Drain with check valve

Claim 1

A drain comprising: a vertical hollow pipe; a bouyant spherical ball located inside the pipe and having a diameter less than the inside diameter of the pipe so as to be free to move up and down inside it; an upper stop in the top of the pipe for limiting the upward movement of the ball and preventing the influx and efflux of water into and from the pipe when the upward movement of the ball has been physically checked by the upper stop, the upper stop taking the form of a plug threaded into the top of the pipe, the plug bearing a cylindrical cavity smaller in diameter than the diameter of the ball extending through it concentrically with the inside of the pipe and bearing two opposed tabs extending radially outwardly from its center on its upper surface; and a lower stop in the pipe below the upper stop for limiting the downward motion of the ball while allowing water to flow upwardly or downwardly past the lower stop and preventing the air pressure head from raising the ball and thus closing the drain before the arrival of flood water, the lower stop taking the form of a U-shaped member welded into the pipe with the open side of the U facing upwardly and extending a substantial distance across the pipe so as to contact the pipe at four separated locations.