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We’ve discussed the dangers of pressure intensification in a double-acting hydraulic cylinder. Now we’ll explain the use of intensification effect while testing the integrity of the piston seal for such cylinders. But before getting into this test procedure, it is strongly advised that the danger associated with the procedure is completely understood as described above.
The conventional testing carried out to check the integrity of a double-acting cylinder piston seal is to pressurize it at the end of the stroke to measure if any leakage gets past the seal. This is commonly known as the “end-of-stroke bypass test”.
However, the end-of-stroke bypass test has limitations, and the major one is that it doesn’t usually expose ballooning of the cylinder tube originated due to hoop stress. To test this, the ideal way would be to conduct a piston-seal bypass test at the mid-stroke. So the difficulty that comes along this test is that the force created by the cylinder is supposed to be mechanically resisted, but that is not practical for high-pressure cylinders with a larger diameter. However, conducting a mid-stroke bypass test hydrostatically can be done by using the intensification effect.
The test procedure is as follows:
- Secure the hydraulic cylinder with the service ports up.
- Both sides of the cylinder should be filled with the hydraulic fluid through the service ports.
- Follow the right procedure to connect ball valves, gauges, relief valve, and directional control valve.
- With ball valves open, stroke the hydraulic cylinder with the directional control valve a few times to extinguish all remaining air from the cylinder – but do not ‘diesel’ the cylinder.
- Correctly position the piston rod at mid-stroke and close the ball valve.
- Having adjusted the relief valve to back out, the direct flow will be made to the cylinder’s rod side.
- Start increasing the setting of the relief valve until the rated pressure is displayed on the gauge.
- Close the ball valve and center the directional control valve. Keep in mind that the hydraulic power unit used in the test has a protection for over-pressure.
- Keep records of the respective pressure gauge readings and monitor the change over time.
For an effective area ratio of 2:1 between the piston and the rod side of the cylinder, a 3,000 PSI pressure on the rod side will give a reading of 1,500 PSI on the piston side. To avoid any problem with the piston seal or tube, the differential pressure should be maintained across the piston.
Never, direct the flow to the cylinder piston side with the ball valve closed. Else, it will end up in the failure of the cylinder and an injury could result as well. Always use the required personal protective equipment while carrying out this test or any other hydrostatic test.
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