Overflow valve

An overflow valve (100, 200) for limiting the pressure in a system in which a liquid is lifted by a positive-displacement pump and flows through the system with varying rates of flow, comprising a valve chamber (1) with an inlet opening bordered by a valve seat (3) for the entry of liquid into the valve chamber (1) and with at least one outlet opening (5) in connection with the runback to the positive-displacement pump for the outlet of the liquid out of the valve chamber (1), as well as a valve body (22) placed displaceable inside the valve chamber (1) with a valve head (14), whereby the valve body (22) is pressed with a valve body (14) by a first spring (21) sealing against the valve seat (3) and is lifted off from the valve seat (3) at an opening pressure of the liquid determined by a first active diameter of the valve head (14) against the force of the first spring (21) and opens the inlet opening (2), wherein

• that the valve chamber (1) with an extension (4) turned to the inlet opening (2) on the delivery side and enlarging in direction of the spring (21) and the valve body (22) with the valve head (14) placed in the valve chamber are constituted so that the valve head, after lifting off from the valve seat (3), has a second active diameter with a preceding retaining room, the second active diameter being bigger than the first active diameter, and whereby the valve head (11) simultaneously releases, with increasing stroke of the valve body (22), an enlarging flowing-through cross section, that the valve body (22) is constituted in one part as a valve piston (11) sliding in the valve chamber (1) with a third active diameter with a preceding retaining room, the third active diameter being bigger than the second active diameter, and that the liquid flowing through the valve chamber (1), the valve being opened, produces a pressure difference which acts onto the valve piston (11) against the action of the first spring (21).