This invention relates to a butterfly valve and the method of manufacture and in particular to a multi directional butterfly valve made from plastic, such as, polyethylene, polypropylene and similar materials.
The use of butterfly valves in various applications including pipeline service in the oil and gas industry are well known. Such butterfly valves are useful in gathering pipelines, as well as, transmission and distribution pipelines. Previously, butterfly valves have primarily been made from metallic material, such as, stainless steel, carbon steel, etc., and more recently plastic has come into use for manufacturing butterfly valves.
In relatively high pressure service, e.g. 160 PSI or more, sealing between the valve body and the flow control valve disc is difficult and frequently leaking occurs around the disc and in some cases the control valve stem is subject to being blown out because of faulty seals.
The problem with sealing in butterfly valves has been approached in various manners. U.S. Pat. No. 2,987,072, to Muller describes a butterfly valve which uses a sealing element that seats in a circumferential groove in the valve body. The sealing means comprises a continuous elastomer with an integral pair of eyelets diametrically opposed from each other which are rotated 90.degree. to accommodate the valve shaft to provide sealing between the shaft and the valve body.
U.S. Pat. No. 3,329,394, to Overbaugh, although directed to a lockable valve handle, discloses a resilient valve seat for sealing the valve when it is closed and o-rings to seal the valve stem.
U.S. Pat. No. 3,726,503, discloses a butterfly valve with a pressure seal. The seal consists of two members arranged to contact the valve disc when the valve is closed and the two members of the seal are so constructed that fluid under pressure may pass between the interface of the two members to the radially outmost side arranged to exert pressure against the outermost sides of the two members, thus causing additional sealing pressure against the periphery of the valve disc.
The problems associated with valve manufactured from plastic, such as, polyethylene are outlined in U.S. Pat. No. 4,348,006 granted to Schmitt, et al. Schmitt points out that the valve seat requires the use of elastomeric material, although such materials have a tendency to creep or migrate when subjected to high pressure especially with pressure applied to the seat on one side of the closure disc only. This problem has caused industry to use reinforcing members in the seat. Schmitt states that the known arrangements for maintaining a seal directly on a valve body of polyethylene are considered ineffective and permit leakage past the closure. Schmitt's solution to the problem is to provide a valve assembly that includes a valve body of plastic material in which the valve seat includes a metallic sleeve member molded in the plastic valve body in such a fashion as to lock the metallic sleeve member in the plastic valve body to prevent separation therebetween. The valve stem is sealed by a pair of o-rings separated by spacer members surrounding the valve stem and retained about the valve stem by a metallic retainer having a serrated periphery embedded in the body of the annular portions.