H Y D R A U L I C S Y S T E MTM 5-3805-258-24-1S Y S T E M S O P E R A T I O Ntion. The pilot oil at the left end of the lift valve spoolgoes back to lift stem (7) and on to hydraulic tank (18).The implement oil in lift cylinders (21) is held by liftvalve spool (22) and movement of the cylinder pistonsand rods stops. The lift arms and bucket are held upuntil the lift control lever is moved again.LOWER OperationWhen the lift control lever is moved to LOWERposition, lower stem (6) moves to LOWER position.There is no detent for this position. Pilot oil is nowfree to go through lift and tilt pilot valve (5) to theright end of lift valve spool (22). The lift valve spoolmoves to the left. The pilot oil at the left end of liftvalve spool (22) goes back to lift stem (7) and on tohydraulic tank (18).The movement of lift valve spool (22) stops theflow of oil through lift and tilt control valve (26).Implement pump pressure increases and opens loadcheck valve (25). The oil from the implement pumpsection (27) now goes to the rod end of lift cylinders(21) and causes the cylinder pistons and rods toretract. The lift arms cause the bucket to lower. Themovement of the cylinder pistons and rods pushes theoil out of the head end of the lift cylinders. This oilcomes into lift and tilt control valve (26) and goesaround lift valve spool (22) on its way back to oilfilters (29) and hydraulic tank (18).When the lift control lever is released, the leverand lower stem (6) go back to HOLD position. Theflow of pilot oil through lift and tilt pilot valve (5) isstopped. The springs on lift valve spool (22) move thevalve spool back to HOLD position. The pilot oil atthe right end of the lift valve spool goes back to lowerstem (6) and on to hydraulic tank (18). The imple-ment oil in lift cylinders (21) is held by lift valve spool(22) and movement of the cylinder pistons and rodsstops. The bucket is held in the lowered position untilthe lift control lever is moved again.FLOAT OperationWhen the lift control lever is moved to FLOATdetent position, lower stem (6) moves to FLOATposition. The flow of pilot oil to lift valve spool (22) isthe same as in LOWER position. The only differenceis the vent passage in lift and pilot valve (5) is openedto hydraulic tank (18) by the movement of lowerstem (6). This permits make-up valve (24) to openand lets implement oil go directly to hydraulic tank(18). The head end and rod end of lift cylinders (21)are also open to the hydraulic tank. Outside forces onthe bucket will control the movement of the cylinderpistons and rods.The lift control lever must be manually moved outof the FLOAT detent position. There is no kickoutfor the FLOAT position.LOWER Operation With Engine OffThe bucket can be lowered with the engine off. Thepilot oil supply comes from the head end of the liftcylinders. This oil goes through check valve (14) toselector and pressure control valve (10) which de-creases the pressure of the oil to approximately 1030kPa (150 psi). The oil then goes to lift and tilt pilotvalve (5). When the lift control lever is moved toLOWER and on to FLOAT detent position, lowerstem (6) moves to FLOAT position. Pilot oil goes tolift valve spool (22) and moves it to LOWER posi-tion. The head end of lift cylinders (21) is now opento hydraulic tank (18). Make-up valve (24) is ventedso it opens and the rod end of lift cylinders (21) isopen to hydraulic tank (18) also. The weight of thebucket and lift arms causes the bucket to lower to theground.NOTE: When the engine is off and the lift arms areraised, the bucket can also be dumped.ATTACHMENT (THIRD) CIRCUITCLOSE or LOWER OperationWhen the engine is running with the controllevers in HOLD position, pilot pump section (19)takes oil from hydraulic tank (18) and sends it firstto pilot section relief valve (17) which controls themaximum pressure in the pilot system. The pilotoil flow then divides. Some oil goes through line(16) to the hand metering unit of the steering system.Some oil goes through check valve (15) and selectorand pressure control valve (10) to lift and tilt pilotvalve (5). The pilot oil then goes on to attachment(third) pilot valve (33). The valve stems in the pilotvalves stop the flow of oil in HOLD position. Theoil from pilot pump section (19) goes through pilotsection relief valve (17) through oil filters (29) andback into hydraulic tank (18).At the same time, steering pump section (20)sends oil through line (23) to the steering controlvalve of the steering system. Also, implement pumpsection (27) sends oil to main relief valve (4) whichcontrols the maximum pressure in the implementoil system. The oil then goes through attachment(three spool) control valve (38) because all threevalve spools are in HOLD position. The oil thengoes through oil filters (29) and back into hydraulictank ( 18). If oil filters (29) get full of foreign material(debris), filter bypass valve (28) will open and letthe return oil go directly into the hydraulic tank.3-113
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