Karcher Karcher-Pressure-Washer-Repair-Manuals/Karcher-Pressure-Washer-Parts-and-Basic-Repair-Service-Manual-Pump-785-HD2500G-HD2500MTD-HD2600DK-HD2700DH-HD2701DR Repair Manuals

Service Handbook

High-Pressure

Washer Pump

3.532-785.0

10.00

For Karcher Pressure Washer Parts Call 606-678-9623 or 606-561-4983

Pump 785 9/28/01 3:06 PM Page 1

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For Karcher Pressure Washer Parts Call 606-678-9623 or 606-561-4983

Pump 785 9/28/01 3:06 PM Page 2

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TROUBLESHOOTING OVERVIEW

Tools Necessary to Service the
KARCHER®High-Pressure Washer Pump
Part 3.532-757.0

Special Tools

•

Valve pliers . . . . . . . . . . . . . . . . . . . . . . . . . 4.901-062

•

Installation tool . . . . . . . . . . . . . . . . . . . . . . 2.901-034

(HP seal, oil seal)

•

Silicon grease . . . . . . . . . . . . . . . . . . . . . . . 6.288-044

(for packing and O-rings)

•

Lithium grease . . . . . . . . . . . . . . . . . . . . . . 6.288-079

(for O-rings on bypass valve)

•

Non-detergent pump oil . . . . . . . . . . . . . . . .6.288-050.0

Generic Tools

•

Allen Wrench 8mm

•

Allen Wrench 6mm

•

Torx TX30 Socket Wrench

•

Needle Nose Pliers

•

Rubber Mallet

•

Pliers

•

Flat Head Screwdriver

•

Phillips Head Screwdriver

•

Hammer

•

Safety Goggles

How to Use This Manual

It is not necessary to read this entire manual to find a solution
to a problem. This manual identifies four basic ways the pump may
malfunction. Find the section that defines the malfunction
of the pump. Turn to that section's overview page and identify
the specific problem. Then go to the solutions page for that
specific problem. If you don't know what the problem is, work your
way through the problems listed until you find and correct the
problem.

Low Water Pressure . . . . . . . . . . Section 1

Water Leaks . . . . . . . . . . . . . . . . . Section 2

Oil Leaks . . . . . . . . . . . . . . . . . . . Section 3

Detergent Delivery Failure . . . . . Section 4

Always wear safety rated eye protection and clothing.

For any other problems contact KARCHER

®

technical support

at 1-800-877-2424.

3

For Karcher Pressure Washer Parts Call 606-678-9623 or 606-561-4983

Pump 785 9/28/01 3:06 PM Page 3

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MASTER DIAGRAM

For Karcher Pressure Washer Parts Call 606-678-9623 or 606-561-4983

Pump 785 9/28/01 3:06 PM Page 4

5...Oil drain
plug ring

6...Oil drain

plug

1...Oil reservoir vent cap

2...Oil filter

3...Oil reservoir

4...O-ring

7...Oil bath housing

8...Pump shaft seal

9...Forward O ring

10...Swash assembly

11...Swash plate ball bearings

12...Swash

13...Piston (3)

31...Detergent check valve

32...O-ring

33...Ball bearing

34...Spring

35...Detergent tube

36...Detergent filter

17...Pressure/volume control knob

18...Bypass valve

19...Bushing

25...Low pressure check valve basket (3)

20...High pressure seal (3)

21...Pump head

22...Water outlet

23...Non-return check valve

24...Nozzle insert

26...Low pressure check valve spring (3)

27...Low pressure check valve plate (3)

28...Low pressure check valve seat (3)

29...Water inlet

30...Water inlet filter

14...Piston spring (3)

15...Weep holes (3)

16...Piston housing

39...Low pressure oil seal (3)

40...Seal retaining ring (3)

41...Bushing seal (3)

42...Bushing (3)

43...Scraper ring (3)

44...Piston guide retaining screw (2)

45...High pressure valve slide

56...Water outlet bolt (4)

37...Retainer nut

38...Thermal relief valve

46...High pressure valve seat (3)

47...High pressure valve plate (3)

48...High pressure valve spring (3)

49...High pressure valve basket (3)

50...High pressure valve cap (3)

51...Pump head bolt (4)

52...Spring

53...Ball bearing seat

54...Ball bearing

55...Safety relief valve

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KARCHER OVERVIEW

When the piston (13) is pushed forward by the swash assembly (10),
the low-pressure check valve (25-28) closes and water is conveyed
through the open high-pressure check valve (46-49) to the water
outlet (22). The pressure that is generated is dependent upon the flow
rate and the orifice diameter of the high-pressure nozzle.

Bypass Valve with Pressure Adjustment

When the trigger of the spray gun is pulled, the entire pump capacity
flows through the nozzle insert (24) to the water outlet (22). At this
time, the bypass valve (18) remains in the upper position and closes
off the path between the pressure chamber and the suction chamber.

When the trigger of the spray gun is released, water ceases to flow
through the nozzle insert (24). The non-return check valve (23) closes,
and the pressure in the high-pressure hose is maintained between the
trigger-actuated valve in the spray gun and the non-return check valve
(23). The pressure instantly rises in a surge, which causes the bypass
valve (18) to be pressed downwards. This opens the path between the
pressure chamber, located above the bypass valve (18), and the water
inlet housing (29). The pump continues to run only in bypass mode.
The safety relief valve (55) will open if the bypass valve (18) fails to
activate.

When the trigger of the spray gun is again pulled, the pressure in the
high-pressure hose drops suddenly. The spring inside the bypass valve
(18), together with the restricted pressure at the entrance to the
nozzle insert (24), pushes the bypass valve upwards. This causes the
circulation between the pressure chamber and the water inlet (29) to
close, and the pump builds up pressure once more.

This pump has a pressure/volume control (17) that enables you to
adjust the pressure and water flow at the pump. Other pumps have a
fixed pressure rating and are non adjustable. The pump shown in the
diagram is adjustable. This adjustment is made by turning the
pressure/volume control (17) downwards. This causes the bypass
valve (18) to be pushed open in a continuous movement. A part of the
pump’s capacity then flows from the pressure chamber into the water
inlet housing (29) and the operating pressure drops to the amount that
has been set by turning the pressure/volume control (17).

Thermal Protection Device

If the pump should continue to run in the bypass mode for an
extended amount of time (max 5 min.), the water circulating within the
pump will reach a temperature level that will cause internal damage.
This is prevented by the thermal relief valve (38). The thermal relief
valve will release the hot water and then automatically reset itself.

Detergent Delivery System

In this system there is a nozzle insert (24) in the water outlet (22). The
entire pump capacity flows through the nozzle insert to the spray gun.

Detergent can only be drawn in by the nozzle insert (24) if the nozzle
of the spray wand has been set to low pressure. This causes the pump
pressure to fall to approximately 435 PSI (low pressure), and the
greatest degree of negative pressure (11.6 PSI) is generated at the
lateral hole in the nozzle insert so that detergent can be drawn into
the unit via the detergent suction tube (35) and detergent filter (36).

If the spray nozzle on the spray wand is set for high-pressure
operation, the hole in the nozzle insert (24) does not create any

Swash Plate Assembly

The three pistons (13) are driven by the swash plate assembly (10),
which is mounted to the engine shaft. In the case of a vertically
configured machine, a drive bolt is screwed into the engine shaft and
then inserted into the pump shaft. As soon as the engine shaft rotates,
the swash assembly (10) rotates as well. This causes the pistons (13)
to move backwards and forwards. The piston stroke depends upon the
angle of the swash assembly (10). The greater the angle of the swash
plate, the longer the piston stroke. One revolution of the swash plate
gives the pistons one suction stroke and one pressure stroke.

Oil Bath

The swash plate assembly and pistons are bathed in oil (oil type
15W40 non-detergent). The oil level should be just above the high side
of the swash plate (12). It is important that the machine is on level
ground when checking the oil level.

In order to drain the oil, the drain plug (6), located beneath the oil bath
housing (7) will have to be removed. To add oil, remove the vent cap
(1) from the oil reservoir (3) and add to the required level.

Note: Some pumps do not have a drain plug, or oil reservoir. In order
to add oil in this case, the pump head (21) and piston housing (16) will
have to be removed.

Pistons With Seals

The three pistons (13) are pressed against the swash plate (12) of the
swash plate assembly (10) by powerful springs (14). These three
pistons are manufactured from tempered, surface-hardened steel and
are non-corrosive with regards to detergents and rust.

The pump delivery capacity is determined by

- the rotational speed of the motor

- the diameter of the pistons

- the length of the piston stroke.

The pistons (13) in industrial units are fitted with a high-pressure seal
(20) and a low-pressure seal (39). Non-industrial units have only a
high-pressure seal (20).

The three pistons each have an oil seal (39) mounted in the piston
housing (16). These three oil seals, along with the shaft seal (8), retain
the oil in the oil bath housing. The weep holes (15) are in the piston
housing (16) and allow water or oil to drip out into the open.

A water leakage rate of one drop per piston per minute is allowable
during high-pressure operation. If oil is leaking from the weep holes
(15), there is either a leak in the oil seals or there is piston damage.

Low-Pressure and
High-Pressure Check Valves

Each piston works with one low-pressure check valve (25-28) and one
high-pressure check valve (46-49). Each of these check valves is
constructed of the same basic components: the valve cage, spring,
valve plate with guide shaft and the valve seat with O-ring.

The sealing surface between the valve plate (27 & 47) and the valve
seat (28 & 46) is conical. The valve plate and valve seat are
manufactured from either plastic or stainless steel depending upon the
particular unit involved.

When the piston (13) is forced backwards by the spring (14) in the oil
bath housing (7), the high-pressure check valve (46-49) closes and
water is drawn in through the supply line / suction chamber at the
water inlet (29), through the inlet filter (30), and through the open low­pressure check valve (25-28).

5

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Pump 785 9/28/01 3:06 PM Page 5

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negative pressure, and no detergent can be drawn into the unit.

The detergent check valve consists of a small spring (31) with a ball,
O-ring and nipple. When operating in the detergent mode, the negative
pressure created by the nozzle insert causes the ball to be drawn

away from the O-ring, against the tension of the spring. Detergent can
then be drawn into the unit.

When operating in the high-pressure mode, the ball seals off the
detergent connection so that no water can flow into the container of
detergent.

6

KARCHER OVERVIEW

PART NUMBERS

High Pressure Washer Pump 3.532-785.0

ITEM #(S)

DESCRIPTION PART # QTY. IN

PUMP

1 Oil reservoir cap 5.063-651.0 1
2 Oil filter 5.132-107.0 1
3 Oil reservoir 5.070-194.0 1
4 O-ring 6.362-168.0 1
5 Oil drain plug ring 7.362-003.0 1
6 Oil drain plug 7.382-085.0 1
7 Oil bath housing 5.093-207.0 1
8 Pump shaft seal 7.387-018.0 1
9 Forward o-ring 6.363-067.0 1

10 Swash plate assembly with 5.120-326.0 1

Cylinder bearing 7.401-027.0 1

Coupling element 4.120-192.0 1

Spring 7.318-002.0 1
11 Swash plate ball bearings 6.401-185.0 1
12 Swash plate 5.120-326.0 1
13 Piston 5.553-434.0 3
14 Piston spring 6.332-427.0 3
15 Piston housing 5.060-677.0 1
16 Pressure/volume control knob with 5.321-307.0 1

Spindle 4.401-079.0

17 Bypass valve (multiple numbers)

top o-ring set 6.362-454.0 1

piston 5.553-383.0 1

spring 5.332-425.0 1

valve seat 5.581-242.0 1
valve seat o-ring 6.362-169.0 1
threaded spindle 5.305-274.0 1

18 Bushing 5.110-630.0 1
19 High-pressure seal 6.365-432.0 3
20 Pump head 5.550-266.0 1
21 Water outlet 5.063-897.0 1
22 Non-return check valve 5.584-091.0 1
23 Nozzle insert 5.769-138.0 1

24, 25 Low-pressure check valve basket, 4.580-371.0 3
26, 27 spring, plate and seat

ITEM #(S)

DESCRIPTION PART # QTY. IN

PUMP

28 Water inlet housing 5.063-897.0 1
29 Water inlet filter 6.414-252.0 1
30 Detergent check valve 5.443-448.0 1
31 O-ring 6.362-175.0 1
32 Ball-bearing 7.401-909.0 1
33 Spring 5.332-258.0 1
34 Detergent tube 6.388-216.0 1
35 Detergent filter 4.862-032.0 1
36 Retainer nut 5.411-150.0 1
37 Thermal relief valve 5.413-067.0 1
38 Low pressure oil seal 6.365-340.0 3
39 Seal retaining ring 5.115-465.0 3
40 Bushing seal 6.365-434.0 3
41 Bushing 5.112-576.0 3
42 Scraper ring 5.115-744.0 3
43 Piston guide retaining screw 7.303-047.0 2
44 High pressure valve slide 5.003-983.0 1

45,46 High-pressure valve cage, spring, 4.580-371.0 3
47,48 plate and seat

50 Pump head bolts 7.306-047.0 4
51 Spring 5.332-446.0 1
52 Ball-bearing seat 5.411-070.0 1
53 Ball-bearing 7.401-909.0 1
54 Safety relief valve 5.583-164.0 1
55 Water outlet bolt 7.306-105.0 4

NOT PICTURED IN DIAGRAM

Garden hose connection 9.154-009.0 1
Piston spring retaining clip 7.343-478.0 3

For Karcher Pressure Washer Parts Call 606-678-9623 or 606-561-4983

Pump 785 9/28/01 3:06 PM Page 6

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