provided that the distance
is minimum 50 mm.

• M8 allen screw (20 mm and 140 mm)

• Press bush Ø45 (Plastic)

• M8 mm eye bolt

• M8 mm nut

• M8 x 70 mm screw

For a better understanding of the pump, please
see the exploded view on page 19 and 21.

WARNING:
Do not reuse disassembled O-rings or shaft
seal as they might be damaged. Always use
new O-rings.

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Service guide | Disassembling and assembling PAHT and PAHT G 256-308

2. Disassembling the
pump

1. Disconnect the pump from the rest of the
system.

2. Using a 10 mm combination wrench,
unscrew the four bolts from shaft seal
ange.
If shaft seal ange is stuck, screw in two
bolts in holes in the ange to remove it.

3. Remove ceramic ring from ange by
gently pushing it from the back of the
sealing ring.

6. Carefully remove the shaft seal assembly
using the shaft seal extractor supplied in
the toolset. The extractor must t
underneath the shaft seal. Press the arms
of the extractor together when turning the
bolt.

4. Mount the M8 allen screw from the tool
set in the top of the shaft.

5. Wet the shaft and shaft seal with clean
ltered water.

7. Turn pump into vertical position with shaft

pointing downwards.

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Service guide | Disassembling and assembling PAHT and PAHT G 256-308

8. Using a 13 mm combination wrench,
remove all the bolts on the mounting
ange except the three shown in the next
picture.

WARNING:

Do not loosen the two screws keeping
swash plate in place.

9. Unscrew the remaining three bolts. Turn
each bolt one round at the time to make
sure that the ange is removed as straight
forward as possible.

10. Screw the eye bolt in the M8 hole in the
middle of the ange. Pull it straight
upwards.

12. Remove by hand the pistons one by one.
Be careful not to scratch the pistons. Tilt
the retainer plate to horizontal position for
easy removal of pistons, if required.

WARNING:

Do not use any tools.

11. Swash plate must be placed so that its
surface is not scratched. For further
disassembling of swash plate, see page 10.

13. Remove the retainer plate and the retainer
ball.

Note: As the retainer ball is not attached

to the retainer plate, it might fall out.

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Service guide | Disassembling and assembling PAHT and PAHT G 256-308

14. Remove the retainer guide, the 4 springs
and the spring guide.

15. Mount a 8 mm eye bolt in the cylinder

barrel. Pull straight upwards. A continuous
lift will elevate the cylinder barrel out of
housing. This can only be done if shaft seal
is removed.

WARNING:

If the cylinder barrel is dropped or
lowered too fast into housing, the main
bearing/shaft bearing might be
damaged. It is not replaceable.

16. Place cylinder barrel upside down.
For further disassembling of cylinder
barrel and valve plate see page 11.

18. Remove, by hand, the two pins.
Note: The following operation is only

necessary if O-ring on port ange is to
be changed.

17. Remove the port plate by hand.

19. Place the pump horizontally.

Remove the remaining screws in port
ange by using a 13 mm combination
wrench. Carefully separate house and port
ange. Ensure that pin for the positioning
house is not lost.

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Service guide | Disassembling and assembling PAHT and PAHT G 256-308

3. Assembling the pump
WARNING:

Do not use silicone when assembling the
pump. Do not reuse disassembled O-rings;
they might be damaged. Always use new
O-rings.

Note:
Place the pump on a pallet or other stable
surface above the ground. Ensure that
the pump cannot roll. It must be possible
to place the pump vertically with the
shaft pointing downwards. This can be
done between two pallets or between
two boards on a pallet provided that the
distance is minimum 50 mm.

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. Place port ange with O-ring pointing
upwards.

3. Mount O-ring.

Insert pin for positioning housing
on port ange.
Ensure that two screw holes can be
reached from below.

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4. Position housing alingning pin hole
over pin. Carefully press the port ange
downwards. Do not squeeze the O-ring. If
the O-ring is damaged, the pump will leak.
Screw in at least two screws.