Butterfly valve

A valve comprising:

• a hollow cylindrical conduit having an axis;
• pivot means extending through said conduit and through the axis thereof;
• a butterfly valve including a disc fixed to said pivot means in a manner to rotate therewith, said butterfly valve disc having a peripheral surface of revolution about said axis when said butterfly valve is closed, said conduit having a cylindrical groove therein symmetrical with said surface of revolution when said butterfly valve is closed;
• and a ring of rectangular cross section in said groove to seal against said surface of revolution, said groove having annular side walls, said ring being split at one point around its periphery and having mating ends at said point, one of said ends having a notch, the other of said ends having a projection to fit in said notch, said notch being V-shaped and being defined between two flat surfaces lying in planes normal to said side walls and inclined relative to each other at a predetermined angle, said two flat inclined planes intersecting in a line normal to said side walls, said projection having two surfaces inclined at said predetermined angle to form a wedge shaped body having an edge in a line normal to said side walls to fit contiguous to the bottom of said notch.