VALVE IN THE OIL AND GAS INDUSTRY
All types of valves are designed to start, stop, or throttle the flow of a medium. Gate valves are primarily suited for fully open or fully closed services. That means you can install them in pipelines as isolating valves, but not control or regulating valves. A gate valve works by lifting a circular or rectangular gate out of the medium’s path, which can either be oil or gas. When you fully open the valve, the gate valve is full bore indicating that there is nothing to obstruct the medium’s flow since the pipeline diameter and the gate have the same opening. The bore diameter is also the determinant of the valve size. Since the valve has to turn several times to go from an open to a closed position, the slow process helps prevent fluid hammer effects.
Gate valves come in handy for various uses in the oil and gas industry and can be used for either above ground and below ground installations. But for underground structures, it is wise to choose the right type of valve as the replacement costs can be very high. Let us look at how gate valves work.
Gate valves come in different designs:
Expanding Gate Valves
An expanding gate valve, also known as a WKM Pow-R-Seal Valve, has two units, which is a gate and a segment. The two units collapse against each other during flow and separate when the valve is fully open or fully closed to affect a mechanical seal. That is unlike a slab gate valve, which usually has one unit.
Slab Gate Valves
A slab gate valve has one gate unit that raises or lowers between a pair of seat rings. It is mainly used for transporting crude oil.
Wedge Gate Valves
A wedge gate valve is designed with a tapered gate that includes a metal to metal sealing. Compared with an expanding gate valve and slab gate valve, a wedge gate valve is not pingable. That is because of the empty void left at the bottom of the valve body when it is open. The valves do not have a bore through the gate but instead, the gate contracts into the valve body when it is open, saving the height space.
Knife Gate Valves
A knife gate valve is useful in cutting through too thick fluids. This valve has a design that makes it self cleaning because it clears the knife of its abrasives with every stroke as it passes the seat rings and skirts. The gate unit in the knife gate valve is thinner than other gate valves. That is because the water type body that sandwiches the gate guides it in place.
Gate valves have a rising or non-rising stem design. Rising stems attach directly to the gate and give a visual indicator of the valve position. Non-rising stems thread into the upper part of the gate with a threaded pointer on the top to indicate position. Gate valves also have a sealing unit to facilitate a tight seal on the stem.
Gate valves are designed with one of the four types of bonnets to prevent fluid leakage from out of the valve. There are union bonnets, pressure seal bonnets, screw-in bonnets, and bolted ones.
Gate valves are suitable for most fluids, including water, oil, air, steam, and gas; hence very useful in the oil and gas industry.