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Do not operate or work on this machine unless you have read and understand the instructions and warnings in the Operation and Maintenance Manual. Failure to follow the instructions or heed the warnings could result in injury or death. Contact any Caterpillar dealer for replacement manuals. Proper care is your responsibility. |
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Hydraulic Pump Test
Pressure Test Tools
The 4C-4890 Hydraulic Test Fitting Gp can be used to perform pressure tests on the machine systems. Before any tests are performed, visually inspect the hydraulic system for oil leaks. Also, check for parts that have been damaged.
To receive accurate test results, the test must be performed when the hydraulic oil is at the normal operating temperature.
Note: The 4C-4890 Hydraulic Test Fitting Gp may require the use of metric adapters in order to check the pressures on the machine.
Checks During Operation
The checks during operation can be used in order to find a valve or a pump that is not working correctly.
The speed of the movement of the cylinder rod or the torque on a motor can be used to check the condition of the following components:
- Motors
- Cylinders
- Pumps
- Feel the cylinders as the cylinders extend and as the cylinders retract. The movement of the cylinders must be smooth and regular.
- Listen for noise from the pumps.
- Listen for the opening of the relief valves. Relief pressures that are too low will cause reduced force of all functions. Relief pressure will also cause an increase in oil temperature and in the time of the operating cycle of the functions.
Note: Opening pressures that are too high will cause a decrease in the service life of the hoses and of the components.
- Be cautious of the drift rate in machine functions that are caused by the following situations:
- Cylinder leakage
- O-rings on the control valve
- Valves that do not seal properly
- Poor adjustment of the pilot valve
- Poor adjustment of the main valve
- Cylinder leakage
Pump Efficiency Check (Determining Flow Loss)
This test is designed to determine whether a pump is operating within design parameters.
For any pump test, the pump flow at 690 kPa (100 psi) will be larger than the pump flow at 6900 kPa (1000 psi) if the pump is operating at the same rpm. The pump flow is measured in L/min (US gpm).
The difference between the pump flow of two operating pressures is the flow loss.
Flow loss that is expressed as a percentage of pump flow is used as a measure of pump performance.
If the percent of flow loss is greater than 10%, the pump performance is inadequate.
Typical Examples
Note: The values in the examples are not set values for any specific pump or for any specific pump condition. See the Specification for your machine for the pump flow of a new pump at 690 kPa (100 psi) and at 6900 kPa (1000 psi).
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| Illustration 1 | g00919740 |
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| Illustration 2 | g00919746 |
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| Illustration 3 | g00919746 |
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| Illustration 4 | g00919762 |
Testing the Pump on the Machine
Install a flow meter. Run the engine at high idle. Measure the pump flow at 690 kPa (100 psi) and at 6900 kPa (1000 psi). Use these values in the following formula.
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| Illustration 5 | g00919767 |
Bench Testing the Pump
Use the following formula to determine the percentage of flow loss. Proceed if the following conditions are met:
- Flow rate of 6900 kPa (1000 psi)
- Pump at full rpm
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| Illustration 6 | g00919774 |
If the bench test cannot be performed at 6900 kPa (1000 psi) or at full pump rpm, run the pump shaft at 1000 rpm. Measure the pump flow at 690 kPa (100 psi) and at 6900 kPa (1000 psi). Use these values in the top portion of the following formula. For the bottom part of the formula, run the pump shaft at 2000 rpm. Measure the pump flow at 690 kPa (100 psi).