The device has a sealing member (14) occupying a liquid discharge position and a liquid blocking position. The member has an elastomer part (34) and a rigid part (36) connected with each other during movement. The elastomer and rigid parts are assembled by molding, welding, gluing or riveting. A return element (15) e.g. spiral metallic spring, exerts return force on the elastomer part to permit the part to reach the blocking position. The return element is supported against or fixed to the rigid part of the sealing member.
