303C CR and 303.5C CR Mini Hydraulic Excavators Hydraulic System Caterpillar


Accumulator (Pilot) - Test and Charge

Usage:

303C CR BXT

------ WARNING! ------

Dry nitrogen is the only gas approved for use in the accumulators. The charging of oxygen gas in an accumulator will cause an explosion. An explosion can be eliminated by using nitrogen gas cylinders with standard CGA (Compressed Gas Association, Inc.) No. 580 connectors. When nitrogen gas is ordered, make sure to order the cylinders with CGA No. 580 connectors.

Do not rely on color codes or other methods of identification to tell the difference between nitrogen and oxygen cylinders. In any application, never use an adapter to connect your nitrogen charging group to a valve outlet used on both nitrogen, oxygen, or other gas cylinders. BE SURE YOU USE DRY NITROGEN (99.8% purity).

----------------------


NOTICE

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, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat products.

Dispose of all fluids according to local regulations and mandates.


Introduction

The accumulator stores pilot pressure oil for use at the main control valves. During multiple operations, the pilot system will demand more oil in order to maintain valve operation. The accumulator provides pilot pressure oil to the pilot system, when the pilot pump flow is inadequate. Inadequate flow will cause sluggish implement control.

Required Tools




Illustration 1g01089423

Tooling (A)




Illustration 2g02059473

Tooling group (D)

175-5507 Nitrogen Charging Group




Illustration 3g02103573

Tooling group (D) and (H)

175-5507 Nitrogen Charging Group

334-1071 Adapter for Accumulator Charging Assembly

9U-6740 Accumulator Charging Assembly

Table 1
Tool     Item     Part Number     Description     Qty    
A     A1     8T-0856     Pressure Gauge
(0 to 6,000 kPa (0 to 870 psi))    
1    
A2 6V-3989     Fitting     1    
A3 6V-4143     Quick Connect Coupler     2    
A4 177-7860     Hose As     1    
D     175-5507     Nitrogen Charging Group        
    D1     8S-4600     Nipple     2    
D2 8S-1506     Coupling     2    
D3 162-4147     Hose As     1    
D4 8S-4599     Coupling As     1    
D5 2S-5244     Fitting     1    
D6 1S-8937     Needle Valve     1    
D7 8T-0859     Pressure Gauge     1    
D8 162-4146     Regulator Assembly     1    
D9 7S-5106     Chuck     1    
D10 1S-8938     Air Chuck     1    
D11 2D-7325     Pipe Tee     1    
D12 1S-8941     Hose As     1    
H     9U-6740  (1)     Accumulator Charging Assembly     1    
    H1         Charging Valve     1    
H2     Charging Hose     1    
H3     Gauge     1    
H4 334-1071  (2)     Adapter     1    
( 1 ) Required for the 227-8807 Hydraulic Accumulator Gp
( 2 ) Adapter for 9U-6740 Accumulator Charging Assembly

Preliminary Test

  1. Start the engine. Place the hydraulic lockout lever in the UNLOCKED position.

  1. Position the implements 1 m (3.3 ft) from the ground.

  1. Shut off the engine by turning the start switch to the OFF position. When the engine has stopped, return the start switch to the ON position.

  1. Move the joysticks in order to lower the implements. When the accumulator circuit is functioning properly, there will be enough stored energy for approximately 1 minute after a power loss in order to lower the implements to the ground safely.

  1. If the preliminary test fails and the implements are unable to be lowered to the ground safely after a power loss, proceed to test the accumulator circuit. Refer to "Testing the Accumulator (Nitrogen Gas Charge)".

Testing the Accumulator (Nitrogen Gas Charge)

Note: Some accumulators do not have a charge pressure port. This type of accumulator cannot be recharged. The accumulator must be replaced. Replacement accumulators are equipped with a charge pressure port.




Illustration 4g02103574

Cap for charging port on accumulator

  1. Stop the engine. Release the pressure from the pilot hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".

  1. Make sure that valve (D6) is closed.

  1. Remove the cap from the accumulator.

  1. Rotate the valve handle on chuck (D9) or (D10) counterclockwise until the valve handle reaches the full out position. Install chuck (D9) or (D10) on the accumulator.

  1. Turn the valve handle clockwise until the valve is in the FULL OPEN position.

  1. Check the pressure reading on pressure gauge (D7) . Refer to Table 2 for the correct charging pressure and temperature relationship for the accumulator.

    Note: If the pressure reading is within the specifications of Table 2, continue to test the operation of the check valve within the pilot manifold. Refer to "Testing the Check Valve (Pilot Manifold)". If the pressure reading is too low or too high, refer to "Charging the Accumulator" to charge the accumulator before proceeding to test the operation of check valve within the pilot manifold.

Testing the Check Valve (Pilot Manifold)




Illustration 5g02194214

Check valve (top view of the pilot manifold)

If the check valve does not close properly during a loss of pilot pressure, the accumulator precharge pressure will exhaust before being able to provide lowering of the implements.

Note: Make sure that the accumulator has a proper nitrogen gas charge before attempting to test the check valve. An improperly charged accumulator may give indications of a problem with the check valve.

  1. Stop the engine. Release the pressure from the pilot hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".



    Illustration 6g02289553

    Pressure tap for the pilot manifold - 303C CR, 303.5C CR, 303.5D CR, and 304D CR




    Illustration 7g02194236

    Pressure tap for the pilot manifold - 304C CR, 305C CR, 305D CR, and 305.5D CR

  1. Connect a 6000 kPa (800 psi) pressure gauge to the pressure tap on the pilot manifold. Use tooling group (A) .

  1. Start the engine and place the hydraulic lockout lever in the UNLOCKED position.

  1. Shut off the engine by turning the start switch to the OFF position. When the engine has stopped, return the start switch to the ON position.

  1. After the power loss, the accumulator will still have pilot system pressure. Use the stopwatch to observe the pilot pressure. The pilot pressure should stay above 1035 kPa (150 psi) within 1 minute. This pressure ensures that enough stored energy is available to lower the implements to the ground.

    Note: When the pilot pressure in the accumulator is approximately 860 kPa (125 psi), the pressure will suddenly drop to zero. This sudden drop occurs because no oil is left in the accumulator.

  1. If the pilot pressure in the accumulator is below 1035 kPa (150 psi) or the pilot supply is exhausted in less than 1 minute, the check valve within the pilot manifold is not working properly.

  1. Move the joysticks in order to release any pilot hydraulic pressure in the accumulator.

  1. Turn off the engine.

  1. Clean the check valve. The check valve is located behind the plug on the pilot manifold. Repeat steps 3 through 5. If the test fails, replace the check valve.

Charging the Accumulator

Gas pressure is variable with temperature. Check the temperature of the air around the accumulator. In order to check the amount of charge in an accumulator, the accumulator must be at the same temperature as the surrounding air.

Note: The temperature of the accumulator may change as the accumulator is being charged due to the expansion or compression of the nitrogen charge. It may be necessary to charge the accumulator in several steps in order to ensure a correct charge.

Table 2
Charge Pressures and Temperatures    
Temperature     Pressure    

-25°C (-13°F)    

1490 kPa (216 psi)    

-20°C (-4°F)    

1520 kPa (220 psi)    

-15°C (5°F)    

1550 kPa (225 psi)    

-10°C (14°F)    

1580 kPa (229 psi)    

-5°C (23°F)    

1610 kPa (233 psi)    

0°C (32°F)    

1640 kPa (238 psi)    

5°C (41°F)    

1670 kPa (242 psi)    

10°C (50°F)    

1700 kPa (247 psi)    

15°C (59°F)    

1730 kPa (251 psi)    

20°C (68°F)    

1760 kPa (255 psi)    

25°C (77°F)    

1790 kPa (260 psi)    

30°C (86°F)    

1820 kPa (264 psi)    

35°C (95°F)    

1850 kPa (268 psi)    

40°C (104°F)    

1880 kPa (273 psi)    

45°C (113°F)    

1910 kPa (277 psi)    

50°C (122°F)    

1940 kPa (281 psi)    



Illustration 8g02103574

Cap for charging port on accumulator

  1. Stop the engine. Release the pressure from the pilot hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".

    Note: If an accumulator has less than half of the required amount of precharge pressure, the accumulator should be charged. Oil in the accumulator will give an inaccurate precharge reading.

  1. Make sure that valve (D6) is closed.

  1. Remove the cap from the accumulator.

  1. Rotate the valve handle on chuck (D9) or (D10) counterclockwise until the valve handle reaches the full out position. Install the chuck (D9) or (D10) on the accumulator.

  1. Turn the valve handle on the chuck (D9) or (D10) clockwise until the valve is in the FULL OPEN position.

  1. Check the pressure reading on pressure gauge (D7) . Refer to Table 2 for the correct charging pressure and temperature relationship for the accumulator.

  1. If the pressure reading on the gauge is too high, use the following steps in order to purge the nitrogen from the accumulator.

    1. Slowly open valve (D6) .

    1. Purge the nitrogen pressure until the pressure reading is within the specification.

    1. Close valve (D6) .

    1. Turn the valve handle on chuck (D9) or (D10) counterclockwise until the valve is in the FULL CLOSE position.

    1. Remove the test equipment. Replace the cap on the accumulator.

  1. If the pressure is too low, use the following procedure to charge the accumulator:

    1. Turn the valve handle on chuck (D9) or (D10) counterclockwise until the valve is in the FULL CLOSE position.

    1. Connect the tooling group (D) or tooling group (H) to the nitrogen cylinder with regulator assembly (D8) .

    1. Connect the other end of the hose to valve (D6) .

    1. Open the valve on the nitrogen cylinder. Make the appropriate adjustments to the regulator assembly until the gauge on the regulator indicates the proper precharge pressure for the accumulator. Refer to Table 2.

    1. Open valve (D6) . Loosen chuck (D9) or (D10) slightly. Allow the nitrogen to purge the air from the hose. Tighten chuck (D9) or (D10) .

    1. Turn the valve handle on chuck (D9) or (D10) clockwise in order to charge the accumulator.

    1. Close valve (D6) .

    1. The accumulator has the correct charge if the pressure on gauge (D7) and the pressure on the gauge on the regulator are equal and the gauge readings do not change. If there is a decrease in pressure on gauge for the regulator, open valve (D6) and allow more nitrogen to go into the accumulator.

    1. Repeat steps 8.d through 8.g until the following items occur:

      • The pressure on gauge (D7) is equal to the pressure on gauge on the regulator.

      • There is no pressure change when valve (D6) is closed.

      Note: If the accumulator will not maintain a nitrogen charge, the accumulator is damaged. Replace the accumulator.

      ReferenceThe replacement accumulator that comes from the factory is uncharged. Refer to Testing and Adjusting, "Charging the Accumulator" for the procedure to charge the replacement accumulator.

    1. Close valve (D6) . Close the valve on the nitrogen cylinder.

    1. Turn the valve handle on chuck (D9) or (D10) counterclockwise until the valve is in the FULL CLOSE position.

    1. Open valve (D6) . Loosen chuck (D9) or (D10) slightly in order to purge the nitrogen from the lines.

    1. Close valve (D6) .

    1. Remove the test equipment. Replace the cap on the accumulator.

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