Unit Function HDS Middle Range / HDS Premium RangePage 58 / 127 Service Manual 04.20082.26 Pressure and flow control valve function2.26.1 Pressure and flow control valve,manually using handleThe pressure and flow control valve with thehandle (see page 104, Item 1) is used to relievethe motor during primarily part-load operation.If the spindle (3) is turned in a clockwise direction,the prestress in the spring (5) is reduced. Thisraises the overflow piston (6) even if the valveseat (14) is at a low pressure and part of the flowrate flows via the sleeve with throttle bore (12) tothe suction chamber.The pump continues to run with reduced pressure.The pressure and volume of water changesdepending on the spindle setting.2.26.2 Pressure and flow control valveusing the rotary controlThe pressure and flow control valve with rotarycontrol on the handgun should be used foroccasional part-load operation only.If the pressure is reduced via the rotary control,the manual pressure and flow control valve atthe pump must always be completely opened(„+“ direction on the handle). Otherwise the unitswitches off prematurely.If the rotary control is partly closed the pressurein the system rises. This causes the piston (6) tobe lifted from the valve seat (14), so that part ofthe flow rate flows via the return to the suctionchamber.The pump continues to run with a high pressure.The pressure and volume of water changesdepending on the rotary control setting at thehandgun.2.26.3 Handgun closedIf the handgun is now completely closed, thepiston (6) opens fully and the whole flow rate ofthe pump flows via the throttle bore (12) to thesuction chamber. The dynamic pressure, whichforms by the throttle bore of the sleeve in thereturn, activates the pressure switch (14), whichthen switches off the unit.
