The invention relates to an actuator (10) for controlling a fluid flow which comprises a valve housing (11), a flow restrictor (18) and a valve seat (16), in which the flow restrictor (18) is designed such that the flow restrictor (18)—together with a closure (22) which is connected to the valve housing (12)—will form a pressure-relieving chamber (28), and as a result, a relative movement of the flow restrictor (18) and the chamber closure (22) together with the actuation will cause the volume of the pressure-relieving chamber (28) to change as a function of the direction of movement, and the flow restrictor (18) has a recess (24) which will allow the fluid to be controlled to flow into the pressure-relieving chamber (28). The invention is characterized in that the seal (26, 30) between the flow restrictor (18) and the valve housing (11) is designed such that, in the closing position, with the flow restrictor (18) resting tightly on the valve seat (16), the seal (26, 30) will have a sealing effect, and with the flow restrictor (18) not resting on the seat, the seal (26, 30) will allow a defined amount of fluid from the pressure-relieving chamber (28) to pass through.