| Required Tools | |
| Part Number | Description |
| 198-4240 | Digital Pressure Indicator |
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Escaping fluid under pressure, even a pinhole size leak, can penetrate body tissue, causing serious injury, and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury. Always use a board or cardboard when checking for a leak. |
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Personal injury or death can result if two persons are not used in the following procedure. |
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| NOTICE |
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Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates. |
"Procedure 1" is a quick method for checking the cut-out pressure. This procedure also indicates whether the brake accumulator pressure switch and the brake oil pressure indicator operate correctly. The procedure provides an estimate of the accumulator precharge pressure and an estimate of the number of brake applications before the brake oil pressure indicator turns on.
"Procedure 2" determines whether the cut-in pressure and the cut-out pressure are correct. This procedure also provides the required steps for adjusting the brake accumulator charging valve.
Procedure 1
- Stop the engine. Engage the parking brake. Depress the brake pedal until there is no brake oil pressure.
- Connect a 0 to 20700 kPa (0 to 3000 psi) pressure gauge at the pressure tap for the front service brake accumulator (2) on brake accumulator charging valve (3) .
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| Illustration 1 | g00544512 |
Location of Accumulator Charging Valve and Pressure Taps (1) Pressure tap for rear service brake accumulator. (2) Pressure tap for the front service brake accumulator. (3) Accumulator charging valve. | |
- Observe the pressure gauge. Before the engine is started, the oil pressure must be 0 kPa (0 psi).
- Start the engine. Allow the oil pressure to increase to the cut-out pressure. The correct cut-out pressure should be 14485 ± 345 kPa (2100 ± 50 psi).
- After the brake accumulators have been completely charged and the correct cut-out pressure has been obtained, stop the engine.
- Turn the engine key start switch to the ON position, but do not start the engine.
- Apply the service brakes repeatedly. Pause for two seconds before each brake application and count the number of applications while you observe the pressure gauge.
- When the reading on the pressure gauge decreases to 8960 ± 345 kPa (1300 ± 50 psi), brake oil pressure indicator (4) will turn on. This indicates the operational status of brake oil pressure indicator (4). This also indicates the operational status of the brake accumulator pressure switch.
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| Illustration 2 | g00544591 |
Caterpillar Monitoring System (4) Low oil pressure indicator for the brake system. | |
- Continue to apply the service brakes. Pause for two seconds before each brake application. When the pressure drops off rapidly, this indicates the approximate nitrogen precharge pressure in the brake accumulators.
- Determine the number of brake applications that were required before the sudden pressure drop in Step 9. This number should be approximately 30 times.
- If the cut-out pressure is not within the specification, complete Steps 7 through 12 in "Procedure 2". If the nitrogen precharge pressure is not within the specification, refer to Testing and Adjusting, "Brake Accumulator - Test and Charge" for the machine that is being serviced.
- If the cut-out pressure and the precharge pressure are within the specification, connect the pressure gauge at the pressure tap for the rear service brake accumulator (1). Repeat Steps 1 through 11.
Procedure 2
- Stop the engine. Engage the parking brake. Depress the brake pedal repeatedly until there is no brake oil pressure.
- Connect a 0 to 20700 kPa (0 to 3000 psi) pressure gauge at the pressure tap for the front service brake accumulator (2) on brake accumulator charging valve (3) .
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| Illustration 3 | g00902895 |
Location of Accumulator Charging Valve and Pressure Taps (1) Pressure tap for rear service brake accumulator. (2) Pressure tap for the front service brake accumulator. (3) Accumulator charging valve. (5) Cover for the adjustment screw. | |
- Observe the pressure gauge. Before you start the engine, the oil pressure must be 0 kPa (0 psi).
- Start the engine and immediately raise the engine speed to high idle. Watch for a pause in the increase of oil pressure. Record the reading on the pressure gauge when this occurs. This is the approximate nitrogen precharge pressure in the brake accumulators. If the nitrogen precharge pressure is not within the specification, refer to Testing and Adjusting, "Brake Accumulator - Test and Charge" for the machine that is being serviced.
- The oil pressure must increase to a maximum. Record this pressure. This is the cut-out pressure of the brake accumulator charging valve. The correct cut-out pressure should be 14485 ± 345 kPa (2100 ± 50 psi).
- With the engine in operation, slowly apply the service brakes. Apply the service brakes several times in succession. Verify that the pressure drops consistently. At the point of the specified cut-in, the pressure begins to increase quickly. The cut-in pressure should be 11895 ± 345 kPa (1725 ± 50 psi).
- If the cut-in pressure and the cut-out pressure are not within the specification, stop the engine and completely release all oil pressure from the brake circuit by depressing the brake pedal repeatedly. Loosen the hydraulic tank filler cap in order to make sure that there is no residual pressure in the hydraulic oil tank.
- Remove the cover for the adjustment screw (5) .
- Turn the hex plug under cover (5) by a quarter turn. Turning the hex plug clockwise will increase the cut-in pressure and the cut-out pressure. Turning the hex plug counterclockwise will decrease the cut-in pressure and the cut-out pressure.
Note: The charging limits will move together. The range between cut-in pressure and the cut-out pressure is not adjustable.
- Install the cover for the adjustment screw (5) and tighten the hydraulic tank filler cap.
- Start the engine. Make sure that the cut-in pressure and the cut-out pressure are within the specification. If the pressures are not within the specification, repeat Steps 7 through 11.
- If the cut-in pressure and the cut-out pressure cannot be adjusted within the specification, the brake accumulator charging valve may need to be repaired or replaced.