Unit Function
HDS Middle Range / HDS Premium Range
Page 58 / 127
Service Manual 04.2008
2.26 Pressure and flow control valve function
2.26.1 Pressure and flow control valve,
manually using handle
The pressure and flow control valve with the
handle (see page 104, Item 1) is used to relieve
the motor during primarily part-load operation.
If the spindle (3) is turned in a clockwise direction,
the prestress in the spring (5) is reduced. This
raises the overflow piston (6) even if the valve
seat (14) is at a low pressure and part of the flow
rate flows via the sleeve with throttle bore (12) to
the suction chamber.
The pump continues to run with reduced pressure.
The pressure and volume of water changes
depending on the spindle setting.
2.26.2 Pressure and flow control valve
using the rotary control
The pressure and flow control valve with rotary
control on the handgun should be used for
occasional part-load operation only.
If the pressure is reduced via the rotary control,
the manual pressure and flow control valve at
the pump must always be completely opened
(„+“ direction on the handle). Otherwise the unit
switches off prematurely.
If the rotary control is partly closed the pressure
in the system rises. This causes the piston (6) to
be lifted from the valve seat (14), so that part of
the flow rate flows via the return to the suction
chamber.
The pump continues to run with a high pressure.
The pressure and volume of water changes
depending on the rotary control setting at the
handgun.
2.26.3 Handgun closed
If the handgun is now completely closed, the
piston (6) opens fully and the whole flow rate of
the pump flows via the throttle bore (12) to the
suction chamber. The dynamic pressure, which
forms by the throttle bore of the sleeve in the
return, activates the pressure switch (14), which
then switches off the unit.