PIN 1V8355 - Caterpillar

Illustration 1 g02983179The selector and pressure control valve is on the left side of the rear frame beside the transmission.The selector and pressure control valve reduces high-pressure oil from the lift cylinders. This oil is used in the pilot system when the engine is stopped and when the bucket is raised. The selector and pressure control valve routes the oil to the pilot control valve via the implement and steering solenoid valve. A raised bucket can now be lowered when the engine is stopped.When engine is running and there is a loss of pilot oil from the pilot and braking pump, the following will occur: The selector and pressure control valve will allow oil from the steering system into the pilot system at a reduced pressure.
Illustration 2 g06022044
Selector and pressure control valve
(1) Return passage to the hydraulic tank
(2) Spacers
(3) Spring
(4) Valve spool
(5) Holes (two)
(6) Passage
(7) PassageDuring normal operation, pressure oil from the pilot and braking pump is controlled by the pilot relief valve. Pressure oil from the pilot relief valve enters through passage (7). Pressure oil from the pilot relief valve also flows to the pilot control valve via the implement and steering solenoid valve.The oil is blocked at the pilot control valve causing the pilot pump oil pressure to increase. The higher oil pressure moves valve spool (4) up against spring (3). Moving valve spool (4) up covers holes (5). Oil in lift cylinder passage (6) is blocked by valve spool (4) and cannot enter the pilot system.When the lift arms are in the RAISED position and the engine is stopped, no pilot and braking pump oil is sent to passage (7). Spring (3) moves valve spool (4) down. High-pressure oil from the head end of the lift cylinders at passage (6) flows through holes (5) in valve spool (4). The oil in the center of valve spool (4) flows through passage (7) to the pilot control valve via the implement and steering solenoid valve.When the pressure through passage (7) gets too high, the pressure will cause valve spool (4) to move against the force of spring (3). The flow of oil decreases through holes (5) in the valve spool and decreases the pressure in passage (7).When the pilot control valve is moved to the LOWER position, pilot oil is sent to move the lift control spool. The lift control spool directs the oil in the lift cylinder back to the hydraulic tank allowing the bucket to be lowered.When the pilot control valve is moved to the DUMP position, pilot oil is sent to move the tilt control spool. The tilt control spool directs the oil in the tilt cylinder back to the hydraulic tank allowing the bucket to be dumped.A check valve in the line from the pilot relief valve stops oil pressure from passage (7) returning to the pilot and braking pump.