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the main pump. It has following advantages: long service life, low noise level, wide
range of controls, high power/weight ratio. The flow of two Pumps will converge in
the control valve first and there is divided by the driver’s intention into two parts, one
being sent to lift cylinder, tilt cylinder or extension cylinder, and another to the power
steering unit in variable flow rate to operate the steering cylinder.
Fig.8-1 Main Pump
8.3 Control Valve
(1) The work principle and structures of Control Valve
The work device of the Hydraulic System adopts the liquid to regulate the
Control Valve. here is a Relief Valve in every valve’s inlet. So it is sure that flow of
every valve is only related with orifice of the valve. In other words, its flow is
irrelevant with loading pressure. If the Pump can’t provide enough flow to keep on the
serval services working at the same time, the speed of the work services reduces with
same proportion. And it is not influence to work for the running parts.
When the Main Valve spool is placed in neutral position, maintaining valve and
pressure compensated valve will be closed. The oil from the pump outlet can’t flow
into the main valve spool so as to the work services can’t operate.
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