Hydraulic jack or cylinder calibration

Checking a pressure gauge on a pressure test bench tells you something about the gauge, but not about the force the jack delivers. The force is the pressure multiplied by the effective piston area, minus the friction in the seals. That friction varies from cylinder to cylinder, from stroke to stroke and from direction to direction. That is why we calibrate the jack with its pressure gauge or display as a single unit:

• the jack presses against a calibrated reference force transducer in our compression test bench;
• at each load step we record the reading of your pressure gauge or display and the force measured by the reference;
• this produces a table or correction with which you convert the reading into the actual force.

We recommend calibrating the jack with the pump, hoses and pressure gauge you use on site. State in your request whether you want the extension (stroke) to be taken into account; the position of the piston can affect the result.

• Deliver the jack clean and free of leaks, stating the effective piston area if known.
• We collect heavy jacks with our own transport and return them; the calibration takes place on our compression test bench at our Elspeet facility.
• If the pressure gauge is defective or unreadable, we let you know before proceeding.
• You receive the measurement results in kN, t or in the unit of your pressure gauge, with the measurement uncertainty according to EURAMET cg-4.

The certificate shows, for each measuring point, the reading of your pressure gauge or display alongside the actual force. You can work with this in two ways:

• Correction table. You read the pressure gauge and look up the corresponding force in the table. Between two measuring points you interpolate linearly.
• Conversion formula. On request we provide a linear or quadratic equation that converts the reading into force. Useful if you want to include the conversion in a spreadsheet or measurement program.

An example: if the pressure gauge reads 350 bar during prestressing and the table gives 1,480 kN at that pressure, then that is the force your jack has delivered, within the stated measurement uncertainty.

In construction and civil engineering, the force of a jack is often recorded as evidence that a structure has been built correctly. In prestressing anchors and cables, the jack force determines the stress in the steel. In a static load test of a pile or foundation, the measured force is the basis for assessing the bearing capacity. In jacking bridges and buildings, a reliable force measurement prevents a structure from being loaded unevenly.

In all these cases the client usually requires a valid calibration certificate for the jack with its readout, sometimes with a maximum age. Plan the calibration well before the start of the project.

Select the measuring range: the maximum force you want to have calibrated. We calibrate jacks and cylinders in compression.