Hydraulic capacity is a measure of the volume accommodated based on the pressure increase required. It is a function of the compressibility of the fluid. The compressibility of the oil in a pipe is increased by the elasticity of the walls and any undissolved air in the oil. The equivalent bulk modulus K’ (bulk modulus) concerns these characteristics in respect of a pipe filled with oil. If the enclosed oil volume under pressure is represented by the letter V, the pipe capacity may be calculated as follows.
The dynamic performance of hydraulic drives is largely dependent on the pipe capacity. The greater the pipe capacity, the worse the dynamic performance (Figure L 18) of the hydraulic drive, since its hydraulic natural frequency is reduced.