1. Field of the Invention
The invention pertains to the field of gate valves. More particularly, the invention pertains to expanding double disk gate valves.
2. Description of Related Art
Industrial valves provide accurate control of high-pressure fluid or gas flow. Gate valves are often used where fluid flow or gas flow is seldom interrupted, and accurate regulation of flow quantity is a prime consideration. Gate valves allow maximum flow while exercising flow control through the closure of a sliding gate transverse to the direction of flow in a flow channel.
The gate is user controlled through an operating stem such as a spindle screw or other types of operating stems and mechanisms. These operating stem mechanisms open and close the gate and also allow adjustments in flow rate by positioning the gate in intermediate positions in a flow channel. The primary advantage of a gate valve is that the nominal working flow rate of the fluid or gas is not reduced by installing the hollow valve body.
Various types of gate valve assemblies are known for opening and closing pipelines to control the flow of fluid or gas. The traditional gate valve employs a single metallic disk that is movable between an open position and a closed position transverse to a flow channel to stop or allow flow of a liquid or gas from an inlet through the gate valve and out through an outlet.
Single disk gates are typically mounted in valve bodies and seating channels with a small amount of play, so that pressure on an inlet side of the disk biases the gate toward a valve seat in the hollow valve body when the gate is in a closed position. This play may, however, allow leakage around the gate and the valve seat, and over time may result in wear that may require repair or replacement of the gate valve or the gate disk assembly.
Alternatively, single metal disks with close tolerances that more effectively seal flow when the gate is in a closed position can be subject to friction between the gate disk and the valve seat surfaces of the hollow valve body. Friction between the gate disk and the valve seat may hinder movement of the gate disk, and over time cause wear on the gate disk and/or valve seat that similarly degrades the sealing capacity of the valve seal and necessitates repair or replacement of the gate valve body or gate disk.
In the prior art, Kennedy (U.S. Pat. No. 4,483,514, “Gate Valve Member For Resilient-Seated Gate Valve”) describes a valve gate disk assembly with two disks that reduces leakage and valve gate play. The two disks are positioned between two opposing valve seat surfaces in the hollow valve body. One disk is adjacent an inlet and the other disk is adjacent an outlet of a gate valve body. When closing the gate valve, the gate disk moves into the gate valve body, and the double disk construction sealingly engages the respective valve seat surfaces as the gate disk assembly moves into a fully closed position. The gate disks may be pressed outwards against the valve seats by a spring assembly, or by fluid pressure introduced between the gate disks.
Tiefenthaler (U.S. Pat. No. 4,913,400, “Double Disk Gate Valve”, issued in 1990) describes a prior art double disk gate valve in which two disks are biased outwardly toward valve seat surfaces by fluid pressure. In this construction, a fluid medium is used to force the two gate disks apart through the use of pistons, cylinders, valves, and channels or piping that regulate the flow and pressure of the fluid between the two gate disks at open and closed positions.
Kennedy (U.S. Pat. No. 6,254,060, “Gate Assembly for a Double Disk Gate Valve”, issued in 2001) describes another prior art dual disk gate valve in which an elastomeric material is positioned between two gate disks. In this construction, a cross member is included between the two gate disks, comprising a gate assembly attached to an operating stem, and in contact with the elastomeric material between the two gate disks. When the gate assembly is moved into a closed position, and when the gate disk assembly reaches a closed position pressing against the hollow valve body, the cross member is forced toward an opposing position of the hollow valve body. The cross member thus compresses the elastomeric material between the two gate disks, and this compressive force is translated outwardly against the two gate disks forcing them to positively seal against valve seats in the hollow valve body.
Gate valve assemblies employing double disk closure gates have been improved upon through the incorporation of elastomeric sealing material around the periphery of the gate disks. When the gate assembly is moved into a closed position in the hollow valve body, the elastomeric material located on the peripheral surfaces of the gate assembly are deformed at the valve seat surfaces through the application of pressure to the gate assembly, thereby helping to provide a tighter seal between the valve seat surfaces and the gate assembly than can be accomplished by bare metal disks alone.
Prior art configurations employing elastomeric sealing members around the periphery of a gate assembly must be constructed with narrow tolerances to ensure positive sealing characteristics. These tolerances must be even more precise when side wall portions of the valve seat surface perpendicular to the direction of gate travel are considered. The prior art typically mounts these elastomeric sealing members on the periphery of the gate assembly, making the dimensional tolerances of the elastomeric sealing member very narrow, to prevent compression of the elastomeric sealing member beyond its elastic limit. Maintaining narrow tolerances of elastomeric sealing members and valve seats requires significant manufacturing oversight, is time consuming, and is a cost factor limiting the application of double disk gate valves.
Further, in some prior art configurations, the pressure available for forcing gate disks outwardly against valve seating surfaces may be limited, delivered by complex structures, and/or unevenly applied about the circumference of the gate valve. These factors may negatively impact the reliability of these constructions, further increase costs, and may limit the diameter of flow channels in which they can be employed, as well as the maximum operating pressures of fluid flow they may effectively control.
For example, when an elastomeric material is located between two gate disks and compressed by a cross member, compression of the elastomeric material may not be uniformly distributed throughout the elastomeric material. Portions of the elastomeric material closest to the cross member may experience greater compression than portions of the elastomeric material that are farthest from the cross member. As a result, the outward pressure on the two gate disks may be greater near the cross member than at a location diametrically opposed to the cross member. This condition may limit the maximum diameter valve in which such a solution may be implemented.