This motor test is probably one of the most simple, straightforward tests for hydraulic components. It can be executed with the highest degree of safety. Here is an outline of how a motor case flow test should be conducted:

1. Install a suitable flow meter in the case drain line, Figure 2.

2. Operate the machine (if possible) until the oil temperature is normal — approximately 130° F.

3. Operate the machine at no-load (nominal pressure), and record the no-load flow and pressure.

4. Operate the machine at full load (maximum pressure), and record the full-load flow and pressure.

5. Check the no-load flow against the full-load flow, and see that it is within recommended specifications. A good go/no-go rule-of-thumb is that if the full-load flow exceeds the no-load flow by approximately 25%, the leakage is excessive.

Note: using case flow tests exclusively to determine wear in hydraulic pumps and motors is not recommended. It does not detect wear between the barrel and the port/wear plate, and can therefore mask a significant amount of leakage that is not detectable in the case drain line.

Training — Training is the most significant vehicle for improving safety in all walks of life. As you will witness through this series of articles, ignorance is the root cause of almost all accidents associated with hydraulics. The fact that this test procedure was actually published in a service manual — and probably found its way into the hands of unsuspecting people (possibly all over the world) — is testimony to the fact that ignorance in the fluid power industry is far reaching.

Safety information — It was inevitable that someone following this procedure would get hurt. However, the recommendations neglected to mention additional crucial safety information which, although not directly related to the task at hand, should always be reinforced:

• lockout and tagout — critical

• safety glasses — critical

• proper diagnostic tools — critical

• proper skills — critical, and

• names of contacts for technical assistance — important.

Do not compromise — Machinery and equipment manufacturers sometimes assume that the customer will not have the proper tools to do the job. Consequently, they may offer a compromise. For example, remove a hose and “see” the flow, instead of using a flow meter. Or, crack a line to “see” for pressure, instead of using a pressure gage.

Manufacturers should state emphatically in their verbal and written communication, that if a person does not have the proper training and/or tools, they must not attempt to do the test. They should also point out the consequences of failing to follow safety recommendations.

Job safety breakdown — Machinery and equipment manufacturers should provide detailed Job safety breakdowns for the machinery they design and build.

Lead by example — Technical representatives from machinery or equipment manufacturers are extremely influential people. If they set a good example for safety in the field, others will follow. Not only must they abide by their own safety rules and procedures, but they must also respect those of their customers.

If they service a customer’s machine, they must have with them the proper diagnostic tools and equipment. If they are working with a customer’s personnel, they must continuously reinforce safety and tell what they are doing and why. The hard-working people in our plants and factories need all the help they can get — if you learn and know, share it with the world!

Technical schools and colleges— The greatest incubator for safety is where minds go to learn — the classroom. Fluid power instructors themselves must learn how to execute safe test procedures so they can help others do the same.

Stress safety every day and for each and every step taken in a job— and never give up! Demonstrate that you really care about safety, and you may save a few lives. What can be more important than that?

Rory McLaren is president, Fluid Power Training Institute, Salt Lake City. For more information, call (801) 908-5456, email, or visit

Caution: Rory McLaren and the Fluid Power Training Institute do everything possible to ensure that the information and drawings contained in these reports are accurate and that the suggested procedures are deemed safe and reliable. However, these are general recommendations only and might not be applicable to all situations. You must have your engineering and service departments read these recommendations and make the necessary changes for your specific conditions.

The Fluid Power Training Institute is not responsible for actions taken by untrained or unauthorized persons. All hydraulic system service, repair, and troubleshooting should be conducted only by trained, authorized personnel.