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MAGM 262

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MAGM 262

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    2. Getting Started Effective troubleshooting involves more that hooking up a tester and taking readings. Start by thinking. Get all of the facts and examine them until you have pinpointed the trouble. Then check your diagnosis by testing in and only then start replacing parts.

    3. The Professional Troubleshooter An understanding of hydraulic components An understanding of hydraulic systems An understanding of hydraulic symbols An understanding of circuit diagrams An understanding of testing and diagnostic tools.

    4. Key Points Look for the easy things first Oil level and type Filter Do a fast check of pressure and flow Plumb at remotes OK for now If you indicated a flow problem then you must do a complete system check.

    5. Logical Diagnosis steps Question the operator ID exact symptoms of each problem. What happens and under what conditions? Determine what is working. Safety first ID and repair any unsafe working conditions. If the owner refuses note on work order and have them sign it! Physical examination Use eye, ears, nose, and hands. Check connections, external defects, fluid levels, filters, linkages, and records. Simulate problem If possible have operator simulate the problem while you observe. Verify Verify the performance of the major systems buy running tests and begin to eliminate systems that are within specifications.

    6. Logical Diagnosis steps Perform specific tests based upon findings. Perform tests using pressure gauges, flow meters, and hand pumps. To determine which components are working. Make repairs and re-test to verify

    7. Using a Hydraulic Tester After the preliminary assessments have been made you can now begin specific test to pinpoint the failure. Though specific situations vary we will discuss some basic procedures. Testers can be used to check entire system or individual components. By comparing the flow at no load and at rated psi you can determine: Slippage fluid leaking past worn pumps Valve leakage fluid leaking back to tank through leaking passages Internal leakage fluid leaking past cylinder or motor parts.

    8. Testing the hydraulic pump To test the pump, open the circuit and attach the inlet port of the tester to the outlet port of the pump. Connect the outlet from the tester directly back to the reservoir or low pressure return line. With system at operating temp (+120) and speed read and record pump flow at no load (0psi). Check flow at 250psi intervals and look for trends. Check flow at full working pressure. The difference between full pressure and 0 pressure is the internal pump leakage. Up to 15% leakage is acceptable. More than 30% indicates a badly worn pump.

    9. Testing the hydraulic pump If while testing the flow gauge needle bounces erratically it indicates pump cavitation. Cavitating is caused by: Air leak in pump suction line Sharp bend or break in suction line Clogged filter Low fluid level If you find reduced flow levels at both no load and full load this normally indicates an inlet line restriction but a minor one. Cavitation a condition where liquid does not entirely fill the existing space and the creation of vapor bubbles due to an excessive low pressure area. These bubbles can cause significant pump wear.

    10. The T Test The T test can determine. Pump efficiency Relief valve Cracking point too low Full relief too low Worn seats, seals, weak springs. Valve spool leakage Cylinder leakage

    11. The T Test Connect the tester by utilizing a T fitting connected between the pump outlet and the control valve. The tester output is routed to the tank. In addition a separate shut off valve should be located between the T fitting and the control valve. This will allow for the isolation of the pump from the rest of the system. Bring the hydraulic fluid up to operating temperature.

    12. The T Test Suction Line problems Open the tester load valve and close the shut-off valve. Start the engine and run at specified speed. Read and record the pump flow in GPM. If the no-load reading is equal to the specification the suction line is considered OK. If the no-load reading is below specifications the suction line is clogged or leaking air. Now increase load with the tester valve until mid-range pressure shows on the pressure gauge. If the gauge reads the same and no needle deflection, the problem is suction restriction If the reading is the same but with pressure needle is unsteady or fluctuating the problem is air leakage.

    13. The T Test Pump performance test Close the shut-off valve, start engine, get fluid to operating temperature. Close the tester load valve until pressure gauge indicates the rated load reading. Read and record the flow in GPM Flow at rated load will be somewhat less that flow at no-load 10% reduction in flow is acceptable.

    14. The T Test Main relief test Open the shut-off valve and the tester load valve. Start engine and get oil to operating temp Operate the control valve for one of the circuits that indicates the least leakage. Allow the cylinder to reach the end of its stroke but continue to hold the valve open. Now gradually close the tester load valve until the flowmeter needle just starts to move downscale. This is the relief cracking pressure. Now close the tester load valve totally. This forces all of the pump flow through the relief valve. Note the tester pressure reading. This is the full open pressure specification The cracking pressure should be no more that 10% of the full open pressure.

    15. The T Test Circuit Leakage test Open the tester load valve and close the shut off valve. Start engine and get oil to operating temperature and run at rated speed. Close the tester load valve until the pressure gauge indicates a mid-range psi Record the flowmeter reading and then open the shut-off valve. Now operate a control valve to allow its actuator to go to the fully extended or retracted position. While holding the actuator check the flowmeter reading If both are the same you can assume no leakage in this part of the system If the readings are different the difference is the amount of circuit leakage. Move control valve to the opposite position and check this end of the circuit just as before. Repeat for all circuits of the system.

    16. Finish the Job After you have determined what the failure is fix it. Upon completion retest the system to be sure that you fixed the problem

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