A popular myth about hydraulic cylinders - exploded!

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.

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