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 Boom, Stick, and Bucket Circuits

BOOM LOWERING CONTROL VALVE HOLD

Piston Boom Cylinder

Boom Control Valve Relief Valve

Spool 1

Spool 2

126

Boom Lowering Control Valves The boom circuit is equipped with boom lowering control valves (or load control valves), which are attached directly to each of the boom cylinders. The boom lowering control valves contain the following major components: - boom head end line relief - boom lowering control valve spool - orifice - manual lower - piston When the joystick is in the HOLD position, the boom cylinders are held in the raised position. Spring force moves spool 1 up and oil is trapped between the head end of the boom cylinders and spool 1. The boom lowering control valve keeps the boom cylinder from drifting down.


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