ADAPTER-SPEED 1903769 - Caterpillar

Hoist Control Valve
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Hoist Control Valve in the HOLD position (3) Hoist Control Valve (3a) Pilot Control Actuator (3b) Pilot Control Actuator (3c) Valve Spool (3d) Relief Valve (3e) Check Valve (3f) Spring (3g) Spring (A) Raise Port (B) Load Sensing Port (C) Lower Port (D) Tank Port (E) Pump Port
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The hoist control valve is located on the left side rear of the tractor. (3) Hoist Control Valve (3a) Pilot Control Actuator (3b) Pilot Control Actuator (3d) Relief Valve (3e) Check Valve (A) Raise Port (B) Load Sensing Port (C) Lower Port (D) Tank Port (E) Pump PortThe position of valve spool (3c) is determined by the magnitude of the pilot pressure within pilot control actuators (3a) and (3b). This pilot pressure, that acts on the Valve spool, is controlled by the solenoids that are part of the pilot control actuators. The solenoids are connected to the hoist control, which is in the cab, via the ECM. The valve spool has four positions.HOLD position
When the engine is shut off or the engine is running, the magnitude of the pilot pressure within pilot control actuators (3a) and (3b) is zero. The valve spool is centered to the HOLD position by springs (3f) and (3g). Oil flow from the piston pumps is blocked at pump port (E) . Since there is no load sensing pressure through load sensing port (B) and no demand on the hoist system the piston pump will be at the minimum swashplate angle but the piston pumps will maintain a standby pressure.RAISE position
When the hoist control is moved to the RAISE, the ECM sends a current to pilot control actuator (3a), which is proportional to the displacement of the hoist control in the cab. Pilot control actuator (3a) is energized. The pilot pressure within the pilot control actuator moves valve spool (3c) to the RAISE position. Oil within pilot actuator (3b) is directed to the hydraulic tank. The valve spool is moved fully to the right. Oil flows from pump port