If hydraulic oil is pressurised, then its volume decreases. That means that, in the case of a rise in pressure Δp (delta p), the power source must provide an additional volume Vβ.
The volume Vβ is calculated from the compressibility factor β of the hydraulic fluid.
Compressibility volume
For hydraulic oil, β amounts to approx. 70 * 10-6 1/bar.
This means:
For a pressure increase of 100 bar, 0.7 % more oil volume is required.
In calculating Vβ of a hydraulic system, the total oil volume Vgeswhich is compressed must be taken into account. That means that all oil volumes must be added, from the pressure source hrough to the hydraulic cylinders.
Total Volume
Important!
Air in the hydraulic oil increases the compressibility and the additional volume Vβ. This causes a considerable increase in the actual stroke time tHt. That is why each hydraulic system must be bled carefully during start-up.
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