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 NL O C A T I O N O F C H E C K V A L V E F O RP I L O T P R E S S U R E O IL1. Pilot pump section. 2. Check valve. 3. Line from selec-tor and pressure control valve.P I L O T S E C T I O N R E L I E F V A L VE1. Inlet. 2. Valve. 3. Drain outlet. 4. Poppet. 5. Passage.6 . S p r i n g . 7 . S p r i n g . 8 . O r i f i c e . 9 . O u t l e t . 1 0 . O r i f i c e .11. Housing.When pressures at inlet (1) and the chamber forspring (6) are the same, spring (6) holds valve (2)closed. During normal operation, the pressure frominlet (1) is more than the pressure in the chamberfor spring (6) because of a decrease in pressureacross orifice (10). This causes valve (2) to moveagainst the force of spring (6) and the extra oil frominlet (1) goes to drain outlet (3).When the pressure through outlet (9) gets too high thepressure causes poppet (4) to move against spring (7). The.oil in the chamber for spring (6) now goes throughpassage (5) and into drain outlet (3). There is now agreater differrence between the pressures on the ends ofthe valve (2). The valve moves farther against spring (6)and permits a larger amount of oil to go through drainoutlet.ONE-WAY CHECK VALVESThere are two one-way check valves in the imple-ment hydraulic system. These valves permit theflow of oil in one direction only. Check valve (2)is in line (3) between the selector and pressure con-trol valve and pilot pump section (1). Check valve(4) is in line (5) between the head end of the liftcylinders and the selector and pressure controlvalve.L O C A T I O N O F C H E C K V A L V E F ORH E A D E N D L I F T C Y L I N D E R O I L(View from under machine)4. Check valve. 5. Line from selector and pressure controlvalve.During normal machine operation, check valve(2) opens and lets pilot pressure oil go to the selectorand pressure control valve for operation of thepilot valves. Check valve (4) will not let pilot pres-sure oil go into the head end of the lift cylinders.C O M P O N E N T S O F A C H E C K V A L VE6. Inlet passage. 7. Valve. S. Spring. 9. Holes. 10. Out-let passage.3-94
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