In a previous article, I described the danger associated with the intensification of pressure in a double-acting hydraulic cylinder. In this article, I will explain how to use the intensification effect to test the integrity of the piston seal in a double-acting 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 as a result of under-designed cylinder wall thickness or reduction of wall thickness through excessive honing. 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.
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 (2) 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.
Safety is paramount
Under no circumstances should flow be directed to the piston side of the cylinder with ball valve (1) closed. 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.
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