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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 mate

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.

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1. A natural gas pipeline having a back flow prevention device installed therein, the natural gas pipeline being formed of polyethylene having a given external diameter and an interior, the back flow prevention device being formed primarily of plastic material compatible with the polyethylene pipeli

1. A natural gas pipeline having a back flow prevention device installed therein, the natural gas pipeline being formed of polyethylene having a given external diameter and an interior, the back flow prevention device being formed primarily of plastic material compatible with the polyethylene pipeline, the combination comprising:a check valve mechanism press-fit within the interior of a surrounding body making up a portion of pipeline and seated against a pre-existing register provided within the interior of the pipeline, the check valve mechanism allowing flow of fluids in a first direction and preventing the flow of fluids in a second, opposite direction; wherein the surrounding body has opposing ends formed of a plastic material which is compatible with the polyethylene of the pipeline, and wherein the surrounding body has an external diameter which is substantially equal to that of the remainder of the pipeline, whereby the surrounding body can be installed in the pipeline in co-axial fashion by directly joining and fusing the opposing ends thereof to opposing mating pipe ends at a selected location within the pipeline. 2. The device of claim 1, wherein the valve body is formed of polyethylene.3. A natural gas pipeline having a back flow prevention device installed therein, the natural gas pipeline being formed of polyethylene having a given external diameter, the combination comprising:a valve body formed of polyethylene, the valve body having an exterior defined between opposing ends and associated end openings, the valve body also having an initially open, cylindrical interior; a check valve mechanism located within the interior of the valve body and moveable between a first position which allows flow of fluids in a first direction and a second position which prevents the flow of fluids in a second, opposite direction, the check valve mechanism including a cylindrical mounting portion formed of polyethylene, thereby giving the mounting portion expansion and contraction characteristics indentical to those of the surrounding valve body, the cylindrical mounting portion having a cylindrical exterior of a diameter which can be slidably received within the initially open, cylindrical interior of the valve body and which is sized to be press-fit within the cylindrical interior of the valve body; wherein the check valve mechanism also includes a movable plate element having a contoured rear surface which engages and seals against a seat region of the cylindrical mounting portion of the check valve mechanism to control the flow of fluid through the pipeline, the contoured rear surface of the plate element being geometrically truncated such that at low pressure, seal contact area is proportionately reduced, thereby producing a contact seal with a high interfacial pressure; wherein the valve body with its opposing ends formed of polyethylene is compatible with the polyethylene of the pipeline, and wherein the valve body has an external diameter which is substantially equal to that of the remainder of the pipeline, whereby the valve body can be installed in the pipeline in co-axial fashion by directly joining and fusing the opposing ends thereof to opposing mating pipe ends at a selected location within the pipeline. 4. A method of installing a back flow prevention device within a hydrocarbon conveying, polyethylene pipeline having a given diameter, the pipeline being formed of pipe sections having a exterior and a generally cylindrical interior, the method comprising the steps of:providing a check valve mechanism which is sized to be positioned within the interior of a selected section of the pipeline, the valve mechanism being moveable between a first position which allows flow of fluids in a first direction and a second position which prevents the flow of fluids in a second, opposite direction, the check valve mechanism including a cylindrical mounting portion formed of a polyethylene material with a cylindrical exterior which is sized to be press-fit within the cylindrical interior of the selected section of pipeline to thereby install the check valve mechanism at a desired location within the pipeline; wherein the polyethylene material of the check valve mechanism is compatible with the polyethylene of the pipeline, whereby the check valve mechanism and pipeline materials tend to expand and contract at the same rate under the influence of temperature and pressure; wherein the check valve mechanism also includes a moveable valve element which cooperates with the cylindrical mounting portion of the check valve mechanism to control the flow of fluid through the pipeline, and wherein the moveable element is also formed of a plastic material; and thereafter joining an exposed end of the section of pipeline containing the check valve mechanism to a next section of pipeline in co-axial fashion by heat fusing the respective ends of the sections of pipeline, the valve body having an external diameter which is substantially equal to that of the remainder of the polyethylene pipeline. 5. The method of installing a back flow prevention device within a pipeline formed primarily of plastic material, the pipeline being formed of pipe sections having an exterior and a generally cylindrical interior, the method comprising the steps of:providing a check valve mechanism which is sized to be positioned within the interior of a selected section of the pipeline, the valve mechanism being moveable between a first position which allows flow of fluids in a first direction and a second position which prevents the flow of fluids in a second, opposite direction, the check valve mechanism including a cylindrical mounting portion formed of a plastic material with a cylindrical exterior which is sized to be press-fit within the cylindrical interior of the selected section of pipeline to thereby install the check valve mechanism at a desired location within the pipeline; wherein at least the cylindrical mounting portion of the check valve mechanism is formed of a plastic material which is compatible with the plastic material of the pipeline, whereby the check valve mechanism and the pipeline materials tend to expand and contract at the same rate under the influence of temperature and pressure; thereafter joining an exposed end of the section of pipeline containing the check valve mechanism to a next section of pipeline in co-axial fashion by heat fusing the respective ends of the sections of pipeline; wherein the check valve mechanism also includes a moveable valve element which cooperates with the cylindrical mounting portion of the check valve mechanism to control the flow of fluid through the pipeline, and wherein both the moveable element and the cylindrical mounting portion of the mechanism are formed of plastic materials; and wherein the cylindrical mounting portion is formed of polyethylene and the moveable element is formed of nylon.