Specifications

Service Training
Page 4.2
Section 28
09.04
4.2.2.6 FLUSHING OF THE CIRCUIT AND HOUSING
In order to prevent extremely high oil temperatures in the closed circuit, the drive is provided with circuit
flushing through an output control device. The temperature in the hydraulic units and the tank is also
approximated by flushing the pump and the motor housing.
CIRCUIT FLUSHING
Each hydraulic motor has an output control device consisting of valve (50), nozzle (50a) and valve (51).
If high pressure exists at P, valve (51) shifts to position (a). The low pressure at S goes through the open
valve (51) and the nozzle (50a) to the pressure-relief valve (50) set to 13 bar and to the opening valve into
the motor housing. A differential pressure of 7.5 bar exists between valve (50) and low pressure. Due the
size of the nozzle (50a), the quantity of oil emitted is fixed to 3 litres per hydraulic motor. The quantity of
oil leaving at the low pressure side is replaced by cool oil flowing in through the feed valves. This method,
together with the leakage caused by the high pressure, allows the entire circulating oil to be replaced several
times per minute.
HOUSING FLUSHING
The cool oil delivered by pump G goes through filter O and travel control unit P to the feed valves (25). The
appropriate feed valve returns the same quantity of oil into the circuit as is lost due to leakage and removed
as output oil. The remaining quantity is blown off through the feed pressure valve (26) into the pump
housing, from where it flows back to the tank via port I.
The oil quantity removed from the closed circuit through the output device goes into the related motor
housing and from there to the tank, together with the leakage oil.