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 NLIFT ANDTILT CONTROL VALVE(Lift ValveSpool in LOWER and FLOAT; Tilt Valve Spool in HOLD; Make-up ValveVented)10. Inletpassage for16. Lift valvespool.implement oil.17. Chamber for pilot oil.11. Tilt valvespool.16, Springs.13. Passage.19. Make-up valve for rod14. Passage.end of lift cylinders.15. Outlet passage to20. Vent passage to lift andhydraulic tank.tilt pilot valve.Load Check ValvesLoad check valves (9) and (25) prevent reverse oilflow in the cylinders (tilt and lift), which can causecylinder drift. For example, when the tilt valve spoolis in TILT BACK position, pump oil opens loadcheck valve (9) and goes through passages (6) and(7) to the head end of the tilt cylinder. If the pressureat inlet passage (10) decreases, the pressure of theoil, along with spring (8) will close load check valve(9) and hold the oil in the head end of the tilt cy-linder, This prevents any movement of the tilt cy-linder and will not permit the bucket to dump.Make-Up ValvesThere are two make-up valves in the lift and tiltcontrol valve. Make-up valve (19) is in the rod end ofthe lift circuit and make-up valve (4) is in the rod endof the tilt circuit. The make-up valves will permit oil21. Spring.24. Paasage.22. Passage to rod end of25. Load check valve for liftlift cylinders.circuit.23. Passage to head end of26. Spring.lift cylinders,27. Chamber.from the return line to add with pump oil when thecylinder rods are retracted faster than the pump cansupply oil to the cylinders. The make-up valves makesure that there is enough oil available so that there isno cavitation (vacuum) in the cylinders.Make-up valve (4) operates when the rod end ofthe tilt cylinder is retracted fast when the bucket isdumped. When the pressure in passage (5) decreasesenough, the pressure in passage (13) will becomegreater than the force of spring (3). Make-up valve(4) will move up and oil from passage (13) will gointo passage (5) and add to the oil in the rod end ofthe tilt cylinder. Make-up valve (4) will operate inthe same way when an outside force on the bucketcauses the tilt cylinder to be retracted.During LOWER operation, make-up valve (19)operates-the same way as make-up valve (4). DuringFLOAT operation, make-up valve ( 19) provides thefloat operation of the lift circuit (see FLOATOperation).3-106
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