Mainline Valves

In various industrial systems, such as those comprised of complex pipelines, valves are essential in controlling the flow of liquid and gas. As a result of the wide number of systems that valves can serve, valves have evolved to meet varying application requirements including significant amounts of pressure and high amounts of liquid or gas. In mainline transmission there are several kinds of mainline valves: gate, ball, plug, and check valves. However, these valves are not exclusively used for mainline transmission, and have other uses in different applications. Other valve categories include industrial valves and control valves.

Mainline Valves

Mainline valves’ primary function is to enable or inhibit the central flow in a pipeline system, be it gas or liquid, thus enabling the rest of the system to operate smoothly. Gate valves, ball valves, plug valves, and check valves all fall into this category.

• Gate Valves

A gate valve opens and closes as a result of a round or square wedge or gate moving in and out of place. Because the sealing surfaces between the gate and the seat upon which the square wedge sits are planar, an open gate valve generates a nonlinear flow path and an inconsistent flow rate. It is intended to be either completely open or completely closed and is not generally used to regulate flow.

• Ball Valves

A ball valve relies upon a ball with a hole in it, attached to a handle. When the handle is turned, the ball rotates until the hole is aligned with the valve, thus enabling flow. When the valve is closed, the hole in the ball is not aligned with the valve, thus inhibiting flow. The handle’s position is indicative of the ball’s position: if the handle is perpendicular to the valve, the hole is also perpendicular and the valve is closed. If the handle is in line with the valve, the hole is also in line and the valve is open. Ball valves are versatile, durable, and often used in shutoff applications. They are also suitable for applications with up to 10,000 psi.

• Plug Valves

Plug valves use cylindrically or conically shaped plugs to block the valve openings or enable flow. The most common types of plug valves have only two positions, either open or shut. However, plug valves can also feature three openings, thus enabling a valve to shift flow between three different lines. Because of the nature of plug valves, they are commonly used in application where they either start or stop flow. Additionally, because the valve seatings are removed from the fluid path completely when the valve is open, a plug valve can move fluids with suspended solids without damaging valve seatings. Lubricated plug valves are especially well-suited to handling abrasive fluids.

• Check Valves

A check valve differs from other mainline valves in that it only permits the flow of liquid of gas in one direction, thus preventing the reversal of flow. Because they only operate in one direction and are automatic, they do not require any handle and most do not require manual manipulation. When flow moves forward check valves open; when flow is reversed check valves close. Depending on the manner in which the closing device moves into place, there are several different groups of check valves. In swing check valves, for example, a hinged device swings into place to close the valve. In tilting-disc check valves, a hinged device is also used but the hinge is mounted differently.