Abstract: A backflow prevention apparatus of light weight, modular construction which provides quick and easy access to internal check valves. The backflow prevention apparatus generally comprises a tubular valve body having a lateral opening, at least one check valve positioned within the flow stream of the tubular valve body, a movable sleeve which fits over the valve body and is configured to cover the lateral opening in the valve body, and seals, associated with the sleeve valve body, for providing a fluid tight seal between the sleeve and valve body. The tubular valve body has openings at first and second ends, and the lateral opening is flangeless. Preferably, the backflow preventer includes a first, upstream check valve and a second, downstream check valve each having thereon a stop or ridge thereon.