There are several ways to test a hydraulic cylinder to determine its function, the one in this article being the simplest one. When you purchase high-quality hydraulic cylinders you will rarely experience problems, but sometimes components may arrive faulty or breakdown during use. This can be for a number of reasons, for instance:

• The cylinder was used outside of its intended tolerances
• The cylinder was poorly engineered or manufactured from a low grade material
• The cylinder developed a mechanical fault due to excessive use, e.g. a leak.

Sometimes a fault is obvious, but in other cases the cause of an issue may not be clear. Testing your hydraulic cylinders is a useful process of elimination to rule out a more serious fault – and can often be remedied simply by swapping out component seal. If in doubt, please consult a professional before testing a hydraulic cylinder or swapping a component. The cause of some mechanical failures are not obvious – simply exchanging components may compound the issue rather than making it better.

What Could Go Wrong?

The most common thing to go wrong in a hydraulic cylinder is the piston seal – especially so in double acting hydraulic cylinders. Piston seals are vulnerable to intense pressure and may develop leaks. Hoop stress is another common problem, which may cause ballooning in the cylinder barrel.

The End Of Stroke Bypass Test

The end of stroke bypass test involves pressurising a hydraulic cylinder in a test circuit and checking for leakage at the piston seal. Cylinder barrel ballooning can also be detected, although to do this the bypass test must be conducted mid stroke. Due to the forces involved, this may not be practical for high-pressure components.

Leaks are detected by measuring the differential between pressure at the cylinder rod side compared to that on the piston. The ideal rod to cylinder ratio is 2:1 for most units. If this is not the case then a leak is likely.

Here is a brief outline of how to conduct the test yourself:

• Open the cylinder’s service ports and secure them in the up position.
• Use the service ports to fill the cylinder with fresh hydraulic fluid.
• Create a hydraulic cylinder test circuit by connecting the ball valves, directional control valve and relief valve. Attach a pressure gauge to each end of the cylinder.
• Use the directional control valve to remove all air from both sides of the cylinder.
• Move the piston shaft into mid stroke position
• Apply pressure to the rod side, adjusting the relief valve settings until the pressure rating is displayed on the gauge
• Once pressurised, close the ball valve and centre the directional control valve. Be careful not to over pressurise the cylinder.
• Note down the pressure readings on the gauges at the rod and piston seal end. Compare these to the ideal 2:1 ratio already discussed.

If you conduct these tests regularly you can establish benchmarks for normal operating parameters and monitor changes over time. This makes leaks easier to detect at an early stage before the risk of a dangerous mechanical failure becomes high.

Deliberately pressurising a hydraulic cylinder in a test environment can be dangerous, especially if there is a mechanical fault. Only fully trained engineers should conduct these tests. Please contact us for help and advice.

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