1800472, OPR, HYSTER, Hyster2, SRM

//-->.pos {position:absolute; z-index: 0; left: 0px; top: 0px;}INTRODUCTIONGENERALThis section has the description and operation of the hy-draulic brake system. The section also has repair proce-dures for most of the components of the brake system.Also seeTHE HYDRAULIC SYSTEM, 1900 SRM471or1900 SRM 492for more information on the hy-draulic system.These lift trucks have a hydraulic brake system. The347brake system uses the hydraulic fluid and several com-ponents from the hydraulic system of the lift truck. Themain parts of the system are the hydraulic pump, accu-mulator charge valve and accumulator, two pressure re-duction valves and two brake pedal valves. For the ser-vice brake system there are four brake calipers at thedrive wheels and an auxiliary caliper on the rotor on thedrive shaft. For the parking brake system there is a park-ing brake valve, pilot valve and a caliper on the driveshaft.589112106114121615138.9.10.11.12.13.14.15.16.H36.00–48.00C SHOWNH20.00–32.00F (H440–700F/FS) SIMILARSERVICE BRAKE CALIPERSPARKING BRAKE CALIPERSHUTTLE VALVEMANIFOLDAUXILIARY SERVICE BRAKE CALIPERSERVICE BRAKE PEDAL VALVEPILOT VALVEINCHING SPOOLS (TRANSMISSION)ACCUMULATOR1. ACCUMULATOR CHARGE VALVE2. PRESSURE REDUCTION VALVE10.3 MPa (1500 psi)3. RELAY VALVE4. PRESSURE REDUCTION VALVE2.1 MPa (300 psi)5. PARKING BRAKE VALVE6. INCHING/BRAKE PEDAL VALVE7. INCHING VALVEFIGURE 1. BRAKE SYSTEM DIAGRAM165A71112+ 24VOLTS131415AA81093433DVEE2021182319161730TT224CCHH329281D31FF3227262MM (J)24ELECTRICAL WIRE25••••••NOTE:Letters by lines are identification codes.Early production codes are in brackets.1. TANDEM HYDRAULIC PUMP2. ACCUMULATOR CHARGE VALVE3. PRESSURE REDUCTION VALVE2.1 MPa (300 psi)4. ACCUMULATOR5. PRESSURE REDUCTION VALVE10.3 MPa (1500 psi)6. CHECK PORT NO. 3, 10.3 MPa (1500 psi)7. PARKING BRAKE VALVE8. INCHING/BRAKE PEDAL VALVE9. INCHING VALVE10. PILOT VALVE11. LOW BRAKE PRESSURE SWITCH12. LOW PRESSURE ALARM AND LIGHT13. PARKING BRAKE LIGHT (APPLIED)14. SWITCH, PARKING BRAKE PRESSUREAND TRANSMISSION LOCK OUT15. TRANSMISSION LOCK OUT16. SERVICE BRAKE PEDAL VALVE17.18.19.20.21.22.23.24.25.26.27.28.29.30.31.32.33.34.SHUTTLE VALVEBRAKE LIGHT SWITCHINCHING CYLINDERPARKING BRAKE CALIPERSERVICE BRAKE CALIPERBRAKE MANIFOLDSEQUENCE VALVEAUXILIARY SERVICE BRAKE CALIPERRELAY VALVETO LIFT CIRCUITTO STEERING CIRCUITTO ATTACHMENT CONTROL VALVECHECK PORT NO. 2, 2.1 MPa (300 psi)TO REMOTE CONTROL VALVECHECK PORT NO. 4, 19.0 MPa (2750 psi)CHECK PORT, 2.6 MPa (380 psi)CHECK PORT, 13.8 MPa (2000 psi)FROM BASE OF LIFT CYLINDERSFIGURE 2. BRAKE SYSTEM SCHEMATIC, H20.00–32.00F (H440–700F/FS)28911+ 24V121314157251610265171827242146126251920302922223ELECTRICAL WIRE3281.2.3.4.5.6.7.8.9.10.11.12.13.14.2615.16.17.18.19.20.21.22.23.24.25.26.27.27.28.29.30.••••••TANDEM HYDRAULIC PUMPRELIEF VALVEACCUMULATOR CHARGE VALVECHECK VALVEPRESSURE REDUCTION VALVE2.1 MPa (300 psi)ACCUMULATORPRESSURE REDUCTION VALVE10.3 MPa (1500 psi)PARKING BRAKE VALVEPILOT VALVEINCHING/BRAKE PEDAL VALVELOW BRAKE PRESSURE SWITCHLOW PRESSURE ALARM AND LIGHTPARKING BRAKE APPLIED LIGHTSWITCH, PARKING BRAKE PRESSUREAND TRANSMISSION LOCK OUTTRANSMISSION LOCK OUTPARKING BRAKE CALIPERINCHING VALVEINCHING SPOOLS (TRANSMISSION)BRAKE LIGHT SWITCHSERVICE BRAKE CALIPERSSEQUENCE VALVE (LATE MODELS ONLY)RELAY VALVEAUXILIARY SERVICE BRAKE CALIPERSERVICE BRAKE PEDAL VALVESHUTTLE VALVETO LIFT TRUCK HYDRAULIC SYSTEMCHECK PORT, PRESSURE REDUCTIONVALVE, 2.1 MPa (300 psi)CHECK PORT, PRESSURE REDUCTIONVALVE, 10.3 MPa (1500 psi)HYDRAULIC TANKCHECK PORT, ACCUMULATOR CHARGEVALVE AND RELIEF VALVECHECK PORT, 2.6 MPa (380 psi)FIGURE 3. BRAKE SYSTEM SCHEMATIC, H36.00–48.00C (H800–1050C)3DESCRIPTION AND OPERATIONH20.00–32.00F (H440–700F/FS)(See FIGURE 1. and FIGURE 2.)The small section of the tandem pump supplies the oil tooperate the brake system. Oil from the pump goes to theaccumulator charge valve. (Oil that is not needed by thebrake circuit flows to a control valve in the lift system.)From the accumulator charge valve, oil flows to the ac-cumulator, the pressure reduction valves and the brakepedal valves. The accumulator stores oil to operate thebrakes when the engine is not running. The pressure re-duction valve set at 2.1 MPa (300 psi) supplies oil to theparking brake valve, inching valve and the remote con-trol valve. The pressure reduction valve set at 10.3 MPa(1500 psi) supplies oil to the pilot valve for the parkingbrake caliper. There is a pressure switch connected tothis pressure reduction valve. Oil pressure holds theswitch open. When the oil pressure is less than (1300psi), the switch closes, actuating the low pressure alarmand light. The service brake pedal controls the flow ofoil to the service brakes. The inching brake pedal con-trols the flow of oil to the service brakes and the inchingspool at the transmission.controls the flow of oil to the service brakes and theinching spools at the transmission.ACCUMULATOR CHARGE VALVE(See FIGURE 4.)The accumulator charge valve controls the charging rateand the pressure of the oil in the accumulator for thebrake system. This valve also supplies oil to the twopressure reduction valves and the attachment controlvalve.The accumulator charge valve has a charging valvespool, check valve and a pilot valve assembly. Oil fromthe small section of the tandem pump enters the valve atthe charging valve spool. On the H36.00–48.00C(H800–1050C) units a relief valve limits this oil to 22.1MPa (3200 psi). Oil flows past the charging valve spool,through a screen and past a check valve to the accumu-lator and the pressure reduction valves. Oil also flows tothe attachment control valve. The accumulator chargevalve stops charging automatically when the accumula-tor pressure reaches its high limit of 18.6 to 19.3 MPa(2700 to 2800 psi). When the accumulator pressurereaches its low limit of 14.1 to 14.8 MPa (2050 to 2150psi), the accumulator charge valve allows oil from thepump to charge the accumulator. Two check valves inthe circuit keep the oil from flowing out of the accumu-lator.When the accumulator is charged above its lower limit,the charging valve spool is held against the stop by oilthat flows through the passage in the center of the spool.While in this position, the charging valve spool allowsmaximum flow to the control valve for the carriage andattachment (H36.00–48.00C/H800–1050C) or the liftsystem (H20.00–32.00F/H440–700F/FS). The checkball for the lower limit is held on its seat by oil pressureat the accumulator port.When the pressure in the accumulator reaches its lowerlimit, the pressure on the check ball for the lower limitdecreases and the check ball moves from its seat. At thissame time the pilot valve spool moves to let the checkball for the upper limit to stop against its seat. (The pilotvalve spool permits only one of the check balls to be onits seat at any time.) With the check ball for the lowerlimit off its seat, pressure from the accumulator can flowpast the pilot valve spool. The oil then flows through anorifice to the spring chamber for the charging valvespool.DESCRIPTION AND OPERATIONH36.00–48.00C (H800–1050C)(See FIGURE 1. and FIGURE 3.)The small section of the tandem pump supplies the oil tooperate the brake system. Oil from the pump goes to arelief valve and the accumulator charge valve. (Oil thatis not needed by the brake circuit flows to a control valvein the lift system.) The relief valve is set at 22.1 MPa(3200 psi). From the accumulator charge valve, oilflows to the accumulator, the pressure reduction valvesand the brake pedal valves. The accumulator stores oil tooperate the brakes when the engine is not running. Thepressure reduction valve set at 2.1 MPa (300 psi) sup-plies oil to the parking brake valve, inching valve andthe remote control valve. The pressure reduction valveset at 10.3 MPa (1500 psi) supplies oil to the pilot valvefor the parking brake caliper. There is a pressure switchconnected to this pressure reduction valve. Oil pressureholds the switch open. When the oil pressure is less than(1300 psi), the switch closes, actuating the low pressurealarm and light. The service brake pedal controls theflow of oil to the service brakes. The inching brake pedal417181210171615141812226A21201976T11P2212129132811.2.3.4.5.6.7.8.9.10.11.PLUGO–RINGPINSCREWSPRING, PILOTVALVEBALL RETAINERBALL, UPPER LIMITVALVE BODYSPOOL, CHARGINGVALVESPRINGSTOP12.13.14.15.16.17.18.19.20.WASHERFILTERSEATCHECK VALVESPRINGSCREW ASSEMBLYNUTSLEEVE10SPOOL, PILOTVALVE21. BALL, LOWER LIMIT22. SPRING119O5342112262122027PORTSA=TOACCUMULATORP=INLETPRESSURET=TODRAIN (TANK)O=FLOWTHROUGHFIGURE 4. ACCUMULATOR CHARGE VALVEThe oil pressure from the accumulator and the springpush the charging valve spool against the pressure fromthe inlet. The charging valve spool decreases the flow tothe control valve for the carriage and attachment(H36.00–48.00C/H800–1050C) or the lift system(H20.00–32.00F/H440–700F/FS), allowing the accu-mulator to charge.When the accumulator is charged to its upper limit, pres-sure will move the check ball for the upper limit from itsseat. At the same time, the check ball for the lower limitmoves to its seat. When the check ball for the upper limitis off its seat, the spring chamber for the charging valvespool is open to the drain circuit. The charging valvespool moves against the spring, allowing more oil toflow to the control valve for the carriage and attachment.When the operating pressure in the system is greaterthan the pressure in the accumulator, the check valvemoves from its seat. Oil from the pump can flow directlyto and charge the accumulator, bypassing the chargingvalve spool.PRESSURE REDUCTION VALVES(See FIGURE 8.)There are two pressure reduction valves in the hydraulicsystem. One of the pressure reduction valves controlsthe flow of oil to the pilot circuits for the following: re-mote control valve, the attachment control valve, theparking brake valve and the inching control valve. Thispressure reduction valve limits the pressure in the pilotcircuits to 2.1 MPa (300 psi). The other pressure reduc-tion valve limits the pressure to pilot valve for the park-ing brake caliper to 10.3 MPa (1500 psi).5

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