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Hydraulic Cylinder Pressure Testing: The 1.5x Factory Acceptance Test

Every hydraulic cylinder that leaves the HPS plant in Konya, Türkiye is pressure-tested on a test bench before shipment. The acceptance test is run at 1.5 times the rated working pressure in accordance with ISO 10100. For a cylinder rated at 250 bar, that means a test pressure of 375 bar. This guide explains the test sequence, the pass criteria concept, and the documentation available to quality and procurement teams.

Why Factory Acceptance Testing Matters

A hydraulic cylinder is a pressure-containing component, and a defect that escapes the factory becomes a field failure. Factory acceptance testing verifies each individual cylinder, not just the design or a sample. It detects assembly errors, seal damage and porosity before the cylinder is installed in a machine. At HPS, machining, welding, honing, chrome plating, assembly and testing are all performed in-house at the 20,000 m2 plant in Konya/Karatay, so test results feed directly back into production. For buyers exporting equipment, a documented test is also the basis for traceable quality records.

ISO 10100 and the 1.5x Rated Pressure Rule

ISO 10100 defines the acceptance test for hydraulic fluid power cylinders. HPS tests every cylinder at 1.5 times its rated working pressure per this standard. HPS cylinders are rated for working pressures of 200 to 250 bar; at a 250 bar rating the test pressure is therefore 375 bar. The overpressure margin proves that the tube, welds, rod, and static and dynamic seals withstand loads above anything expected in normal service. System-level safety remains governed by ISO 4413, and fatigue behaviour is addressed separately under ISO 10771-1.

Test Bench Procedure, Step by Step

The test runs on a dedicated test bench in a fixed sequence. First, the cylinder is cycled over its full stroke to confirm smooth motion, correct stroke length and correct port function. Second, an internal leak check verifies that pressurized fluid does not bypass the piston from one chamber to the other. Third, an external leak check inspects the rod seal, port connections and welds for any visible leakage at test pressure. Finally, a drift (holding) check pressurizes the cylinder in a fixed position and monitors rod movement over time; measurable drift indicates internal bypass. Only cylinders that pass all steps are released for shipment.

What Internal Leakage Means: Piston Seal Bypass

Internal leakage is fluid passing from the high-pressure chamber to the low-pressure chamber across the piston seal, known as piston seal bypass. The cylinder can still move, so the defect is invisible from outside, but the load creeps under pressure and holding capability is lost. On the test bench it is detected as rod drift while the cylinder is held pressurized in a fixed position. The pass criteria concept is simple: drift and leakage must stay within the acceptance limits defined for the test before a cylinder is approved. Seal material also matters: HPS fits NBR as standard up to about 90 C, with HNBR, PU, FKM and PTFE options, and final seal selection is verified by engineering.

Documentation: Pressure Test Certificate and EN 10204 3.1

A pressure test certificate is issued on request for every accepted cylinder. For material traceability, EN 10204 3.1 material certificates are available on request for pressure-carrying components such as the tube and rod. Typical documented materials are DIN 2391-2 ST52 / EN 10305-1 E355 tube and CK45 or 42CrMo4 rod. These documents let quality departments link each cylinder to its test result and its material documentation. HPS exports to more than 35 countries under HS code 8412.21, with EXW, FCA, CIP, CIF and DAP Incoterms; the certificates travel with the commercial documentation.

Related Verification: NSS Salt-Spray and H8-H9 Honing Tolerance

Pressure testing is the final gate, but two upstream verifications determine long-term sealing performance. The piston rod is CK45 or 42CrMo4 with a hard-chrome layer of about 30 um, and the chrome surface is salt-spray (NSS) tested for corrosion resistance. The cylinder tube is honed to an H8-H9 tolerance, giving the bore the geometry and surface finish the piston seal needs to seal reliably. Rod coating quality and bore tolerance directly influence external leakage at the rod seal and internal bypass at the piston. Full technical parameters, including live force and buckling calculations, are available in the online configurator on the HPS website.

Calculate live in the configurator →Request a quote
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