Displacement refers to the pump (or motor) per revolution, by the sealing cavity geometry size changes in the discharge (or input) volume of the liquid, commonly used units are ML/R (ml/rpm).
Displacement can be adjusted to change the variable pump (or variable motor), the displacement cannot change into a quantitative pump (or quantitative motor). The actual flow is the flow of the pump (or motor) at the outlet (or inlet) at the point of operation. The actual flow is less than the theoretical flow due to the internal leakage of the pump itself. As the motor itself is also leaking, to achieve the specified speed, in order to compensate for leakage, its input actual flow must be greater than the theoretical flow.