CYLINDER GP-BUCKET 3154455 - Caterpillar

Illustration 1 g03371107
Boom lowering control valve (1) Boom lowering control valve (2) Boom cylinderBoom lowering control valve (1) is located on the head end of boom cylinder (2) .Boom lowering control valve (1) has two functions:
Prevents the boom from falling if a hydraulic supply line fails or if a supply tube to boom cylinder (2) fails.
Allows the operator to manually lower the boom when the engine is shut down.ReferenceFor information on lowering the boom manually, see Operation and Maintenance Manual, "Equipment Lowering with Engine Stopped".
Illustration 2 g03371108
Simplified hydraulic schematic (boom lowering control valve) (1) Boom lowering control valve (2) Boom cylinder (3) Main control valve (4) JoystickOperations for Boom Lowering Control Valve
Illustration 3 g03371112
(1) Boom lowering control valve (2) Boom cylinder (3) Main control valve (4) Joystick (5) Inlet port (6) Sealing face (7) Outlet port to head end of boom cylinder (8) Spool 1 (9) Chamber (10) Passage to drain (11) Piston (12) Inlet port for pilot oil (13) Chamber (14) Spool 2 (15) Relief valve (16) ChamberBOOM RAISE Operation
When joystick (4) is moved to the BOOM RAISE position, the pump oil flows from main control valve (3) to boom lowering control valves (1) . The pump oil flows through port (5) . Pilot oil will move spool (8) downward. Pump oil then flows through the passage to outlet port (7) and to the head end of boom cylinder (2) . Pump oil causes the boom to raise.BOOM LOWER Operation
When joystick (4) is moved to the BOOM LOWER position, pilot oil flows from joystick (4) to port (12) . The pilot oil will move piston (11) downward. When piston (11) moves downward, hydraulic oil from chamber (9) flows through passage (10) . The downward movement opens spool (8) . Hydraulic oil then flows from port (7) to port (5) and back to the tank. Pump oil allows the boom to lower.Boom Hold
When joystick (4) is moved to the NEUTRAL position, boom cylinder (2) is held in the raised position. Spool (8) will move upward due to spring force in chamber (9) . Spool (8) will then seal against sealing face (6) . Spool (8) prevents oil from leaking from port (7) to port (5) .Relief Operation of the Cylinder Head End
When the boom is pushed downward by an outside force, the oil pressure in port (7) increases. The oil pressure is sensed at relief valve (15) . When oil pressure overcomes the relief valve setting, relief valve (15) allows oil to fill chamber (16) . The oil pressure in chamber (16) moves spool (14) downward. Oil then flows from chamber (9) to passage (10) . Pilot oil will allow spool (8) to open. Hydraulic oil will then flow from port (7) to port (5) and back to the tank. Opening of port (7) will lower the hydraulic oil pressure until the hydraulic oil pressure is lower than the relief valve setting.