Adjusting valve for adjusting the delivery volume of a displacement pump

An adjusting valve for adjusting the delivery volume of a displacement pump, said adjusting valve comprising:

• a) a valve casing;
• b) a hollow valve piston mounted such that the hollow valve piston can be moved within the valve casing, thereby forming two active surfaces for a valve-actuating pressure of a fluid, wherein the valve casing comprises a surrounding surface, which surrounds the hollow valve piston and has a port;
• c) a valve spring which counteracts a force exerted by the valve-actuating pressure on the hollow valve piston;
• and
• d) an adjusting device, wherein the hollow valve piston is adjustable by the adjusting device in the direction of or counter to the force exerted by the valve-actuating pressure,
• e) wherein the two active surfaces are arranged to counteract each other and are of different sizes in order to generate a differential force which acts on the hollow valve piston counter to the valve spring and corresponds to a difference in the size of the two active surfaces, and
• f) wherein the two active surfaces limit the same fluid space and face each other in the direction of the mobility of the hollow valve piston such that the fluid space is located between the two active surfaces,
• g) wherein the hollow valve piston comprises a cylindrical surface region, which is adjacent to one of the two active surfaces in the direction to the adjusting device and together with said surrounding surface of the valve casing forms a narrow sealing gap which fluidically separates the adjusting device from the fluid space, wherein an aperture is formed in said cylindrical surface region of the hollow valve piston, wherein the hollow valve piston is movable from a position in which said aperture is sealed by the surrounding surface into a position in which said aperture is in flow communication with said port.