Karcher HD 9-18-4 ST: Function

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1 Solenoid valve water supply (upgrade 

kit, optional)

2 Water inlet

3 Swimmer valve

4 Container of softener liquid

with solenoid valve (4.1), only with mod-

el ST-H (option with model ST)

5 Prepressure pump, only with model ST-

H

6 High pressure pump

7 Overflow valve

8 Back up valve

9 Pressure switch

10 Detergent injector

11 Pressure relief valve (upgrade kit, op-

tion)

12 Vibration dampener

13 High-pressure outlet

14 Pipe system (option)

15 High pressure hose

16 Trigger gun

with shutoff valve (16.1) and pressure/

volume regulation (16.2)

17 High pressure nozzle (triple nozzle)

18 Backflow valve, detergent suction un-

der low pressure

19 Dosage valve for detergent

20 Level sensor detergent (upgrade kit, 

optional)

consisting of 1 detergent solenoid valve 

(20.1) and 1 detergent level sensor 

(20.2).

21 Cleaning agent container

22 Detergent dosing 2nd detergent, (up-

grade kit, option), consisting of 1 deter-

gent dispensing valve (22.1), 1 deter-

gent solenoid valve (22.2), 1 detergent 

level sensor (22.3)

23 Detergent dosing 2nd detergent under 

high pressure (upgrade kit, option), 

consisting of 1 detergent pump (23.1), 

and 1 detergent level sensor (23.2)

24 Detergent dosing, double under high 

pressure (upgrade kit, option), consist-

ing of 1 detergent dispensing valve 

(24.1), 2 detergent pumps (24.2), and 2 

detergent level sensor (24.3)

25 Water filter (option)

With the decrease in total water flow the 

water runs through the water inlet, the 

swimmer tank, advance pressure pump hot 

water and through the high-pressure pump 

to the high-pressure outlet.  

If only a part of the water capacity fed from 

the pump is needed, the rest of the flow 

runs through the flow regulator back to the 

suction site of the high-pressure pump.

Detergent is suctioned via the detergent in-

jector and metered using the detergent dis-

pensing valve.

In order activate the suction, the multi-noz-

zle must be set to "CHEM" (low pressure 

flat jet).

With the upgrade kit "Detergent dosing in 

high pressure mode (option)", detergent 

can be added via a detergent pump.

If the system pressure sinks during the 

standby period due to the opening of one of 

the consumers, the pressure switch will 

switch on the high pressure pump.

Adding liquid softener will prevent the build-

up of lime when operating with hot water. 

Starting with a hardness range of "medium" 

(8.4 - 14 °dH) and a supply temperature of 

more than 6C, the upgrade kit for water sof-

tening (DGT) must be installed, or an exter-

nal water softening system must be pre-

sent. ST-H appliances are suitable for hot 

water operation of up to 85°C; ST applianc-

es are suitable for supply water tempera-

tures of up to 70°C.

Function

Flow pattern

Full pump capacity

Parts removal

Detergent

Automatic pump start

Softener system

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EN