Abstract: A control valve comprises a valve housing (1) having an inlet side (17) and an outlet side (18). The control valve also has a pressure maintaining arrangement for maintaining a constant differential pressure between the inlet and outlet sides, as well as an amount control arrangement for setting the maximum flow through the valve. A pair of cylinder shells located in the flow path have cooperating recesses which provide an uncovered area forming an opening (25). One cylinder shell is rotatable relative to the other cylinder shell by a rotatable handle (13), whereby a larger or smaller opening (25) between the cooperating cylinder shells may be provided. Both cylinder shells are axially displaceable within a seat hole (8), resulting in an increase or a decrease of the opening (25).