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1. |
Seal Saver - proactive maintenance for hydraulic cylinders |
Damaged cylinder rods and wiper seals are an eternal problem for users of hydraulic machinery.
Dents and gouges on the rods' surface reduce seal life and give dust and other contaminants an
easy path into the hydraulic system. These silt-sized particles act like lapping compound,
initiating a chain of wear in system components.
In response to this problem, a Marietta Georgia company, Fluid Control Services, Inc. has
developed and patented the Seal Saver protective cylinder cover. Seal Saver is not a typical
bellows boot you may already be familiar with. It is a continuous piece of durable material,
which wraps around the cylinder and is closed with Velcro. It is then clamped onto the cylinder
body and rod end. This makes installation simple with no disassembly of cylinder components
required.
Seal Saver forms a protective shroud over the cylinder rod as it strokes and prevents buildup
of contaminants around the wiper seal - a common cause of rod scoring, seal damage and
contaminant ingress. Research has shown that the cost to extract contaminants is ten times the
cost of exclusion. This, combined with the benefits of extended cylinder rod and seal life, makes
Seal Saver a cost-effective, proactive maintenance solution.
For more information, application photos, machine listings and a printable specification sheet,
visit www.sealsaver.com Alternatively, call 1-800-683-5189
or send an email to sealsave@mindspring.com
to request a complimentary Seal Saver video.
| 2. |
Hydraulic ram leak caused by operator error |
A client recently asked me to explain a seal failure on a hydraulic ram. The ram had been
removed from its machine due to a leaking rod seal, but upon inspection, both the rod seal and
the surface of the rod were found to be in serviceable condition.
What is a hydraulic ram?
A hydraulic ram is a single-acting cylinder in which fluid pressure acts on the cross-section
of the rod i.e. it has no piston (Figure 1).
Failure investigation
Because inspection of the rod seal (U-cup type) and the rod's surface didn't reveal any obvious
cause of failure, I asked the machine operator to describe the nature of the leak. He explained
that during his morning inspections he had noticed that there was always a trickle of hydraulic
fluid down the side of the ram.
Further investigation revealed that the current operator had only been assigned to the machine
several weeks earlier. So I asked the operator to explain how he left the machine at night. He
advised that after shutting down he always relaxed the hydraulics (released the load
off the ram). This revealed the most likely explanation for the nuisance leak.
Seal energization
To seal effectively, a U-cup seal relies on fluid pressure to energize the lips of the seal
against the rod and seal groove (Figure 1 inset). Releasing the load-induced pressure from the ram
after shutdown effectively de-energizes the seal. Once the seal is de-energized, a gradual
increase in the volume of fluid in the ram due to thermal expansion can result in fluid
leaking past the seal. This gradual loss of fluid prevents development of sufficient pressure
to effectively energize the seal, so the leak continues until the temperature, and therefore
volume, of the fluid in the ram stabilizes.
Root cause of failure
I advised my client that the practice of taking the load of the ram after shutdown was the most
likely cause of the leak. This being the case, there were two possible solutions. Stop
the practice or change the seal profile to an energized U-cup (a U-cup that has an O-ring
fitted in the 'U' to pre-energize the lips of the seal).
The root cause of the problem was confirmed when, without changing the seal profile, rod seal leakage was eliminated by
discontinuing the practice of unloading the ram.
Editors note - For more case studies like this one, join
Brendan Casey
for a practical, half-day workshop on troubleshooting hydraulic failures, to be held in
Nashville TN, March 21, 2004 and hosted by Lubrication Excellence 2004.
For more information, visit the LE2004 web site
or call 800-597-5460 or 918-749-1400
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"This book has the potential to save many
organizations lots of m0ney. It should be on the bookshelf of every engineer, supervisor, planner and
technician that deals with hydraulic equipment... it's worth its weight in gold." Find out more
Alexander (Sandy) Dunn
Plant Maintenance Resource Center
|
If you're involved or interested in the maintenance of hydraulic or any other type of
machinery, Machinery Lubrication magazine is highly recommended reading.
Keep up to date with machinery maintenance and reliabilty issues with a
complimentary subscription to this
informative magazine.
| 4. |
Content for your web site or e-zine
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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.
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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. |
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| 6. |
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