In a previous post, I described the danger associated with the intensification of pressure in a double-acting hydraulic cylinder. In this post, I will explain how to use the intensification effect to test the integrity of the piston seal in a double-acting hydraulic cylinder. But before attempting this test procedure, it is absolutely essential that the danger associated with pressure intensification in a hydraulic cylinder is fully understood. Therefore, read this article FIRST!
The conventional way of testing the integrity of the piston seal in a double-acting cylinder is to pressurize the cylinder at the end of stroke and measure any leakage past the seal. This is commonly referred to as the “end-of-stroke bypass test”.
The major limitation of the end-of-stroke bypass test, is that it generally doesn’t reveal ballooning of the cylinder tube caused by hoop stress. The ideal way to test for ballooning of the cylinder tube is to conduct a piston-seal bypass test, mid-stroke. The major difficulty with doing this is that the force developed by the cylinder has to be mechanically resisted, which in the case of large diameter, high-pressure cylinders is impractical.
However a mid-stroke bypass test can be conducted hydrostatically using the intensification effect. The necessary circuit is shown in Figure 1 below.
Figure 1. Hydraulic cylinder test circuit.
Test procedure
The procedure for conducting the test is as follows:
If the ratio of effective area between the piston and rod side of the cylinder is 2:1, then if the rod side of the cylinder has been pressurized to 3,000 PSI, gauge (4) on the piston side should read 1,500 PSI. If the differential pressure across the piston is not maintained, this indicates a problem with the piston seal or tube.
Under no circumstances should flow be directed to the piston side of the cylinder with ball valve (1) closed. This will result in potentially dangerous pressure intensification, and failure of the cylinder and/or personal injury could result. When conducting this or any other hydrostatic (pressure) test, always wear appropriate personal-protection equipment.
For more on testing and troubleshooting hydraulic cylinders, read chapter 13 of The Hydraulic Troubleshooting Handbook
Brendan, Thanks for a wonderful follow up article. You included a lot of really good and detailed information. Because it can be so dangerous I would say that each person testing the hydraulic cylinders should know their system inside and out before starting any testing. I look forward to your next article!
Tim on 4 January 2017 at 6:56 am said:Brendan, Thanks for this and all of your other articles on hydraulic systems. I keep them for reference and to pass on to others. It must be my nagging attention to detail but in this article when you discuss the ratio of 2:1 you refer to gauge (2) when I think you mean (4). I don’t want to come across as critical just wanted to let you know. If I am miss reading this then please let me know. Thanks again
