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| Illustration 1 | g02846000 |
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Gear pump | |
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| Illustration 2 | g00424028 |
Idler gear (3) meshes with drive gear (1). The rotation of the two gears creates a partial vacuum. The partial vacuum is created at the pump inlet as the gear teeth separate. The vacuum draws the oil from the hydraulic tank. Oil enters the pump into cavity (4). The turning of the two gears causes the low-pressure oil from cavity (4) to move around the inner pump housing to cavity (2). As the teeth mesh at the outlet port, the oil is forced out of the gear pump.
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| Illustration 3 | g02715748 |
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(5) Shuttle Valve
(6) Relief valve (7) Pressure sensor (8) Brake accumulator charging valve (9) Screen (10) Priority valve (11) Brake and fan pump (12) Line from tank (13) Line to fan motor (14) Orifice (15) Check valve (16) Lines to accumulators | |
The brake and fan drive system contains a fixed displacement hydraulic pump. The brake system has priority over the fan drive system.
When the engine is started, hydraulic oil is drawn from tank (12) by brake and fan drive pump (11). Relief valve (6) is closed. Hydraulic oil flows from pump (11) to priority valve (10). Then, the hydraulic oil flows through priority valve (10) to the right side of the priority valve through brake accumulator charging valve (8). Oil also flows to the left side of the priority valve. The hydraulic oil and the spring pressure counter the pressure of the pilot oil that flows to the left side of the priority valve. The priority valve will hold to the left as the accumulators charge.
The priority valve directs hydraulic oil to screen (9). The oil flows through orifice (14) to check valve (15). As the hydraulic oil pressure increases, the check valve opens. The hydraulic oil flows to brake accumulator charging valve (8). Then, the oil flows to shuttle valve (5). The spring keeps brake accumulator charging valve (8) open. The shuttle valve directs hydraulic oil to the accumulator with the lowest pressure first. As the hydraulic oil pressure to the first accumulator increases, the shuttle valve moves. This movement allows both accumulators to charge at equal pressures. Hydraulic oil also flows to relief valve (6) through brake accumulator charging valve (8).
As the accumulators charge, hydraulic oil pressure increases to relief valve (6). When the hydraulic oil pressure overcomes the spring pressure on the relief valve, the relief valve moves down. The hydraulic oil to the right side of the priority valve drains to the inlet side of brake and fan drive pump (11). Then, the oil pressure on the left side of the priority valve moves the priority valve to the right. This movement directs most of the flow of hydraulic oil to the fan drive system. A small amount of hydraulic oil flows to the right side of the priority valve and to the relief valve. Because the relief valve is open, the oil flows to the inlet side of the pump.
When the priority valve moves to the right, the hydraulic oil pressure below check valve (15) decreases. Then, the check valve seats in order to maintain hydraulic oil pressure in brake accumulators (16). The shuttle valve (5) will move to the left or to the right. The lower accumulator pressure is directed to relief valve (6).
The flow of hydraulic oil from brake accumulators (16) is blocked at the brake control valve . When the brake pedal is pressed, the brake control valve routes hydraulic oil to the rear service brakes and to the front service brakes . This action engages the service brakes. Pressure feedback is sensed by each spool in the brake control valve. The operator will be able to feel the application of the service brakes. The pressure to the brake lines varies. As the brake pedals are depressed, the hydraulic oil pressure in the brake lines increases. Due to the spring below the bottom brake valve, maximum pressure to the front brakes is lower than the maximum pressure to the rear brakes.
When the accumulator charge pressure falls below the spring pressure on the relief valve, the relief valve moves up. This value is the cut-in pressure. Then, the accumulator charging cycle begins again.