How to Test A Hydraulic Cylinder

Here at Motus Hydraulics, we have many products on offer including hydraulic cylinders or spring ram. In addition to assisting our customers with their purchase, we feel that it’s important to also help troubleshoot any issues they might have following their purchase. You might be wondering; how do you test a hydraulic cylinder?

There are a few different ways that you can test the integrity of the piston seal in a cylinder. Commonly known as the “end-of-stroke bypass test”, this method pressurises the cylinder at the end of the stroke to measure any leakage past the seal. However, one major limitation of this test is that it often doesn’t show ballooning of the cylinder tube caused by hoop stress. A way to counteract this is by using the intensification effect to test the integrity of the piston seal in the double-acting hydraulic cylinder. However, the dangers of this procedure should be fully understood before the test is carried out, and you can find out more about this here.

The ideal test conditions to check the ballooning of the cylinder is to carry out a piston-seal bypass test, mid-stroke. This is harder to do with high-pressure, large-diameter cylinders and deemed impractical, in part due to the force that’s developed by the cylinder as it has to be mechanically resisted. Having said that, there is a way to conduct a mid-stroke bypass test hydrostatically by using the intensification effect, which we’ll run through below. You can refer to the image for the necessary hydraulic cylinder test circuit for the numbers in the procedure.

Test Procedure

Figure 1. Hydraulic cylinder test circuit. Image credit: Hydraulics & Pneumatics.

  1. Secure the hydraulic cylinder with its service ports up.
  2. Fill both sides of the cylinder with clean hydraulic fluid via the service ports.
  3. Connect the ball valves (1) and (2), gauges (3) and (4), relief valve (5), and directional control valve (6) as shown in Figure 1.
  4. With ball valves (1) and (2) open, stroke the cylinder multiple times using the directional control valve (6) to remove all remaining air from both sides of the cylinder. Be careful not to “diesel” the cylinder.
  5. Position the piston rod in mid-stroke and close the ball valve.
  6. Direct flow to the rod side of the cylinder as the adjustment on the relief valve (5) will be backed out.
  7. Increase the setting of the relief valve (5) until the cylinder’s rated pressure is seen on the gauge (3).
  8. Close ball valve (1) and centre directional control valve (6). Note: it is assumed that the hydraulic power unit used to conduct the test will have its own over-pressure protection, which is not illustrated in Figure 1.
  9. Record the respective pressure readings on gauges (3) and (4) and monitor any change over time.

If the ratio of the effective area between the piston and rod side of the cylinder is 2:1, then if the rod side of the cylinder has been pressurised to 3,000 PSI, gauge (2) on the piston side should read 1,500 PSI. You’ll notice that there is a problem with the piston seal or tube if the differential pressure across the piston isn’t being maintained.

Flow should never be directed to the piston side of the cylinder if the ball valve (1) is closed. There is a risk of the cylinder failing, which could also potentially result in personal injury. It is advised that you always wear personal protection equipment (PPE) when carrying out any tests such as this.

IMPORTANT: Failing to consider the implications of pressure intensification in a double-acting hydraulic cylinder can be a costly mistake, so it’s important to bear that in mind as it is a potentially dangerous phenomenon.

Text has been adapted from this article by Hydraulics & Pneumatics.



Seth – AU Sales

Hartley Currie – General Manager