PURPOSE: To dispense with a valve stem packing seal to be worn by providing a cylindrical insert made of corrosion-resisting plastic or food grade type elastomer in a pressure support metal housing surrounded by a pipe acting as a valve stem seal and a valve closing member at the same time.

CONSTITUTION: A valve housing 4 has a pair of flanges 7, and a bore 8 includes a cylindrical insert 9 surrounded by a tubular seal 10. The cylindrical insert 9 has a flattened portion 14 captured by a clearance gap 15 and permits the tubular seal 10 to be displaced with a certain eccentricity to the central horizontal axis. The cylindrical insert 9 forces a fluid to be communicated with a space provided between the flattened portion 14 and the inside diameter of the sleeve 10 through a number of vertical holes 19. A plunger 20 is adapted to displace the outer peripheral portion by the tubular seal sleeve 10 to cover an orifice 17, thereby interrupting fluid flow.