Abstract: A control for use by a patient who is connected with a respirator comprises a valve housing which has an interior valve chamber with a gas inlet extending into the chamber and terminating at an annular valve seat which is closable by a diaphragm. A gas outlet is also connected into the valve chamber. The valve housing also has a control chamber in the opposite side of the diaphragm from the valve chamber and an inhaling gas supply connection extends into the control chamber. In addition a gas take-off conduit connectable to the patient is connected into the control chamber. The gas take-off is provided with an orifice plate which defines a reduced area in the take-off so that during use by the patient during inhaling a pressure lower or higher than the pressure in the valve chamber is produced in the control chamber and opening or closing of the diaphragm end valve is effected to permit or prevent exhaled gas to pass through the gas inlet connection to the valve chamber and then to the gas outlet.