An Overview of Plug Valve Types, Components, And Applications

author: ATHENA GROUP

2023-09-28

With plug valves, flow is stopped or throttled using conical or cylindrical plugs. When the plug is parallel to the flow, there is an opening at its center that allows flow through the valve when it is open. As soon as the controlling lever is rotated, the plug inside the valve assembly turns perpendicular to the flow, stopping the flow.

The purpose of this article is to give you a better understanding of plug valves.

Types of Plug Valves

Depending on their functionality, plug valves can be divided into four major categories: multi-port, eccentric, lubricated, and non-lubricated.

Multi-Port Plug Valve

A multi-port plug valve is a type of valve that has multiple outlets or ports, allowing it to control the flow of fluid or gas to different directions or destinations. It uses a rotating or sliding plug inside the valve body to open or close the passages to the various ports, providing flexibility in directing the flow.

Eccentric Plug Valve

Typically, eccentric plug valves operate their plugs in an eccentric path when they are closed, meaning the plug is offset from the center of the seating ring when they are operated. When the eccentric plug valve is open, it does not contact the seating ring.

Lubricated Plug Valve

A lubricated plug valve has small channels in the plug construction that allow for the flow of lubricant along the plug and its seating surface. The lubricant works along the length and seat of the plug. As a result of the lubricant, it is easier to close, open, and throttle a lubricated plug valve. A lubricated plug valve also prevents corrosion and promotes proper seating when closed.

Non-lubricated Plug Valve

A non-lubricated plug valve is typically used in low-pressure systems. In contrast to lubricated plug valves, non-lubricated plug valves have no automatic lubrication system and are more prone to deterioration and wear. This means non-lubricated valves are cheaper than their lubricated counterparts. Therefore, non-lubricated valves are perfect for applications with smaller actuator torque requirements.

Components of a Plug Valve

The plug valve consists of stem, body, disc, and bonnet, but it differs from other valves because it has a plug disc.

The Plug Valve Body:

A valve body consists of all the internal components of the valve. It connects to the pipes through an end connection.

The Plug valve Stem:

Plug valves have a stem that connects the disc (or disk) to the actuator. This helps in transferring the movement of the actuator to the plug disc, so the plug disc can be opened or closed.

The Plug valve disc

Out of all the valves, the plug valve, ball valve, and globe valve share some similarities. The plug disc, also known as a tapered disc, acts as a plug. Globe valves and plug valves have major differences in how their discs are designed. Globe valves have cylindrical discs, while plug valves are solid metal with tapered ends.

Plug Valve Ports

An important feature of plug valves is their adaptability to multiport configurations, which find widespread use due to several advantages:

Streamlined Piping and Installation: Multiport plug valves simplify the design of piping systems and ease installation procedures.
Enhanced Operational Convenience: They offer more convenient operation compared to managing multiple gate valves separately.
Cost-Effective: By incorporating multiple flow paths into a single valve, multiport plug valves eliminate the need for costly pipe fittings.
Reduction in Valve Count: Depending on the number of ports in the plug valve, it can replace up to four traditional shutoff valves, further reducing complexity.

Athena Plug valves come in various port patterns, each suited to specific applications:

Round Opening: This design features round ports in both the plug and body, facilitating smooth flow.
Rectangular Opening: The valve incorporates rectangular ports within its full bore section, optimizing flow control.
Standard Opening: In this configuration, the valve passage area is less than that of a standard pipe, providing specialized control capabilities.
Diamond Opening: With a distinctive diamond-shaped valve opening, this design offers unique flow management characteristics.
Multi-Port: Multi-port plug valves include three or more pipe connections, ideal for transferring multiple services through a single valve.
Venturi Design: Characterized by a reduced area opening that creates Venturi flow through the valve body, this design suits specific flow rate control requirements.

Application

The plug valve is typically used for on-off operations, especially where it is necessary to operate it frequently. It is not recommended for throttling applications because, like the gate valve, a high flow change occurs near shutoff.

Standard round port valves are used only when flow restriction isn't an issue.

Using venturi restricted flow type valves, diamond-shaped port plug valves are used for throttling.

Typically, plug valves are used to control gases and liquid hydrocarbons. Some water lines have these valves, as long as lubricant contamination is not an issue in some applications. There are also special applications for plug valves, such as throttling control in slurry services.

Pressure Balanced Taper Plug Valves

Typically, large taper-plug valves use pressure balanced plugs for very high static pressures. In an open valve, the line pressure can get into the larger end chamber beneath the plug if the plug is not pressure balanced. As a result, the plug is pushed into its tapered seat, which can result in taper locking.

The pressure balanced plug valve prevents taper lock by replacing the sealant pressure with the live line pressure by pressurizing the small end chamber.

Using the pressure balanced system, two chambers are connected to each end of the plug with the line pressure by two holes in the plug. There is a non-return valve at the plug's small end. By doing so, sealant pressure can be built up if necessary, while the line pressure can be accessed at the small end. Due to this, the pressure in the large end chamber is always equal to the line pressure, and the pressure in the small end chamber is always equal to or greater than the line pressure, preventing taper locking.

Advantages of Plug Valve

The main advantages of a plug valve include:

Excellent Shut-off Capability: Plug valves provide tight sealing when closed, preventing leakage effectively.
Simple and Reliable Operation: They are easy to operate with a 90-degree rotation, making them reliable for flow control.
Versatility: Plug valves are suitable for various applications, including throttling, on-off control, and isolation.
Minimal Pressure Drop: They offer low resistance to flow, resulting in minimal pressure loss across the valve.
Durability: Plug valves are robust and can withstand harsh environments and abrasive media.
Bi-Directional Flow: They can handle flow in both directions, providing flexibility in installation.
Adaptability to Multiport Configurations: Plug valves can be designed with multiple ports, simplifying complex piping systems.
Cost-Effective: They are often more cost-effective than other types of valves for certain applications.
Low Maintenance: With fewer moving parts, plug valves generally require less maintenance compared to some other valve types.
Wide Range of Materials: Plug valves are available in various materials to suit different applications, including corrosive and high-temperature environments.

Disadvantages of Plug Valve

The limitations or drawbacks of plug valves are as follows:

Higher Operating Force: Plug valves necessitate a significant amount of friction to rotate the plug, which can increase the force required to operate them.
Need for Actuators in Larger Valves: Larger plug valves often require actuators to assist with operation, adding complexity and cost.
Comparative Cost: Plug valves tend to be more expensive than ball valves with similar designs, which can impact the overall project budget.
Increased Pressure Drop: The presence of reducing ports in some plug valve designs can lead to a higher pressure drop, affecting system efficiency.

This article is just a brief introduction to plug valves, if you have any question or need further information about plug valves or other valves, please contact us via mail sales@athenavalve.com or direct call +39 06 87567444.