A popular myth about hydraulic cylinders - exploded!

Hydraulic Supermarket logo

Earlier this year, I wrote an article for Machinery Lubrication magazine in which I debunked the myth that if the piston seal in a double-acting hydraulic cylinder is leaking, the piston rod will drift as oil slips past the seal. Fact is, it can't.

One reader, who couldn't grasp the concept, wrote the following to the magazine's editor:

"I will gladly eat my college diploma if Mr. Casey is correct in his assertion that:

"... if the piston seal is completely removed from a double-acting cylinder? the cylinder will hold its load indefinitely unless the rod-seal leaks."

"If what he said is correct, then why do we put seals on the pistons? Maybe the need for piston seals is just another "popular misconception".

I fear that Mr. Casey's assertion will not hold water any better than his cylinder (minus seals)."

Truly, this was the most entertaining reading I've had all week... better than the comics even."

Other people's ignorance rarely bothers me. But frankly I was steamed when I got this. For no other reason than, because his letter had come to me via the magazine's editor, I couldn't just ignore it.

So I hit reply and started typing. Pretty soon there was heat coming off my keyboard. After several minutes I stopped writing and thought to myself: "This is pointless. Because a man convinced against his will, is of the same opinion still."

Then I did what I should have done in the first place. I opened up my simulation software. And eight minutes later I had a model which demonstrates what actually happens in a double-acting hydraulic cylinder with a leaking piston seal. I made a video of it and sent copies to my skeptical reader and the editor of Machinery Lubrication.

This video is conclusive because seeing is believing. And it's definitely worth eight minutes of your time. Watch the video here.

Related articles:

How to troubleshoot hydraulic cylinder drift
How to test hydraulic cylinders
Solving hydraulic problems: whatever it takes?

If you enjoyed this article, you'll love Brendan Casey's Inside Hydraulics newsletter. It gives you real-life, how-to-do-it, nuts-and-bolts, hydraulics know-how -- information you can use today. Here's what a few members have said about it:

Can't Put It Down
?I get e-mails like this all the time. I never find time to read them. I decided to read Issue #30 and I couldn't put it down. I'll make time from now on.?

Richard A. Shade, CFPS, Project Engineer (Hydraulic Design), JLG Industries Inc.

So Valuable It Earned Me A Raise
?The knowledge I've gained from this newsletter has been so valuable it has earned me a raise!?

Jack Bergstrom, Heavy Equipment Mechanic, Sharpe Equipment Inc.

Love It - Keep Them Coming
?I just love this newsletter. As a Hydraulics Instructor for Eaton, I make copies and distribute them to my students as I address various topics. Please keep 'em coming.?

Michael S Lawrence, Hydraulics Instructor, Eaton Hydraulics Inc.

To get your FREE subscription ($149 value), simply type your first name and primary email address into the form below and hit 'SUBSCRIBE NOW!'

YES, I want to improve my hydraulics knowledge!

This is a private mailing list that will NEVER be shared for any reason.
You can also unsubscribe at anytime.

Home Page

Copyright © 2000 - 2013 Brendan Casey; HydraulicSupermarket.com