On many industrial installations with a maximum pressure of about 200 bar, vane pumps are applied. This type of pump is also available with a variable displacement.
The shaft of the rotor with the radial mounted vanes is driven by an engine or motor. The stator ring is circular in form and is held in an eccentric position. The amount of eccentricity determines the displacement of the pump. By steering the stator ring towards the rotor (by hydraulic pressure, working on a piston) the amount of eccentricity and thus the displacement of the pump is decreased. At an eccentricity of zero, the displacement of the pump becomes 0 cm3: from that moment on the pump doesn't deliver any oil.