Piston valve for opening and closing the flow path of a fluid between an inlet and an outlet , the piston valve comprising a hollow housing having an inner cavity and a longitudinal axis , an inlet provided in the housing , an outlet communicating with the inlet only through the piston valve and a pushbutton that can be moved in and out direction compared to the housing wherein the pushed in and pulled out states of the pushbutton set the closed respectively open states of the piston valve , wherein the piston valve comprises furthermore a valve piston with two opposite end faces and arranged in the hollow interior of the housing and guided for displacement along said longitudinal axis , a valve seat provided on an element extending normal to said longitudinal axis , wherein in an extreme position of the valve piston when it is pressed to the valve seat the piston valve is in closed state, and the inlet is led through a passage into the inner cavity of the housing so that in the closed state of the valve piston a lower portion of the valve piston closes said passage , wherein a control valve is arranged in the inner cavity of the hollow housing in a predetermined axial distance from the valve seat and the opening and closing of the control valve is controlled by the position of the pushbutton , and in the interior of the housing between the valve piston and the control valve an intermediate space is formed and the size of the intermediate space depends on the momentary position of the valve piston , and a shunt flow passage is provided between the two end faces of the valve piston providing a small fluid flow, wherein the cross section of the shunt passage is smaller than the flow cross section of said control valve when being in open state, and above the control valve the inner cavity of the housing defines an upper space between the control valve and the pushbutton , a spring is arranged in the upper space that presses the control valve to its closing direction, and the housing comprises a passage that interconnects the interior space under the valve seat with said upper space , and between the pushbutton and the valve piston there is no mechanical connection, and the pushbutton controls the valve piston only by utilizing the established fluid flow and the associated pressure patterns, characterized in that in said intermediate space a further spring is arranged that presses the valve piston to take a closed position and in that : - a radial groove is provided on the outer surface of the valve piston and a ring made of a resilient material is inserted in the groove , wherein the width and/or depth of the groove is greater than the size of the ring and the so resulting gap constitutes said shunt passage or at least a portion thereof, and/or - along the outer mantle of the valve piston at least one axial cut is provided and this constitutes said shunt passage or at least a portion thereof. - a radial groove is provided on the outer surface of the valve piston and a ring made of a resilient material is inserted in the groove , wherein the width and/or depth of the groove is greater than the size of the ring and the so resulting gap constitutes said shunt passage or at least a portion thereof, and/or - along the outer mantle of the valve piston at least one axial cut is provided and this constitutes said shunt passage or at least a portion thereof. <EOS>