914G and 914G2 Compact Wheel Loaders and IT14G and IT14G2 Integrated Toolcarrier Hydraulic System Caterpillar

Pilot Accumulator

The following procedure can be used in order to test the pilot accumulator. The pilot accumulator maintains pressure in the pilot hydraulic system. The accumulator allows you to lower the boom, and the work tools with a stopped engine.

When you test or you charge the pilot accumulator, the pressure in the pilot hydraulic system must be released. The temperature of the nitrogen gas must also be taken into account. The pressure and volume of nitrogen gas varies with temperature.

Operational Test for the Pilot Accumulator

Illustration 1	g01043970
Location of pressure reducing valve

1. Turn the engine start switch to the ON position. Move the joystick and the control levers through the full range of travel. Repeat moving the levers several times.

   Note: Moving the joystick and moving the levers will release the pressure in the pressure reducing valve.

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Illustration 2	g01043973
(A) Pressure tap for pilot pressure

2. Install 198-4240 Digital Pressure Indicator to pressure tap (A) for the pilot pressure in the pressure reducing valve.

3. Start the engine and run the engine at HIGH idle. The digital pressure indicator should read 3150 ± 200 kPa (455 ± 29 psi).

4. Stop the engine. Turn the start switch to the ON position.

5. Move the joystick and the control levers through the full range of travel. Repeat moving the levers several times.

   Note: Moving the joystick and moving the levers will release the pressure in the pressure reducing valve.

6. Watch the digital pressure indicator as you move the joystick. The pressure will steadily decrease as you move the joystick.

7. When the pressure is approximately 850 kPa (125 psi) the pressure will suddenly drop to zero. This occurs because no oil is left in the accumulator. Note the final pressure before the sudden reduction of hydraulic pressure. The final pressure prior to the sudden drop to zero is the approximate pressure of the accumulator charge. If the final pressure is within specifications for the accumulator, stop. Charging the accumulator is not required.

Discharging the Accumulator

1. Ensure that the oil in the hydraulic system is at normal operating temperature. Park the machine on a smooth, level surface.

2. Install the steering frame lock. Block the wheels. Stop the engine.

3. Turn the engine start switch to the ON position. Move the joystick and the control levers through the full range of travel.

   Note: Moving the joystick and moving the levers will release the pressure in the pilot hydraulic system.

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Illustration 3	g01043975

4. Raise the door on the rear of the machine in order to access the pilot accumulator.

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Illustration 4	g01043976
Accumulator for the pilot valve

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Illustration 5	g01043978

5. Remove guard (1) which protects nitrogen charging valve (2) .

6. Remove the protective cap on nitrogen charging valve (2) .

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Illustration 6	g00282185
(3) Nipple. (4) Coupling assembly. (5) Pressure gauge. (6) Hose assembly. (7) Coupling assembly. (8) Nipple. (9) Valve. (10) Pressure gauge. (11) Regulator assembly. (12) Pressure regulating screw. (13) Chuck for the nitrogen cylinder valve. (14) Valve handle. (15) Nitrogen charging chuck. (16) Hose assembly. (17) Tee.

7. Identify the correct nitrogen charging chuck.

   Note: For a nitrogen charging valve with a .305 inch -32 THD, use a 1S-8938 Nitrogen Charging Chuck and a 1U-5551 Extension Assembly. For a nitrogen charging valve with a .482 inch -26 THD, use a 7S-5106 Nitrogen Charging Chuck and a 7S-5439 Extension Assembly .

8. Attach hose assembly (16) to nitrogen charging chuck (15) .

9. Turn the valve handle (14) on nitrogen charging chuck (15) all the way in the counterclockwise direction. This will ensure that nitrogen charging valve (2) will not be opened when nitrogen charging chuck (15) is attached to the nitrogen charging valve.

10. Attach nitrogen charging chuck (15) and hose assembly (16) to nitrogen charging valve (2) .

11. Attach nitrogen charging chuck (15) and hose assembly (16) to nitrogen charging valve (2) .

12. Place the open end of hose assembly (16) away from the work area and away from other personnel.

13. Turn valve handle (14) on nitrogen charging chuck (15) all the way in the clockwise direction in order to open nitrogen charging valve (2). This will release all of the compressed gas from the accumulator through hose assembly (16). Now, the accumulator can be removed from the machine.

14. Disconnect the hydraulic lines for servicing, as needed.

Nitrogen Charging Procedure

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Illustration 7	g00107133
Nitrogen Charging Group (1) Nipple. (2) Coupling assembly. (3) Pressure gauge. (4) Hose assembly. (5) Coupling assembly. (6) Nipple. (7) Valve. (8) Pressure gauge. (9) Regulator assembly. (10) Pressure regulating screw. (11) Chuck for the nitrogen cylinder valve. (12) Valve handle. (13) Chuck. (14) Hose assembly.

1. Ensure that valve (7) is closed. Install chuck (13) onto the pilot accumulator. Turn valve handle (12) completely in the clockwise direction.

2. If the reading on pressure gauge (8) is too high, slowly open valve (7) in order to lower the pressure. If the reading on the pressure gauge is too low, use the following procedure to charge the accumulator:

   1. Connect a hose from the nitrogen cylinder to chuck (11) .

   2. Open the valve on the nitrogen cylinder. Adjust screw (10) on regulator assembly (9) until pressure gauge (3) is at the correct charging pressure.

   3. Slowly open valve (7) and charge the accumulator. Charge the accumulator to 850 ± 68 kPa (125 ± 10 psi) at a temperature of 21 °C (70 °F). Then, close valve (7). If pressure gauge (8) and pressure gauge (3) show the same reading and the readings do not change, the accumulator has the correct charge.

      If the pressure reading on gauge (8) decreases, open valve (7) and allow more nitrogen to fill the accumulator.

      Perform this procedure until pressure gauge (8) and pressure gauge (3) show the same reading. Make sure that neither reading changes when valve (7) is closed.

3. Close valve (7). Close the valve on the nitrogen cylinder.

4. Turn valve (12) on chuck (13) outward in the counterclockwise direction. Remove the test equipment.