Abstract: A valve assembly which includes a valve body made of a hard synthetic resin, preferably PVC or PVDF. The valve body is formed with a fluid passage laterally extending therethrough, and having no flanges for connection with neighboring pipings. There is a valve member for the cooperation with the valve body, the valve member has nearly a true cylindrical outer configuration, having a taper of 1/30-1/10. A shallow concave groove or recess is formed in the bottom wall surface of the valve member kept in fluid communication with the axial bore formed in the latter. The material of the valve member is selected to be softer than that of the valve body for securing benefit for aquiring better wearing characteristics in cooperation with the valve seats. This material is preferably polypropylene. The working surface of the valve member has a generally convex-cured configuration and the valve seat of the valve body has a concave configuration mating therewith.