W345B Series II Material Handler Hydraulic System Control Valve (Boom Lowering) Caterpillar


Control Valve (Boom Lowering)
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W345B Series II Material Handler Hydraulic System [RENR5574]
HYDRAULIC SYSTEM
VALVE GP-LOAD CONTROL
W345B Series II Material Handler Hydraulic System Control Valve (Stick Lowering)
W345B Series II Material Handler Hydraulic System Control Valve (Boom Lowering)
1.1. Construction
2.1. BOOM RAISE Operation
3.1. BOOM LOWER Operation
4.1. Boom Hold
5.1. Relief Operation of the Cylinder Head End



Illustration 1g00815213

Location of boom lowering control valve

(1) Boom lowering control valve

(2) Pump oil line

(3) Boom cylinder

(4) Return oil line

The boom lowering control valves are located on the head end of the boom cylinders.

The boom lowering control valve has two functions:

  • The boom lowering control valve prevents the boom from falling if a hydraulic supply line fails or if a supply tube to a boom cylinder fails.

  • The boom lowering control valve allows the operator to manually lower the boom when the engine is shut down.

Reference: For information on lowering the boom manually, see Operation and Maintenance Manual, "Equipment Lowering with Engine Stopped".

Construction




Illustration 2g00816555

Components of the boom lowering control valve (side view)

(1) Inlet port (A)

(2) Spool

(3) Pilot oil passage from relief valve

(4) Check valve

(5) Outlet port (C) to head end of boom cylinder




Illustration 3g00813294

Simplified hydraulic schematic (boom lowering control valve)

(1) Line from pilot valve

(2) Boom I control valve

(3) Pump line

(4) Manifold

(5) Boom lowering control valve

(6) Check valve

(7) Relief valve

(8) Spool

(9) Boom cylinder

(10) Outlet port to boom cylinder head end

(11) Drain line

BOOM RAISE Operation




Illustration 4g00817758

Boom lowering control valve

(3) Pump line

(6) Check valve

(10) Outlet port to boom cylinder head end

When the operator moves the joystick to the BOOM RAISE position, pilot oil flows through line (1) and into boom I control valve (2). The pilot oil shifts the spool that is inside the control valve. This allows pump oil to flow through line (3) into manifold (4) and into boom lowering control valves (5). The pump oil flows through check valve (6), through port (10), and into the head end of boom cylinders (9). The rod is extended and the boom raises.

BOOM LOWER Operation




Illustration 5g00820233

Boom lowering control valve

(1) Pilot line

(3) Line to hydraulic tank

(8) Spool

(10) Outlet port

When the operator moves the joystick to the BOOM LOWER position, pilot oil flows from the pilot control valve to the boom lowering control valve. The pilot pressure moves spool (8) to the left. This allows pump oil to flow through port (10) and back to the hydraulic tank through pump line (3) and boom I control valve (2) to the hydraulic tank. The cylinder rod retracts, and the boom lowers.

Boom Hold




Illustration 6g00822126

Boom lowering control valve

(6) Check valve

(8) Spool

When the operator moves the joystick to the NEUTRAL position, the boom cylinders are held in the raised position. Check valve (6) and spool (7) remain in positions that prevent hydraulic oil from flowing back through boom lowering control valve (5).

Relief Operation of the Cylinder Head End




Illustration 7g00822002

Boom lowering control valve

(6) Check valve

(7) Relief valve

(8) Spool

(10) Outlet port

When the boom is pushed downward by an outside force, the oil pressure within boom lowering control valve (5) increases. The oil pressure is sensed at relief valve (7). Oil from the cylinder head end cannot flow back through check valve (6). When the oil pressure overcomes the relief valve setting, the oil flows through relief valve (7) to spool (8). The oil pressure shifts spool (8) sideways. This allows oil to flow from port (10) through spool (8). Oil then flows back through boom lowering control valve (5) to the hydraulic tank. This action lowers the hydraulic oil pressure until the oil pressure is lower than the relief valve setting.

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