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| Illustration 1 | g00830393 |
Port Locations for the Accumulator Charging Valve (1) Accumulator port for the front brakes. (2) Accumulator port for the front brakes. (3) Port for the brake oil pressure switch. (4) Outlet to the hydraulic oil tank. (5) Pressure port. (6) Flow through port. (7) Adjustment screw cover. | |
The pilot/brake pump supplies hydraulic oil to the brake system. The oil first flows to the brake accumulator charging valve. The accumulator charging valve maintains the pressure in the accumulators at a constant pressure while the engine is running. If the machine has lost power or the hydraulic pump has failed, the pressure in the accumulators will permit several applications of the service brakes.
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| Illustration 2 | g00547481 |
Schematic of the Accumulator Charging Valve (1) Accumulator port for the rear brakes. (2) Accumulator port for the front brakes. (3) Port for the brake oil pressure switch. (4) Outlet for the implement and steering pilot oil. (5) Outlet to the hydraulic oil tank. (6) Inlet from the brake pump. (7) Pressure relief valve. (8) Unloading valve. (9) Check valve. (10) Spool for cut-in and cut-out pressure. (11) Inverse shuttle valve. | |
Note: The 836G Landfill Compactor is only equipped with front brakes. The accumulator port for the rear brakes of the 137-7038 Accumulator Charging Valve (1) is plugged. Also, the 137-7038 Accumulator Charging Valve is not equipped with an inverse shuttle valve (11) .
When the accumulator oil pressure decreases below 11725 ± 345 kPa (1700 ± 50 psi), the accumulator charging valve reaches the cut-in pressure setting.
When the accumulator charging valve is at the cut-in pressure setting, the combined force of the accumulator pressure and of the springs of inverse shuttle sections (11) is less than the pressure that is in the center of inverse shuttle section (11) .
The center pressure moves the two halves of inverse shuttle section (11) outward. This allows the hydraulic oil to flow to one accumulator or to both accumulators. In addition, the pilot/brake pump supplies pilot oil to the implement system. Any excess oil which is not required for these systems is diverted back to the hydraulic oil tank.
When the hydraulic oil flows from the accumulator charging valve to the accumulators, the pressure decreases between inverse shuttle section (11) and check valve (9). The pressure decrease allows the spring force to move spool (10). This causes hydraulic oil to flow to unloading valve (8). In this position, the orifice in unloading valve (8) restricts the pump flow to outlet (4). This also restricts the pump flow to the implement and steering pilot systems.
When the accumulator charging valve is at the cut-in pressure setting, the oil flows from inverse shuttle section (11) of the accumulator charging valve to port (3). Port (3) connects to a low brake oil pressure switch. The low brake oil pressure switch alerts the operator when the brake oil pressure drops below the minimum operating pressure.
Pump oil flows to the accumulators until inverse shuttle section (11) reaches the cut-out pressure setting. When the accumulator oil pressure increases to 14973 ± 345 kPa (2170 ± 50 psi), the accumulator charging valve reaches the cut-out pressure setting.
Note: The cut-out pressure setting of the accumulator charging valve for the 836G is 14485 ± 345 kPa (2100 ± 50 psi)
When the accumulator oil pressure increases to the cut-out pressure setting, the combined force of the oil pressure and of the springs in inverse shuttle section (11) is greater than the pressure that is in the center of inverse shuttle section (11). The pressure increase moves the two halves of inverse shuttle section (11) inward. This blocks the flow of hydraulic oil to the accumulators.
When the flow of oil to the accumulators is blocked, the supply pressure increases. The pressure increase causes spool (10) to overcome the spring force. This causes spool (10) to open a passage for oil to flow from unloading valve (8) to the tank.
When the pressure from spool (10) to unloading valve (8) decreases, unloading valve (8) overcomes the spring force. This causes pump oil to flow through unloading valve (8) to the implement and steering pilot systems.
Check valve (9) prevents high pressure oil from flowing from inverse shuttle section (11) and spool (10) to the implement and steering pilot systems.
The accumulator charging valve remains in the position of the cut-out pressure setting until the pressure in the accumulators decreases to the cut-in pressure setting of 11725 ± 345 kPa (1700 ± 50 psi).
Pressure relief valve (7) regulates the pressure of oil to the brake circuit. Any excess oil that is not required by the implement pilot circuit or the brake circuit is diverted back to the hydraulic oil tank. The pressure setting of relief valve (7) is 17240 ± 690 kPa (2500 ± 100 psi).