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
			serviced in conditions of absolute cleanliness.
	10 mm combination wrench		Place the pump on a pallet or other stable
	•	13 mm combination wrench
			surface above the ground. Ensure that the pump
	•	6 mm allen key
			cannot roll. It must be possible to place the pump
	•	Adjustable pin wrench
			vertically with the shaft pointing downwards. This
	•	Stop for retainer plate
			can be done between two pallets or between
	•	Press bush for valve plate
			two boards on a pallet provided that the distance
	•	Shaft seal extractor Ø45	is minimum 50 mm.
	•	M8 allen screw (20 mm and 140 mm)	For a better understanding of the pump, please
	•	Press bush Ø45 (Plastic)
	•	M8 mm eye bolt	see the exploded view on page 19 and 21.
	•	M8 mm nut	WARNING:
	•	M8 x 70 mm screw

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.

3.Remove ceramic ring from flange 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 fit underneath the shaft seal. Press the arms of the extractor together when turning the bolt.

2.Using a 10 mm combination wrench, unscrew the four bolts from shaft seal flange.

If shaft seal flange is stuck, screw in two bolts in holes in the flange to remove it.

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 filtered 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 flange except the three shown in the next picture.

WARNING:

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

10.Screw the eye bolt in the M8 hole in the middle of the flange. 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.

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

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.

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 flange is to be changed.

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.

17. Remove the port plate by hand.

19.Place the pump horizontally. Remove the remaining screws in port flange by using a 13 mm combination

wrench. Carefully separate house and port flange. 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.

Important:

It is essential that the pump is serviced in conditions of absolute cleanliness. All parts must be absolute clean before mounting.

1.Lubrication:

•To prevent seizing-up, lubricate all threads with PTFE lubrication type.

•O-rings inside pump may be lubricated only with clean filtered water.

•O-rings for port flange, mounting flange and flushing valve must be lubricated.

•It is important to lubricate ALL parts to be assembled with clean filtered water (Especially all PEEK parts).

3.Mount O-ring.

Insert pin for positioning housing on port flange.

Ensure that two screw holes can be reached from below.

2.Place port flange with O-ring pointing upwards.

4.Position housing alingning pin hole over pin. Carefully press the port flange

downwards. Do not squeeze the O-ring. If the O-ring is damaged, the pump will leak. Screw in at least two screws.

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