This invention relates to gate valves. Gate valves generally comprise a body furnished with an internal gate cavity positioned generally perpendicular to a flow bore which extends through the body communicating the cavity to the inlet and outlet bores. A gate is positioned in this cavity, the gate being movable by external means. With the gate in its closed position flow between the inlet and outlet bores is sealed and with the gate in its open position full bore flow is allowed.
Gate valves are known which have seat mechanisms either side of the gate which engage the body surfaces surrounding the inlet and outlet flow bores through the body together with gate sealing faces. Such seats are generally disposed in annular recesses known as seat pockets provided in the body around the inlet and outlet bores at positions where they communicate with the gate cavity.
Many arrangements are known for such seat structures. A problem with such structures is to provide an effective full metal seal between the seat and the body which not only gives a consistent seal but also protects the critical sealing surfaces from well bore particulate contamination. Arrangements are known for example where non-metallic seals have been provided either on the end face of the seat where it abuts the body or on the seats outside diameter.
Another arrangement uses inner and outer metallic sealing rings, such as metal C-ring seals, located in inner and outer grooves on an end face of the seat and the seat is locked in position in its recess by means of a locking ring which engages an outer circumferential surface of the seat, the locking ring itself being held in position by a retainer wire. The locking ring is used to load the seat against the body energising the C-ring seals, effecting a seat/body seal. Known problems exist with this particular design, mainly due to the uneven loading of the seat mechanism after installation leading to reduced sealing capabilities.
The A. U. Bryant U.S. Pat. No. 2,777,664 discloses various shapes of metal-to-metal seals for use with gate and ball valves. Those structures suitable for use with a gate valve require a welding of the seal body to the valve body.
The E. E. Hulsey U.S. Pat. No. 3,497,177 shows a seal assembly for a gate valve whereby a Belleville spring is used to maintain an elastomer seal in face-to-face contact with the gate. No provision for metal-to-metal sealing is made.
The Allen U.S. Pat. No. 3,771,545 discloses a Bellville spring used in a ball valve to maintain an elastomer seal ring in sealing engagement with the spherical closure member.
The Kindersley U.S. Pat. No. 4,217,923 shows a spring metallic cylindrical bellows with convolutions in combination with a C shaped metal seal on a valve seat used in a ball valve.