RAISE Operation

TM-5-3805-258-24-1 Loader Scoop Type DED 4x4 Articulated Frame Steer 2 1/2 Cubic Yard Bucket (CCE) Airborne/Airmobile Manual
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H Y D R A U L I C S Y S T E M TM 5-3805-258-24-1 S Y S T E M S O P E R A T I O N Oil from the implement pump section goes through inlet passage (10) around tilt valve spool (11) before it goes to lift valve spool (16). The lift valve spool is a spring-centered, open center, pilot operated spool with three positions: RAISE, HOLD and LOWER. Make-up valve (19) provides the FLOAT operation of the lift circuit. Springs (18) keep lift valve spool (16) in HOLD position when there is no pilot pressure oil in chambers (17) and (27). Movement of the spool is controlled by pilot pressure oil from the lift and tilt pilot valve in chambers (17) and (27). When lift valve spool (16) is in HOLD position, implement oil goes from inlet passage (10), through passage (14) and outlet passage (15) to the hydraulic tank. The position of the spools holds (blocks) the oil in both ends of the lift cylinders and keeps the cy- linders from movement. RAISE Operation When the lift control lever is moved to RAISE posi- tion, pilot oil is sent to chamber (17) and lift valve spool (16) moves to the right. Implement oil is sent from inlet passage (10) to load check valve (25). The load check valve does not open until the oil pressure becomes greater than the force of spring (26) and the head end pressure of the lift cylinders. The oil opens load check valve (25), goes through passage (24) and out passage (23) to the head end of the lift cylinders. This causes the bucket (lift arms) to lift. Oil from the rod end of the lift cylinders comes through passage (22), goes around lift valve spool (16), through passage (13) and outlet passage (15) to the hydraulic tank. LOWER Operation When the lift control lever is moved to LOWER position, pilot oil goes to chamber (27) and lift valve spool (16) moves to the left. Oil flow to the lift cylinders is now the reverse of oil flow in RAISE position. Implement oil is sent from inlet passage (10) to load check valve (25). The load check valve opens when inlet pressure becomes greater than the force of spring (26) and the rod end pressure of the lift cylinders. The oil now goes through passage (24) and out passage (22) to the rod end of the lift cy- linders. This causes the bucket (lift arms) to lower. During this operation when the lift cylinder rods retract faster than the pump can provide oil to the rod ends, make-up valve (19) moves against spring (21) and the pressure of the oil in vent passage (20). This permits oil from the tank to add to the implement oil and prevents cavitation (vacuum) in the system. Oil from the head end of the lift cylinders comes through passage (23), goes around lift valve spool (16) and through outlet passage (15) to the hydraulic tank. FLOAT Operation When the lift control lever is moved to FLOAT position, the movement of lift valve spool (16) is the same as in LOWER position. The lift and tilt pilot valve opens vent passage (20) to a tank passage and make-up valve (19) is free to open. Implement oil pressure holds the make-up valve open. The pump oil from passage (24) and the oil in passage (22) now goes through passage (13) and outlet passage (15) to the hydraulic tank. The lift cylinders can now move freely in either direction according to the amount and direction of force on the bucket. As the cylinder rods move, all extra oil goes out passage (15) to the hy- draulic tank and pump oil comes in from inlet pas- sage (10). 3-105

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