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| Illustration 1 | g00878043 |
814F Accumulator Charging Valve and Schematic (1) Plug (2) Inverse shuttle valve (3) Cut-in, cut-out spool (4) Check valve (5) Charge rate orifice (6) Priority spool (7) Standby pressure spring (8) Adjustment screw (9) Pressure relief valve (A) Front brake accumulator port (B) Inlet port (C) Tank port (D) Rear brake accumulator port (E) Pressure switch port | |
The illustration shows the accumulator charging valve that is on the 814F Wheel Tractor. The accumulator charging valve on the 815F Soil Compactor and the 816F Landfill Compactor will charge the front axle brakes and the parking brake on the same circuit. Inverse shuttle valve (2) and rear accumulator port (D) are not present on that valve.
The brake accumulator charging valve controls the flow of oil from the pump to the brake circuits. The hydraulic oil is diverted, based on the pressure requirements of the brake circuits. Standby pressure spring (7) will also maintain a standby pressure of 2900 ± 140 kPa (420 ± 20 psi) in order to supply pressure for the implement pilot system.
When the engine is started, the accumulator charging valve receives the flow of oil from the pilot/brake pump at inlet port (B). Pressure relief valve (9) will cause the pump flow to return to the hydraulic tank if the oil pressure in the brake system exceeds 16550 ± 690 kPa (2400 ± 100 psi) during charging of the accumulators.
Priority spool (6) regulates the flow of oil through inverse shuttle valve (2) to the brake accumulators. Until the oil pressure reaches the cut-out pressure, priority spool (6) directs the oil to inverse shuttle valve (2) through charge rate orifice (5) and check valve (4). Charge rate orifice (5) allows the accumulators to fill at a controlled rate. Check valve (4) maintains the pressure in the brake circuit by preventing the high pressure oil in the accumulators from flowing back through priority spool (6). During charging, inverse shuttle valve (2) will allow flow to both accumulators. After reaching the cut-out pressure, inverse shuttle valve (2) allows the accumulator with the lowest pressure to act on cut-in, cut-out spool (3). Inverse shuttle valve (2) sends oil to pressure switch port (E) .
Cut-in, cut-out spool (3) controls the cut-in pressure and the cut-out pressure for the accumulator charging valve. When the cut-out pressure is reached, cut-in, cut-out spool (3) shifts and blocks pilot pressure for priority spool (6). Pilot pressure for priority spool (6) is drained to the hydraulic tank. This allows priority spool (6) to shift to the left and priority spool (6) reduces the restriction to oil flow to the hydraulic tank. Standby pressure spring (8) keeps priority spool (6) from shifting all the way to the left. Standby pressure spring (7) maintains the standby pressure in the pump. This provides the pressure for the pilot system. The pressure is now lower than the accumulator pressure. Check valve (4) will close.
When the service brakes are applied, oil from the accumulators is being used. The pressure in the accumulators will decrease. When the pressure in one of the accumulators drops below the cut-in pressure, cut-in, cut-out spool (3) will shift to the left. Cut-in, cutout spool (3) will send pilot pressure to priority spool (6). The pilot pressure will cause priority spool (6) to shift to the right. When this occurs, priority spool (6) will divert oil from the pump to the brake accumulators through inverse shuttle valve (2) .
Adjustment screw (8) will allow the cut-in pressure setting and the cut-out pressure setting to be changed.
Pressure switch port (E) connects to the brake oil pressure switch. The brake oil pressure switch sends a signal to the Caterpillar Monitoring System when the brake oil pressure drops below 8960 ± 537 kPa (1300 ± 75 psi).