One-sentence answer: A hydraulic cylinder maintains pressure through the threaded or welded connection between the cylinder barrel and the cylinder head, as well as the piston rod seal. Internal leakage prevents the cylinder from holding pressure, while external leakage pollutes the environment. Using the CTS Sentinel A28 differential pressure leak detector to compare a master part with the part under test can offset the effects of temperature drift on medium-to-large-volume cylinder cavities, making it suitable for 100% inspection on batch production lines for small and medium-sized cylinders.
The volume of both cylinder chambers rises rapidly with bore diameter and stroke, so the testing time per part is much longer than for small parts. If the judgment method relies on absolute pressure stability, the cycle time becomes unacceptable.
For the same cylinder, the volume difference between the two chambers is significant when the piston stops at mid-stroke versus at the end of the stroke. If the fixture does not fix the piston position, the judgment limit loses consistency.
The threaded connection between the cylinder barrel and the cylinder head relies on sealing rings or end-face contact, while welded cylinder barrels depend on weld quality. The upper pressure limits for detecting these two types of defects differ.
The larger the volume, the more pronounced the gas pressure drift under the same temperature difference. Day-night temperature variations in the workshop or residual heat from the workpiece can make single-channel direct pressure readings lose comparability.
Sealing locations:
Consequences of leakage: Internal leakage causes the cylinder to fail to hold pressure, resulting in slow boom descent and positioning drift of the actuator. External leakage causes hydraulic oil seepage, which wastes oil, pollutes the site, and may cause safety accidents due to insufficient pressure.
Small and medium-sized cylinders are medium-to-large-volume, batch-produced workpieces, and the judgment difficulty lies precisely in the effect of temperature on pressure:
If the cylinder specifications exceed the common range for single-channel small parts, or if multiple test methods need to be connected in series at the same station, a comparative evaluation with the I28 multi-function single-station model can be conducted based on the specific working conditions.
It will be longer than for small parts because charging and stabilization need to fill the entire cavity. There are three directions for optimization: select an air source with appropriate flow and pressure, calibrate the stabilization time in the test program based on actual measurements rather than using a conservative value, and use differential pressure comparison to shorten the wait for absolute pressure stabilization. The specific time needs to be measured according to bore diameter and stroke.
Because the volume of both chambers changes with piston position, and the pressure response of the same cylinder is completely different at different positions. If the fixture does not constrain the piston, the judgment limits have no consistency, and the previous part passing does not mean the next part is judged under the same conditions. Writing piston positioning into the fixture design is a prerequisite for ensuring repeatable testing.
A pressure test verifies structural strength, using water or oil at higher pressure to confirm that the housing and welds do not crack. An air tightness test verifies sealing performance, using gas at lower pressure to determine whether leakage occurs. The two have different purposes. Typically, an air tightness test is performed first to screen out parts with poor sealing, and then pressure verification is performed on a specified proportion or on all parts.
The key to sealing tests for hydraulic cylinders is maintaining consistent judgment under conditions of large volume and temperature fluctuation. The differential pressure comparison structure of the CTS Sentinel A28 directly addresses this point. Combined with a plugging fixture that can position the piston and 32 test programs, it meets the 100% inspection requirements of batch production lines for small and medium-sized cylinders.
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