Pressure intensification in hydraulic cylinders

Hydraulic Supermarket logo

A question that I'm asked regularly is "What is the best way to test the integrity of the piston seal in a double-acting hydraulic cylinder?"

There is a simple bench-test for doing this but it involves the intensification of pressure in the cylinder. While the test procedure is safe if you understand the concept of intensification in a hydraulic cylinder - it is inherently dangerous if you don't.

In this article I will explain the dangers of intensification in a double-acting cylinder and in this article I will explain the test procedure.

Cylinder force

Force produced by a hydraulic cylinder is a product of pressure and area (F = p x A). In a conventional double-acting cylinder the effective area and therefore force produced by the piston and rod sides of the cylinder are unequal. It follows that if the rod side of the cylinder has half the effective area of the piston side, it will produce half the force of the piston side for the same amount of pressure.

Pressure intensification

The equation F = p x A can be transposed as p = F/A that is, pressure equals force divided by area. If the rod side of the cylinder has to resist the force developed by the piston side, with only half the area, then it needs double the pressure. This means that if the piston side is pressurized to 3,000 PSI a pressure of 6,000 PSI will be required on the rod side to produce an equal force. This is why pressure intensification can occur in a double-acting cylinder. Note that pressurizing a cylinder rated at 3,000 PSI, to 6,000 PSI can have devastating consequences. Watch this 6-minute video for a better understanding of pressure intensification in a hydraulic cylinder.

If, for any reason, the piston side of a double-acting cylinder is pressurized and at the same time fluid is prevented from escaping from the rod side, pressure will increase (intensify) in the rod side of the cylinder until the forces become balanced or the cylinder fails catastrophically. Consider the following scenario one of our newsletter readers described to me recently:

"It was minus 36 degrees here the other day and we had a hydraulic cylinder at about minus 10 degrees. The boss was attempting to press out a pin. He turned on the pump and moved the lever. Next thing, the gland end of the cylinder blew out. It was a 7.5" cylinder with a 2,500 PSI operating pressure."

The gland on this hydraulic cylinder blew out as a result of pressure intensification. This was due to a blockage between the rod side of the cylinder and tank, as a result of the cold conditions. The ambient temperature had fallen below the pour point of the hydraulic oil, so the oil couldn't flow.

Safety is paramount

As you can see, pressure intensification in a double-acting hydraulic cylinder is a dangerous phenomenon and the concept must be thoroughly understood when testing hydraulic cylinders.

Related articles:

How to test hydraulic cylinders
A popular myth about hydraulic cylinders - exploded!
How to reduce hydraulic cylinder repair costs

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