PLUG 8T8337 - Caterpillar

Pump Flow
The oil from piston pump (8) flows to the P2 port in main control valve (1). When the hoist control valve is in the LOWER position, oil flows through diverter valve (1j) into the hoist system. Oil flow out of diverter valve (1j) to the hoist system flows through check valve (1g), out of port P, and then to hoist control valve (3) .At the same time, oil flow from piston pump (9) flows to the P1 port in main control valve (1). Oil flows through diverter valve (1o) and check valve (1n). The oil then combines with the oil flow from piston pump (8) .When valve spool (3c) is in the LOWER position, Oil flow is directed to the rod side of hoist cylinders (2). At the same time, return oil flow is directed through valve spool (3c) back to the hydraulic tank. Hoist cylinders (2) retract and the dump body is lowered.Relief valve (3d) controls the maximum system pressure in order to lower the dump body.Load Sensing Flow
An Internal passage within valve spool (3c) allows oil from the oil supply to the head end of hoist cylinders (2) into the load sensing system.Load sensing pressure enters main control valve (1) at the LS port. The sensing pressure then moves shuttle valve (1a). This allows sensing pressure out of the LS2 port to piston pump (8). At the same time, the sensing pressure then moves shuttle valve (1gg). This allows sensing pressure out of the LS1 port to piston pump (9) .The load sensing pressure that is sent to piston pump (8) and (9) will cause the output of the piston pumps to increase in order to match the requirements of the hoist system. Hoist Control in the FLOAT Position
Illustration 4 g01106409
(1) Main Control Valve (1a) Shuttle Valve (1b) Orifice (1f) Pressure Reducing Valve (1g) Check Valve (1j) Diverter Valve (1k) Diverter Valve (1n) Check Valve (1o) Diverter Valve (1p) Screen (1q) Orifice (1r) Check Valve (1t) Check Valve (1u) Orifice (1v) Screen (1cc) Shuttle Valve (1gg) Shuttle Valve (2) Hoist Cylinders (3) Hoist Control Valve (3a) Pilot Control Actuator (3b) Pilot Control Actuator (3c) Valve Spool (6) Pressure Switch (8) Piston Pump (Steering and Hoist) (9) Piston Pump (Brake, Hoist and Steering)Pilot Oil Flow
When the hoist control lever is moved to the FLOAT position, a pulse width modulated signal is sent to the ECM. The ECM sends a current to pilot control actuator (3b) .Oil flow from the P1 port flows through screen (1v), orifice (1u) and check valve (1t) to pressure reducing valve (1f) .The oil flows from pressure reducing valve (1f) out of the J port to pilot control actuators (3a) and (3b) at hoist control valve (3) .When the pilot control actuator (3b) is activated, pilot oil is allowed to flow through the pilot control actuator in order to move valve spool (3c) to the FLOAT position. Pump Flow
The oil from piston pump (8) flows to the P2 port in main control