Citytrac 4200
Citymaster 1200
Citycleaner
Service Documents
For internal use only
Status
March 2009
Page
36 of 108
5.2.4 Hydraulic pump description
The swash plate variable displacement pump feeds 0 – 110 l/min, continually adjustable, in both directions. When at high pressure,
both outlets are set to 322 bar (Pos. 2 + 3)(pressure relief valve).
The integrated feed pump supplies a maximum of 30 l/min to compensate for oil leakage, to change a defined quantity of oil for cooling
and for diverse control functions.
The feed pump draws oil from the tank via the suction return flow filter (Pos. 204) and feeds it to the non-return valves which are
integrated in the pressure relive valves (Pos. 2 + 3). The maximum feed pressure is limited to 22 bar by the feed pressure valve
(Pos.1). The non-return valve to which high pressure is not applied enables feed to the variable displacement pump circuit.
At the same time, the feed pressure is generated via the starting cartridge for the mechanical-hydraulic control units.
Depending on the DA - regulating valve (pos.5), actuating the accelerator pedal causes the feed pressure to be supplied to the set
piston which moves the hydraulic pump's pivoting disk in the required direction and angle (feed volume/driving speed).
If the pressure at the hydraulic motors meets with resistance (gradient/obstruction) which causes a pressure increase in excess of
290bar, the overpressure is relieved, by the pressure cut-off valve, to the tank. Cause of this, the pressure will be hold at 290bar. The
function of the pressure cut-off valve is to limit the power of the pump (feed volume x pressure) to the maximum allowed value. The
pressure relief valves (Pos. 2 + 3) are used for safety reasons. Normally they are never activ.
The set feed pressure is measured at measuring points G.
The set cut-off pressure is measured at measuring points MA and MB when the wheels are blocked.
To measure the relive valve pressure, the cut-off valve has to be set to a value over 325bar. Then the relive pressure can be
measured at the points MA and MB.
After this the pressure cut-off valve must be set back to 290bar!
The correct feed pressure is a basic condition for generating high pressure.
