A control valve having an outlet and being configured to connect the outlet to a low pressure source or to a high pressure source, the control valve comprising an outlet chamber connected to the outlet, a high pressure port to the outlet chamber, a low pressure port to the outlet chamber, a valve disk movable between a first position closing the high pressure port and a second position closing the low pressure port, a pilot circuit, which acts on a membrane acting mechanically on the valve disk via a flexible portion of the membrane, an actuator configured to connect the pilot circuit to one of the low pressure source and the high pressure source, wherein the membrane is configured to move the valve disk to the first position when the pilot circuit is connected to the high pressure source and to move the valve disk to the second position when the pilot circuit is connected to the low pressure source, wherein the membrane extends along an extension plane (p), a central axis (x) of the membrane is perpendicular to the extension plane (p), the membrane comprises an outer annular rim portion, a central portion configured to be connected to the valve disk, and the flexible portion that is annular and provided between the central portion and the outer annular rim portion, and the membrane is flexible to permit the central portion to move back and forth along the central axis (x), thereby permitting the valve disk to move to one of the first position and the second position, characterized in that the membrane is designed with an inherent pre-tensioning of the flexible portion, which permits the membrane to exert a force on the valve disk from the first position towards the second position, wherein the flexible portion has a wavy shape with a circular wave peak and a circular wave valley, wherein the wave peak is located more closely to the central axis (x) than the wave valley, wherein the membrane has an active side and a passive side, wherein the outer annular rim portion has an annular surface on the active side, and the wave peak is located above the annular surface in a rest position of the membrane. a high pressure port to the outlet chamber, a low pressure port to the outlet chamber, a valve disk movable between a first position closing the high pressure port and a second position closing the low pressure port, a pilot circuit, which acts on a membrane acting mechanically on the valve disk via a flexible portion of the membrane, an actuator configured to connect the pilot circuit to one of the low pressure source and the high pressure source, wherein the membrane is configured to move the valve disk to the first position when the pilot circuit is connected to the high pressure source and to move the valve disk to the second position when the pilot circuit is connected to the low pressure source, wherein the membrane extends along an extension plane (p), a central axis (x) of the membrane is perpendicular to the extension plane (p), the membrane comprises an outer annular rim portion, a central portion configured to be connected to the valve disk, and the flexible portion that is annular and provided between the central portion and the outer annular rim portion, and the membrane is flexible to permit the central portion to move back and forth along the central axis (x), thereby permitting the valve disk to move to one of the first position and the second position, characterized in that the membrane is designed with an inherent pre-tensioning of the flexible portion, which permits the membrane to exert a force on the valve disk from the first position towards the second position, wherein the flexible portion has a wavy shape with a circular wave peak and a circular wave valley, wherein the wave peak is located more closely to the central axis (x) than the wave valley, wherein the membrane has an active side and a passive side, wherein the outer annular rim portion has an annular surface on the active side, and the wave peak is located above the annular surface in a rest position of the membrane.