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, assembly and testing are all performed in-house on the 20,000 m² site in Turkiye, Konya, so test results feed directly back into production.
ISO 10100 and the Test Pressure
ISO 10100 defines the acceptance test for hydraulic fluid power cylinders. At HPS, test pressure follows the drawing, otherwise 1.5 × nominal pressure under this standard. HPS cylinders have a nominal pressure of 250 bar as standard, with higher pressures to drawing. 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.
Test Bench Procedure, Step by Step
The tests run on the test bench. In the function test the cylinder is extended and retracted, and it must make a full stroke at low pressure with no sticking or irregular movement. The pressure test applies the test pressure on the drawing, otherwise 1.5 × nominal pressure (ISO 10100), with no visible permanent deformation allowed. In the internal leakage test, double-acting cylinders must show no internal leakage with the opposite port open, where applicable. The external leakage test checks ports, seals and welds for oil, and no external leakage is allowed. Final inspection confirms lengths, mounting dimensions and port positions against the approved drawing. 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, internal leakage is checked with the opposite port open: in double-acting cylinders, where applicable, no fluid may come from that port. The acceptance criterion for external leakage is just as clear: no oil at ports, seals or welds. 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 Report and EN 10204 3.1
A pressure test report is issued on request for every accepted cylinder. EN 10204 3.1 material certificates are available on request for pressure-carrying components such as the tube and rod. Typical documented materials are EN 10305-1 E355 tube and CK45 or 42CrMo4 rod. HPS exports to 49 countries under HS code 8412.21, with EXW, FCA, CIP, CIF and DAP Incoterms; the certificates travel with the commercial documentation.
Rod Plating and Bore Tolerance
Pressure testing is the final gate, but rod plating and bore tolerance determine long-term sealing performance. The piston rod is C45E (Ck45) or 42CrMo4, hard-chrome plated to min. 20 µm per side, typically 30 µm. The barrel is honed tube, EN 10305-1 E355, with a bore tolerance of H8 or H9 as agreed, which gives 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.
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