August 2, 2006 

'Inside Hydraulics' Newsletter
http://www.hydraulicsupermarket.com


IN THIS ISSUE
1. Reliability intelligence: monitoring water in oil
2. Hydraulic cylinder troubleshooting
3. More hydraulic cylinder tips
4. Content for your web site or e-zine
5. Help us spread the word
6. Tell us what you think

1.

Reliability intelligence: monitoring water in oil

Water contamination of hydraulic and lubricating oils can cause serious damage to bearings and other lubricated components - often without the equipment user being aware that damage is occurring.

Water in hydraulic fluid:

  • Reduces lubricating film-strength, which leaves critical surfaces vulnerable to wear and corrosion.
  • Depletes some additives and reacts with others to form corrosive by-products that attack some metals.
  • Reduces filterability and clogs filters.
  • Increases air entrainment ability.
  • Increases the likelihood of cavitation.

Left unchecked, these problems can rapidly lead to costly breakdowns. The speed with which water-induced degradation can progress, means that in many applications, water contamination is a more serious threat to equipment reliability than particulate contamination. EESIFLO's EASZ-1 water in oil analyzer provides early warning of any increase in water content so that corrective action can be taken.

EESIFLO's EASZ-1 water in oil analyzer

The EASZ-1 Water in oil monitor.

The EASZ-1 is a temperature-compensated, microprocessor-based, loop-powered water in oil sensor that enables fast and reliable on-line detection and monitoring of water in oil - displayed as a percentage or ppm. The unit responds rapidly to a change in the resistive capacitance of the oil being monitored and its reliability is not affected by saturation. The EASZ-1 displays any change in water content immediately.

Virtually maintenance free, with no need for sensor change or annual factory calibration, the EASZ-1 is an affordable tool for monitoring and protecting hydraulic equipment. It can be used for on-line water monitoring, as a control instrument allowing separators and oil purifiers to be started when required and as a diagnostic or preventative device protecting critical systems from premature failure.

For more information, or to locate your nearest EESIFLO representative, go to www.eesiflo.com


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2.   Hydraulic cylinder troubleshooting

In last month's issue we exploded the myth about what causes a double-acting hydraulic cylinder to creep under load and examined ways to reduce the recurring cost of hydraulic cylinder repairs. If you missed this article or for a recap, it's available here.

This article generated a lot of mail. Some of our readers struggled with the concept of a double-acting cylinder holding its load without a piston seal. When you calculate the difference in oil volumes either side of the piston the concept becomes clear. But as one of our readers pointed out there are a couple of exceptions. The first is where a load is hanging on a double-acting cylinder. With the cylinder fully retracted, there is enough volume on the piston side to accept all the oil from the rod side. So if the piston seal is by-passing and the load is heavy enough to overcome the vacuum that will develop, the cylinder will creep. The second exception is a double-ended cylinder, due to the equal volumes on both sides of the piston.

And in response to the discussion on cylinder rod buckling loads, many of our readers wanted to know how to deal with bent rods in a repair situation:

Checking rod straightness

Rod straightness should always be checked when a hydraulic cylinder is being re-sealed or repaired. This is done by placing the rod on rollers and measuring the run-out with a dial gauge (Figure 1). Position the rod so that the distance between the rollers (L) is as large as possible and measure the run-out at the mid-point between the rollers (L/2).

Checking Rod Straightness

Figure 1. Checking rod straightness.

Allowable run-out

The rod should be as straight as possible, but a run-out of 0.5 millimeters per linear meter of rod is generally considered acceptable. To calculate maximum, permissible run-out (measured at L/2) use the formula:

Run-out max. (mm) = 0.5xL/1000
Where: L equals distance between rollers in millimeters.

For example, if the distance between the rollers was 1.2 meters, then the maximum, allowable run-out measured at L/2 would be given by 0.5 x 1200 / 1000 = 0.6mm.

Dealing with bent rods

In most cases, bent rods can be straightened in a press. It is sometimes possible to straighten hydraulic cylinder rods without damaging the hard-chrome plating, however if the chrome is damaged, the rod must be either re-chromed or replaced.

If a rod is bent, then it is wise to check actual rod loading against permissible rod loading based on the cylinder's mounting arrangement and the tensile strength of the rod material. The formulas and procedure for doing this are explained in detail in Industrial Hydraulic Control. If actual road load exceeds permissible load then a new rod should be manufactured from higher tensile material and/or the rod diameter increased to prevent the rod from bending in service.


"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.   More hydraulic cylinder tips

For more hydraulic cylinder maintenance and repair tips, read Brendan Casey's article in the May-June 2006 Issue of Machinery Lubrication magazine, available here. To receive a complimentary subscription to this informative magazine (US and Canada only) go to: http://www.machinerylubrication.com/hydraulic1.asp


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 editor@hydraulicsupermarket.com 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: http://www.InsiderSecretsToHydraulics.com


5. Help us spread the word

If you've found our 'Inside Hydraulics' newsletter interesting and informative, then chances are you have a colleague who would too. Help spread the word about 'Inside Hydraulics' by forwarding this issue to a colleague. If they share your interest in hydraulics, then they will surely appreciate being told about this newsletter.

New subscribers can get the newsletter by completing the form at http://www.insidersecretstohydraulics.com


6. Tell us what you think

We would love to hear what you think of this issue of our 'Inside Hydraulics' newsletter. And of course, if you have any suggestions for future issues, please send us those too.

Just e-mail the editor at: newslettersuggestions@hydraulicsupermarket.com

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