December 14, 2005 

'Inside Hydraulics' Newsletter

1. Pneumatic control for industrial automation
2. How to avoid costly troubleshooting mistakes
3. Selecting hydraulic connectors for reliable plumbing
4. Content for your web site or e-zine
5. Help us spread the word
6. Tell us what you think


Pneumatic control for industrial automation

An excellent book that effectively tackles the complex subject of pneumatics, by explaining the underlying operating principles and function of components and systems - for all levels of understanding, is now available in our online store.

It's called Pneumatic Control for Industrial Automation by Peter Rohner. This is not just another book covering basic pneumatic theory and concepts. Peter Rohner is a University Professor with over 30 years of teaching experience. He is one of the most successful fluid power lecturers and authors in the world today.

And even though the book's title is Pneumatic Control for Industrial Automation , the information it contains is just as relevant even if you aren't interested in the more advanced concepts of pneumatic control. Chapters 12 to 16 cover compressed air production, conditioning and distribution - important topics that are extremely relevant in most industrial workplaces.

There is something in this book for everyone - student, engineer and technician. For details of what's included in each chapter, and the powerful knowledge you'll gain, go here now:

Get a lifetime of hydraulics knowledge...

Get 'Industrial Hydraulic Control'
. Find out more

2.   How to avoid costly troubleshooting mistakes

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!

"Thanks for the great work on the two publications, Insider Secrets to Hydraulics and Preventing Hydraulic Failures. I have been in the hydraulics business for the past 20 years and it is very difficult to find any decent material on hydraulic maintenance, troubleshooting and failure analysis. These two books cover it all in easy to understand language... I conduct hydraulic training courses and plan to purchase copies to distribute to my students to share your practical approach to understanding a not so understandable subject."

Paul W. Craven, Certified Fluid Power Specialist
Motion Industries, Inc.

3.   Selecting hydraulic connectors for reliable plumbing

For guidance on selecting hydraulic connectors to achieve reliable plumbing, read Brendan Casey's article in the September-October 2005 Issue of Machinery Lubrication magazine, available here. To receive a complimentary subscription to this informative magazine (US and Canada only) go to:

4. Content for your web site or e-zine

Need some fresh content for your web site or e-zine? You now have permission to reprint these 'Inside Hydraulics' articles on your web site or in your e-zine, provided:

1. Each article is printed in its full form with no changes.

2. You send an e-mail to to advise us where you'll be publishing them.

3. You include the following acknowledgement at the end of each article:
About the Author: Brendan Casey has more than 16 years experience in the maintenance, repair and overhaul of mobile and industrial hydraulic equipment. For more information on reducing the operating cost and increasing the uptime of your hydraulic equipment, visit his web site:

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