VALVE GP-RELIEF 2722334 - Caterpillar

Sudden movement of the machine or release of oil under pressure can cause serious injury to persons on or near the machine.To prevent possible injury, perform the procedure that follows before testing and adjusting the hydraulic system.
Cold ambient temperatures could result in the loss of secondary braking capability due to inadequate hydraulic accumulator nitrogen pre-charge. The loss of the secondary braking system as well as the main hydraulic pressure will result in little or no braking capability and a potential for injury or death.It is recommended to perform a brake accumulator check anytime the machine has been idle for longer than two hours below −25 °C (−13 °F). Refer to Operation and Maintenance Manual before performing any check of the brake accumulator.
Specification
Table 1
Accumulator Precharge Pressure/Temperature Relationship for a Typical 8000 kPa (1160 psi) Brake Accumulator
Temperature Pressure(1)
0° C (32° F) 7454 kPa (1081 psi)
5° C (41° F) 7591 kPa (1101 psi)
10°C (50°F) 7727 kPa (11201 psi)
15° C (59.00000° F) 7864 kPa (1141 psi)
21°C (70°F) 8000 kPa (1160.32000 psi)
25° C (77° F) 8136 kPa (1180 psi)
30° C (86° F) 8273 kPa (1200 psi)
35° C (95° F) 8409 kPa (1220 psi)
40° C (104° F) 8546 kPa (1239 psi)
45° C (113° F) 8682 kPa (1259 psi)
(1) The tolerance on the nominal pressure is 345 kPa (50 psi).Introduction
The brake accumulators are mounted ahead of the right front wheel well. The purpose of the accumulator is to store pressure. This stored pressure will allow the machine operator to bring the machine to a stop in the event of an interruption of pressure from the brake pump.The following procedure will determine if the accumulator is charged to the appropriate pressure.Accumulator Charge Procedure
Refer to Special Instruction, REHS5464, "Accumulator Discharging and Charging Procedures". Lowering the Piston in Brake Accumulators
Hydraulic accumulator contains gas and oil under high pressure. Improper removal or repair procedures could cause severe injury. To remove or repair, instructions in the service manual must be followed. Special equipment is required for testing and charging.
Relieving the pressure in the brake circuit will not release the nitrogen precharge pressure in the brake accumulators.
Remove the pressure from the brake system by pumping the service brake pedal at a rate of one second ON and one second OFF. Continue to pump the brakes until the pressure at the TF port on the fan/brake manifold is less than 140 kPa (20 psi). Do not assume that the pressure is removed from the circuit if the brake pedal has no resistance. In order to charge the accumulator, the piston in the brake accumulator must be on the bottom of the cylinder. The air temperature outside the accumulator is the ambient temperature. Before the dry nitrogen pressure in the accumulator can be accurately checked, the temperature of the accumulator must be equal to the ambient temperature. Before the accumulator may be correctly charged, the temperature of the accumulator must be equal to the ambient temperature.Use Table 1 in order to determine the