November 15, 2005 

'Inside Hydraulics' Newsletter

1. Rapid cleaning of contaminated hydraulic systems
2. Advanced filter condition monitoring
3. Read hydraulic schematics - like the experts
4. Content for your web site or e-zine
5. Help us spread the word
6. Tell us what you think


Rapid cleaning of contaminated hydraulic systems

When a hydraulic component suffers a catastrophic failure, large amounts of metallic particles are generated. These particles circulate in the hydraulic fluid and in extreme cases, the increased contamination load can clog the system's filters, resulting in the circulation of unfiltered fluid.

Once dispersed throughout the system, these particles present a risk to replacement components and can cause costly, repeat failures. The challenge is to completely remove these debris from plumbing and heat exchangers with minimum interference to the system and as little down time as possible.

The Hot Flush power flushing system is an effective and efficient solution to this problem. Hot Flush employs a patented, instant-reversing system. This instant-reversing action provides a "scrubbing" effect, which aids particle dislodgment and removes varnish deposits - which reduce system efficiency.

Hot Flush power flushing unit

Hot Flush power flushing unit

A 28-micron inspection screen provides visual indication of the debris being cleaned from the system and also allows the operator to know when contaminants in this size range have been completely eliminated from the system. This is backed-up by an 8-micron final filter.

Hot Flush is used extensively by the automotive and aviation industry, military, government and in a multitude of other applications where oils are circulated through plumbing and heat exchangers. For more information, application photos and testimonials, go to , email or call 800-852-5713.

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Get 'Industrial Hydraulic Control'
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2.   Advanced filter condition monitoring

Continuous monitoring of the filter elements in a hydraulic system can provide valuable clues to the performance of the filter and the condition of the system. Before I discuss this, let's consider some of the advantages and disadvantages of common filter locations.

Pressure filtration

Locating filtering media in the pressure line provides maximum protection for components located immediately downstream. Filtration rates of two microns or less are possible, due to the pressure available to force fluid through the media. Filter efficiency is reduced by the presence of high flow velocities, and pressure and flow transients, which disturb trapped particles. The major disadvantage of pressure filtration is economic. Because the housings and elements (high-collapse type) must be designed to withstand system operating pressure, pressure filtration has the highest initial and ongoing cost.

Return filtration

The rationale for locating filtering media in the return line is this: if the reservoir and the fluid it contains start out clean and all air entering the reservoir and returning fluid is adequately filtered, then fluid cleanliness will be maintained. The other advantage of the return line as a filter location is that sufficient pressure is available to force fluid through fine media - typically 10 microns, but pressure is not high enough to complicate filter or housing design. This combined with relatively low flow velocity, means that a high degree of filtering efficiency can be achieved at an economical cost. For these reasons, return filtration is a feature of most hydraulic systems.

Off-line filtration

Off-line filtration enables continuous, multi-pass filtration at a controlled flow velocity and pressure drop, which results in high filtering efficiency. Filtration rates of two microns or less are possible, and water absorbent filters and heat exchangers can be included in the circuit for total fluid conditioning. Off-line filtration has a high initial cost, although this can often be justified on a life-of-machine cost basis.

Filter condition monitoring

Warning of filter-bypass is typically afforded by visual or electric clogging-indicators. These devices indicate when pressure drop (delta P) across the element is approaching the opening pressure of the bypass valve (where fitted). In the case of a return filter for example, if the bypass valve opens at a delta P of 3 Bar, the clogging indicator will typically switch at 2 Bar.

Advanced filter condition monitoring

Replacing standard clogging-indicators with differential pressure gauges or transducers enables continuous, condition monitoring of the filter element. This permits trending of fluid cleanliness against filter element pressure-drop, which can be used to optimize oil sample and filter change intervals. For example, the optimal change for a return filter in a particular system could be higher or lower than the clogging indicator switching pressure of 2 Bar.

Continuous monitoring of filter pressure drop can also provide early warning of component failures and element rupture. For example, if the delta P across a pressure filter suddenly increased from 1 to 3 Bar (all other things equal), this could be an indication of an imminent failure of a component upstream. Similarly, a sudden decrease in delta P could indicate a rupture in the element - something that a standard clogging indicator will not warn of.

"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.   Read hydraulic schematics - like the experts

A schematic diagram is a 'road map' of the hydraulic system. The ability to read and interpret one can save a lot of time and effort when troubleshooting hydraulic problems. How to Read Hydraulic Schematics was developed by JI Case to teach their technicians how to read and understand hydraulic circuit diagrams. Find out more

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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