The ball valve has a housing (2) with two pipe fittings (2.1,2.2) and enclosing a ball valve (1) and a stopcock (3) by means of which the valve is opened and closed. The tap has a metal ring seal (5) between the housing and ball. The ring seal has coaxial shoulder (5.1) embedded in the housing. The shoulder has a radial inner surface (5.3) which rests against the housing surface. The coefficient of the metal ring seal is the same as or is greater than that of the ball valve. The surface of the ring seal touching the ball conforms to that of the ball. The ring seal coaxial shoulder is surrounded by a groove (5.5) between it and the main body of the ring seal. The seal inner surface over which fluid flows is inclined outwards around the ball at an angle of up to 20 deg .
