Abstract: A back flow prevention device is shown for use in a plastic pipeline for conveying water, sewage, hydrocarbons or other fluids. A valve body features a flow control mechanism which is formed entirely or primarily of plastic materials. The valve body and its opposing ends are formed of a plastic material which is compatible with the plastic material of the existing pipeline, whereby the valve body can be installed in the pipeline in co-axially fashion by directly joining the opposing ends of the body to the opposing mating pipe ends at a selected location within the pipeline.