Flush valve improvements for controlling flushing volume

A flush valve includes a body with an inlet and an outlet and a valve seat at the outlet. There is a valve movable in the body toward and away from the valve seat to control flow through the flush valve. There is a chamber in the body above the valve and there is a refill orifice in the valve connecting the chamber with said body inlet. Pressure in the chamber maintains the valve closed upon its valve seat, with the size of the refill orifice controlling the time to fill the chamber from the inlet which determines the time of flow of water from the inlet through the outlet. There is a relief valve for venting the chamber to the outlet when the relief valve is open, thereby causing the valve to move away from its seat permitting flow from the inlet through the outlet. There is a cover threadedly attached to the body and a seal element formed from an elastomeric material positioned between the cover and the body. The seal element has a surface finish with sufficient lubricity such that the cover will slide upon its surface when the cover is threadedly attached to the body. The seal element is sufficiently elastomeric such that it distorts under pressure from the cover to form a tight seal between the cover and the body.