Kärcher HD 1090 Service Handbook page 11

Unit function
Pressure and flow control
with the Servopress handgun
1 Threaded plug
2 Pressure holding valve
3 Spring
4 Ball
5 Valve seat
6 Connecting channel to suction chamber
7 Piston Rod
8 Threaded fitting
9 Spring
10 Pressure switch
11 Locking nut
12 Adjusting nut for pressure switch
13 Locking nut
14 Adjusting nut for operating pressure
15 High-pressure outlet
16 Control pressure injector
17 Connecting channel between injector
and overflow valve
18 Pressure chamber
19 Pressure gauge connection
1. When the Servopress handgun is
opened
When the Servopress handgun is fully opened,
water flows out of the pressure chamber (18),
through the pressure holding valve (2) and injec-
tor (16) then on to the high-pressure outlet (15).
The ball (4) in the overflow valve is pressed
against the valve seat (5) by the pump pressure
and closes off the connecting channel (6) to the
suction chamber. The pressure gauge shows
the operating pressure within the pressure cham-
ber (18). The action of the injector (16) results in
a pressure level in the connecting channel (17)
that is approx. 30 bar lower.
2. The Servopress handgun is partially
closed
When the handgun is partially closed, the pres-
sure in the pressure chamber (18) does not
increase. Due to the decreased water flow rate,
the effect of the injector action (16) is reduced, so
that the pressure in the connecting channel (17)
rises. The pistonrod (7) is pushed to the left
slightly against the spring pressure (9). The tape-
red tip of the rod pushes the ball (4) away from its
seat (5) slightly, so that a part of the pump flow rate
flows into the suction chamber (6).
Note:
Opening or closing the Servopress handgun
while the cleaner is operating in high-
pressure mode does not result in a change
to the motor current consumption. The
current consumption is only reduced when
the cleaner is being operated in cleaning
agents mode.
3. The Servopress
completely closed
As the handgun closes, the pressure in the
pressure chamber (18) rises abruptly. This peak
of pressure acts upon the pistonrod (7) via the
connecting channel (17) and forces the piston-
rod (7) all the way to the left (approx. 4 mm). The
tapered tip of the pistonrod (7) pushes the ball (4)
completely off its seat, so that the entire pump
flow rate flows through the connecting channel
(6) into the suction chamber.
As soon as the handgun is closed, the pressure
holding valve (2) closes. This trapped pressure
holds the valve in the by-pass mode.
When this position is reached, the pressure
switch (10) is actuated, the electrical supply
interrupted and the motor switched off.
4. The Servopress handgun is opened
If the handgun is opened again, the pressure in
the system drops off abruptly.
The overflow valve is pushed back towards the
right into its original position by the spring. The
pressure switch (10) reconnects the electrical
supply and the motor is switched on again.
handgun is
9