How to avoid hydraulic troubleshooting mistakes

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Troubleshooting hydraulic systems can be a complex exercise. It involves a lot of science and sometimes, a bit of art. Incorrect diagnosis prolongs downtime and can result in the unnecessary repair or replacement of serviceable components. To avoid these costly mistakes, the correct equipment and a logical approach are required.

Assess the problem and eliminate the obvious

Before you incur the expense of hiring a technician, assess the problem and eliminate all of the obvious, possible causes. I have lost count of the number of times that I've been called to a problem and found that the cause was something quite simple. A wire broken off a solenoid valve, a pin fallen out of a mechanical linkage, an isolation valve that had vibrated closed, a blocked heat exchanger... and so the list goes on.

Your oversight won't bother the technician, because his hourly rate is the same, regardless of how easy or difficult the problem is to find. But you may be annoyed with yourself for not checking something so obvious, knowing that you could have easily saved the cost of the call-out.

Quality is more important than quantity

Paying for a technician's time when it is not required is certainly not desirable. But it is nowhere near as costly as paying for the unnecessary repair or replacement of serviceable components, as a result of incorrect diagnosis of a problem. Incorrect diagnosis in a troubleshooting situation is usually the result of the technician's incompetence, insufficient investigation of the problem or a combination of both.

Unfortunately it is not possible to determine a technician's competency from the badge on his shirt or his charge-out rate. While charge-out rates may be a factor in deciding whose technician you hire, from an overall cost perspective it is far more important to evaluate the technician and his diagnosis, so that you don't end up paying for his mistakes.

Let me illustrate how this can happen with an example. Several years ago, I was asked for a second opinion on the condition of a set of pumps operating a processing plant. The customer had called in a technician to check the performance of these pumps and was alarmed when the technician advised that all four pumps were in need of repair.

The pumps in question were variable-displacement units fitted with constant power control. The power required to drive a hydraulic pump is a product of flow and pressure. A constant power or power limiting control operates by reducing the displacement, and therefore flow, from the pump as pressure increases, so that the power rating of the prime mover is not exceeded.

Pump performance is checked using a flow-tester to load the pump and measure its flow rate. As resistance to flow is increased, pressure increases and the flow available from the pump to do useful work decreases because of internal leakage. The difference in the measured flow rate between no load and full load determines the volume of internal leakage and therefore pump performance.

I tested all four pumps, recording flow against pressure from no load through to maximum working pressure. In my report I explained to the customer that the tests revealed that pump flow did decrease significantly as pressure increased, but that this is a normal characteristic of a pump fitted with constant power control. I further advised that apart from the constant power control requiring adjustment on two of the pumps, the performance of all four pumps was acceptable.

The first technician's assessment can only be explained by fraud or incompetence. I suspect it was the latter, with the technician failing to either establish or understand that the pumps he was testing were fitted with constant power control. This ignorance led to an incorrect interpretation of the test results. Whatever the explanation, the customer could have paid thousands of dollars for unnecessary repairs, if they had not sought a second opinion.


When you have a problem with your hydraulic equipment, carry out an informed assessment of the problem and eliminate the obvious before you call for a technician. And if you do need to hire a technician, be sure to evaluate the technician and his diagnosis so you don't end up paying for his on-the-job-training or worse, his mistakes!

Related articles:

The value of the humble hydraulic symbol
Understanding hydraulic load sensing control
Would you pass this simple hydraulics test?

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