Hydraulic machines (pumps, motors) in which hydrostatic power is transferred downstream of the Positive displacement principle.
In terms of the operating principle, a distinction is made between circumferential displacement machines and piston machines.
In the circumferential displacement machines the transport process takes place in a circumferential direction and is characterised by the size 2π. The displacement units are gear wheels and moving or rigid barrier elements (vanes).
The group of piston machines works according to the reciprocation principle, with the displacement units (generally pistons) performing a linear movement.
All displacement machines – with the exception of the screw pumps – can be classified using the aforementioned schematic.
Opposite: flow machines.