Hydraulic Cylinders and Pressure Intensification

hydraulic cylinder failureA question 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 post I will explain the dangers of intensification in a double-acting cylinder and in my next post I will explain the test procedure.

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.

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.

As you can see, pressure intensification in a double-acting hydraulic cylinder is a potentially dangerous phenomenon. And failing to consider its implications can be a costly mistake. To discover six other costly mistakes you want to be sure to avoid with your hydraulic equipment, get “Six Costly Mistakes Most Hydraulics Users Make… And How You Can Avoid Them!” available for FREE download here.

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