TM 5-3805-258-24-1H Y D R A U L I C S Y S T E MS Y S T E M S O P E R A T I O NWhen the attachment (third) control lever ismoved to CLOSE or LOWER position, close orlower stem (36) moves to CLOSE or LOWERposition. Pilot oil is now free to go through attach-ment pilot valve (33) to the right end of attachmentvalve spool (31). This causes the valve spool tomove to the left. The pilot oil at the left end ofattachment valve spool (31) goes through shuttlevalve (40), back to attachment pilot valve (33),through open or raise stem (37) and onto hydraulictank (18).The movement of attachment valve spool (31)stops the flow of oil through attachment controlvalve (38). Implement pump pressure increases andopens load check valve (32). The oil from implementpump section (27) now goes to the head end ofattachment cylinders (30) and causes the cylinderpistons and rods to extend. The movement of thecylinder pistons and rods pushes the oil out of therod end of the attachment cylinders. This oil comesinto attachment control valve (38) and goes aroundall three valve spools (31), (13) and (22) on its wayback to oil filters (29) and hydraulic tank (18).When the pressure of the oil to the head end ofthe attachment cylinders gets to approximately15500 kPa (2250 psi), the spool of sequence valve(39) moves up. This causes oil from close or lowerstem (36) to go through sequence valve (39) andshuttle valve (40) to the left end of attachmentvalve spool (31). The springs on the attachmentvalve spool cause it to move to HOLD position.Implement pressure oil to the attachment cylin-ders is now stopped.When the pressure of the oil to the head end ofthe attachment cylinders gets below approximately12400 kPa ( 1800 psi), the spool of sequence valve(39) moves down. This stops the flow of pilot oilto the left end of attachment valve spool (31). Thevalve spool again moves to the left (CLOSE orLOWER position) and implement pressure oilgoes to the attachment cylinders.See FO-5, STANDARD HYDRAULIC SYSTEM IN LOWER POSITION(ENGINE OFF), located in the back of this manual.The operation of sequence valve (39) and shuttlevalve (40) permits the operation of the lift and tiltcircuits during CLOSE or LOWER operation.There are no detents on the attachment control.When the attachment control lever is released, thelever, close or lower stem (36) and attachment valvespool (31) go back to HOLD position. The cylinderpistons and rods are stopped and will stay in thisposition until the attachment control lever is movedagain.OPEN or RAISE PositionWhen the attachment control lever is moved toOPEN or RAISE position, open or raise stem (37)moves to OPEN or RAISE position. Pilot oil is nowfree to go through attachment pilot valve (33) andshuttle valve (40) to the left end of attachment valvespool (31). This causes the valve spool to move to theright. The pilot oil at the right end of attachmentvalve spool (31) goes back to attachment pilot valve(33), through close or lower stem (36) and on tohydraulic tank (18).The movement of attachment valve spool (31)stops the flow of oil through attachment controlvalve (38). Implement pump pressure increases andopens load check valve (32). The oil from implementpump section (27) now goes to the rod end ofattachment cylinders (30) and causes the cylinderpistons and rods to retract. The movement of thecylinder pistons and rods pushes the oil out of thehead end of the attachment cylinders. This oil comesinto attachment control valve (38) and goes aroundall three valve spools on its way back to oil filters(29) and hydraulic tank (18).When the attachment control lever is released,the lever, open or raise stem (37) and attachmentvalve spool (31) go back to HOLD position. Move-ment of the cylinder pistons and rods is stoppeduntil the attachment control valve is moved again.See FO-7, OPTIONAL HYDRAULIC SYSTEM IN CLOSE OR LOWER POSITION, located in the back of this manual.3-114
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