Fluid Power Safety Alert

Fluid Power Safety Alert


Unsafe service, repair, and troubleshooting recommendations are running rampant throughout the fluid power industry – and there is no end in sight! Make sure you are receiving your fluid power safety advice from a trusted and reliable source, then train your employees accordingly.


In this advisory, we are going to demonstrate how hazardous, documented, service, repair, and troubleshooting recommendations have proliferated the fluid power industry, leaving unsuspecting persons vulnerable to possible injury or death.

This flow-chart shows the proliferation of hazardous information, which is found primarily in service, repair, and troubleshooting documentation:

flow chart showing how hazardous, documented, service, repair, and troubleshooting recommendations proliferate the fluid power industry

We are also going to demonstrate the reality and severity of the problem by taking excerpts from a troubleshooting booklet written by a well-know publisher of fluid power textbooks. Their fluid power safety recommendations are entirely inaccurate and it is dangerous to take their advice.

We traced the information from its origin in Dallas, Texas, to a technical college in Vancouver, British Columbia, Canada. It then made its way into the service handbook of a coil-tubing machine manufacturer in Houston, Texas. It is given to literally hundreds of trainees yearly, as a reference manual by a national hydraulic training company.

Here are a number of excerpts from the original booklet:

Example 1 – Pump and Relief Valve Test

They recommend that you; “isolate the pump and relief valve from the circuit, so all you have is the pump, the relief valve, and a pressure gauge. Start the pump and dead-head the pump against the relief valve”.

This recommendation is unrealistic and impractical. Cannot be done if the pressure relief valve is integrated in the directional control valve housing. Applies to the majority of hand-operated valves.

They tell you to; “watch for pressure on the gauge while tightening the adjustment on the relief valve. If full pressure can be developed, obviously the pump and relief valve are operating correctly, and the trouble is to be found further down the line. If full pressure cannot be developed in this test, continue with step 3.”

Wrong! If the relief valve is worn, it can still be set at specified pressure – if the spool can be lifted, the valve can be set.

Example 2 – Pump or Relief Valve?

They recommend: “if high pressure cannot be obtained in step 2 by running the pump against the relief valve, further testing must be conducted to see whether the fault lies in the pump or in the relief valve”.

They recommend that you proceed as follows:
“If possible disconnect the reservoir return line from the relief valve. Attach a short length of hose to the relief valve outlet. Hold the open end of this hose over the reservoir filler opening so the rate of oil flow can be observed. Start the pump and run the relief valve adjustment up and down while observing the flow through the hose. If the pump is bad, there will probably be a full stream of oil when the relief valve adjustment is backed off, but this flow will diminish or stop as the adjustment is increased. If a flow meter is available the flow can be measured and compared with the pump catalog rating.”

An outrageous recommendation from a fluid power safety point of view. Too many unknowns! How much flow? Could the hose whip out of your hand? What if the oil discharging from the open hose strikes the top of the reservoir and sprays into your face? What is the temperature of the oil?

fluid power training, pump or relief valve

Then they recommend: “If a flow meter is not available the rate of flow on small pumps can be measured by discharging the hose into a bucket while timing with the sweep hand on a watch. For example, if a volume of 10 gallons is collected in 15 seconds, the pumping rate is 40 GPM, etc”.

Once again, you are discharging, who knows how much oil, at who knows what temperature to atmosphere – another fallacious recommendation!Technically wrong – it is physically impossible to properly test a hydraulic pump at no-load (low pressure).

With respect to pump and relief valve testing they recommend; “if the gauge pressure does not rise above a low value of say 100 PSI, and the volume of flow does not substantially decrease as the relief valve adjustment is tightened, the relief valve is at fault.”

The test concludes by their stating; “If the oil flow substantially decreases as the relief valve adjustment is tightened, and only a low or moderate pressure can be developed, this indicates trouble in the pump.”

Example 3 – Cylinder Testing

Their recommendation: “Run the piston to one end of its stroke and leave it stalled in this position under pressure. Crack the fitting on the same end of the cylinder to check for fluid leakage. After checking, tighten the fitting and run the piston to the opposite end of the barrel and repeat the test. Occasionally a cylinder will leak at one point in its stroke due to a scratch or dent in the barrel. Check suspected position in mid-stroke by installing a positive stop at the suspected position and run the piston rod against it for testing. Once in a great while a piston seal may leak intermittently. This is usually caused by a soft packing or o-ring moving slightly or rolling into different positions on the piston, and is more likely to happen on cylinders of large bore.

When making this test on hydraulic cylinders, the line should be completely removed from a cylinder port during the test, and the open line from the valve should be plugged or capped since a slight back pressure in the tank return line would spill oil from the line if not plugged. Pistons with metal ring seals can be expected to have a small amount of leakage across the rings, and even those “leaktight” soft seals may have a small bypass during break-in of new seals or after the seals are well worn.

Confusing! Which end of the cylinder is the “same end?”When installing a “positive stop” to check the “mid-stroke” position, should you not take into account the potential force output of the cylinder? A mechanic suffered an accident in which his nose was severed, and the majority of his front teeth were knocked out when he attempted to stall a hydraulic cylinder with a cable which snapped due to excessive force!

Once again, you are being told to “crack” a connector, or completely remove a transmission line, and check the condition of a hydraulic system that could operate at pressures up to 6,000 PSI and flows in excess of 100 GPM, to atmosphere. This recommendation is once again, absolutely fallacious!

fluid power training, cylinder testing

Example 4 – 4-Way Valve Testing (directional control valve)

For testing 4-way valves, either air or hydraulic, it is necessary to obtain access to the exhaust or tant return ports so that the amount of leakage can be observed. To make the test, disconnect both cylinder lines and plug these ports on the valve. Start up the system and shift the valve to one working position. Any flow out the exhausts or tank return line while the valve is under pressure is the amount of leakage. Repeat the test in all other working positions of the valve.

Once again, an outrageous and fallacious recommendation. This is one of the most ludicrous recommendations in this troubleshooting booklet. Consider what will happen if the valve has an open-center, or tandem-center spool configuration. When you start the system, what are you going to do with the “who-knows-how-much” oil, at the “who-knows-what” temperature?

NOTE: You would be well advised to refrain from doing the majority of the “tests” described in this troubleshooting booklet – you could get seriously injured or killed! DO NOT rewrite these procedures into your service, repair, and troubleshooting manuals. Any recommendation to exhaust hydraulic oil to atmosphere to “test” any and all hydraulic components is fallacious – the outcome is unpredictable!

Technical College – British Columbia, Canada

The same information, written literally word-for-word, shows up in a handout given to a millwright student in a technical college in British Columbia, Canada. He has to study the procedures, and pass a written exam to earn his millwright certificate. Upon graduation from college, he is hired by a local sawmill as a millwright, where his job is, amongst other things, to maintain the company’s various manufacturing machines, almost all of which are hydraulic.

Manufacturing Company – Houston, Texas

Now we trace the exact information, again, word-for-word, to a company that manufactures coil-tubing equipment in Houston, Texas. The potentially hazardous troubleshooting procedures show up in the company’s service and repair manual.

This information will be dispersed to poorly trained oil-field service mechanics who have to service, repair and troubleshoot the company’s vast fleet of oil-well service equipment.

Only one out of the three major oil-field service company’s makes hydraulic/fluid power safety training mandatory for all their maintenance employees.

National Hydraulic Training Company – U.S.A.

Literally thousands of these booklets find their way into people’s hands through schools and colleges. A national training company gives it to all of the people who attend their seminars. They claim to have trained over a quarter of a million people.


The author’s of hydraulic service, repair, and troubleshooting information, have a moral and ethical obligation to write proven, safety-based, information – what you recommend, is what people are going to do!

Here are some suggestions:

  1. The service, repair, and troubleshooting procedures that you write must be safe, reliable, accurate, practical, and proven.
  2. The information must pertain to the people who are going to use it. If it’s meant for field-service personnel, make it field-service oriented. Likewise, if it’s for engineers, make it engineering oriented.
  3. It is pointless giving the task of writing procedures for doing a task to a person who has never done that task before. If you have not personally done the job, you may overlook some vital steps, or make unrealistic recommendations.
  4. You may as well assume that the people who are going to use it are either not trained, or poorly trained. Hydraulics training for maintenance personnel is generally a privilege, not a requirement.
  5. Give as much information about fluid power safety as possible, e.g, lock the machine out, wear safety-glasses, etc.
  6. Absolutely no compromises! Don’t assume that the maintenance personnel have the proper diagnostic equipment – they probably do not! Insist that they either have the proper diagnostic equipment and know how to use it, or they simply don’t do the job.
  7. Make money! If you recommend that they use certain types of test equipment, THEY WILL purchase it from you. Don’t underestimate how much money you can generate by selling the right equipment for the right job.
  8. Lead by the most impeccable example. Follow the advice of your own technical services department, don’t take short cuts. Follow every safety rule, use the proper diagnostic equipment, and explain to untrained personnel who might be watching you, that you are trained to do your job, and that they, in your absence, should not try it.
  9. Before you decide what reference material is best for your students, read it yourself. Seek information that is safety-based, clearly written, and practical.


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