Caterpillar 311D 312D 314D Hydraulic Excavators Global Service Learning Manual – PDF DOWNLOAD

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SERV1851 02/08

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Text Reference Swing System

SWING PRIORITY VALVE NO PRIORITY OVER STICK

Pilot Valve

Spool

Parallel Feeder Passage

To Stick 1 Control Valve

148

When the swing joystick is partially shifted, the pilot pressure oil from the swing pilot valve cannot overcome the swing priority valve spring to move the the valve spool left. The swing priority valve spool does not restrict oil to the stick 1 control valve as shown in this illustration. Unrestricted flow from the idler pump is available to the stick 1 control valve to operate the stick. When the swing pilot valve is fully shifted, pilot oil pressure moves the swing priority valve spool to the right against spring force. With the swing priority valve spool moves to the left, supply oil to the stick 1 control valve is restricted and the stick cylinder speed is reduced.


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