The valve has an actuation lever (5) for opening a main valve against a biasing force of the main valve. A valve actuator exhibits a continuous curve with a stepless gradient. An opening force is exerted on the main valve using the stepless gradient at beginning of a valve opening stroke when the actuation lever is pressurized with an operating force lesser than another operating force in a gradient of the valve opening stroke. The actuation lever and the valve actuator of the main valve are kinematically connected with each other over a coupled gear.
