A Process Industry Stalwart - The Plug Valve

Lubricated plug valve.
(Flowserve Durco)

This article will focus on one of the oldest and most reliable (when properly applied) industrial valve types - the plug valve.

Fluid process control operations commonly employ pumps, piping, tanks and valves as the means of transporting, containing and controlling the fluid movement through a system.

Valves, of which there are many types, provide control over the flow rate, direction and routing of fluids in a processing operation. Flow can be started, stopped or modulated between zero and full rate using a properly sized and configured valve. Some valves enable media flow to be diverted to a selection of outlets, in lieu of a single inlet and outlet pair. Specialized valves regulate inlet or outlet pressure, or prevent fluid flow from going in an undesirable direction. All of these capabilities are packaged into differing valve product offerings that present a very large selection array to a process designer or engineer.

Non-lubricated plug valve.
(Flowserve Durco)

Industrial flow control valve types are generally classified according to the structure or arrangement contained within the valve body that provides obstruction to fluid flow. Some of the common types are ball, butterfly, gate, globe, and plug. Surely, there are more valve types, and this article is not intended to list them all. Some of our previous blogs have discussed selection considerations for gate, ball and butterfly valves.

Plug valves, like ball and butterfly valves, span from fully open to fully closed positions with a shaft rotation of 90 degrees. The “plug” in a plug valve is installed in the flow path within the valve body and rotated by means of a stem or shaft extending to the exterior of the body. Plugs are tapered toward the bottom and are fitted to a seating surface in the valve body cavity that prevents fluid from bypassing the plug. An opening through the plug, the port, can be shaped to provide particular flow characteristics. There are two main types of basic plug, lubricated and non-lubricated. Lubricated plug valves have a cavity into which a sealant is injected. The sealant provides a renewable seal between the plug and the body, prevents internal leakage, and protects the seating surfaces against corrosion. Non-lubricated plug valves utilize an elastomeric body liner or a sleeve in the body cavity that is pressed in to the body of the valve by the plug's wedge-like shape,  with the result of reducing the friction between the plug and the body.

Plug valve considerations:

• 90 degree rotation from open to closed provides fast operation.
• With proper configuration, can be well suited for frequent operation.
• Availability of corrosion resistant liner may provide comparative cost savings because valve body can be constructed of less expensive material.
• Design is simple and employs a low parts count.
• Valve can be serviced in place.
• Generally, low resistance to flow when fully open.
• Reliable leak-tight service due to tapered plug wedging action, replaceable sleeve, and injection of lubricant in some variants.
• Potential issues of concern for plug valve application include a short list of items.
• Higher friction in the plug closure mechanism may require comparatively higher operating torque than other valve types.
• Without a specially designed plug, generally not well suited for throttling applications.
• Rapid shutoff delivered by plug design may not be suitable for some applications where hammering may occur.

Share your fluid control application challenges with a valve and automation specialist. Leverage your own knowledge and experience with their product application expertise to develop an effective solution.

Solenoid Valves - How They Work

Solenoid valve, 2-Way, Brass
(ASCO)

Solenoid valves are used throughout many commercial, municipal, industrial, and even residential settings to manage fluid flow. What we refer to as a solenoid valve is an integrated valve and actuator. The actuator, or solenoid, operates via electric current flowing through its helix shaped coil. Energizing the coil with a control signal produces a magnetic field, which then actuates the valve mechanism. Depending on the port configuration of the valve, solenoid valves can either function as two way flow controllers or as diverters in a process system, If the valve contains two ports, then the valve is an on/off valve. If the valve contains three or more ports, then the valve directs the flow of a fluid in the process system. Thanks to their flexibility, reliability, and need for only a small amount of control power, solenoid valves are a frequently used fluid process control device.

The solenoid used in a solenoid valve functions as a converter for electrical energy, using the supplied electrical energy to produce mechanical energy. Metal or elastomeric seals on solenoid valves can be coupled with electrical interfaces, allowing for relatively easy operation by the process controller. The valves typically use a metal plug to cover up a hole, and when pressure from the process fluid is applied to the valve, the pressure difference causes the solenoid valve to be in its normal position. Instead of referring to two directions of flow, the two-way solenoid valves are named two-way because these valves contain two valve ports which the fluid uses to travel.

Three way valves, similar to the name of the two-way valve, have three fluid ports. In an application example, these ports could correspond to pressure, exhaust, and cylinder. In a pneumatic system, these would be used for compressed air supply, vent, and the actuating mechanism. Regardless of the application, the valve function is the same, connecting the inlet port to one of two outlet ports. The selection array of solenoid valves for commercial and industrial use is vast, with variants suitable for a wide range of media, pressure, temperature, and operation sequence.

Pneumatic and hydraulic systems are typical applications for solenoid valves, as are processes such HVAC, where solenoid valves help control liquid refrigerant, as well as suction and hot gas lines. Solenoid valves are a popular fluid flow control options used in processing industries.

Share your fluid control requirements and challenges with application experts, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Watch the video below for more on how solenoid valves work.