Gas Plug Valve

What is a gas plug valve? 

This is a type of plug valve that is used in transporting gaseous and flammable products such as natural gas, steam, LPG, and chemical vapors. Gas plug valve manufacturers design this type of valve with a handwheel or valve actuator. The handwheel is used where the valve is to be manually operated by a valve operator. The valve actuator is used where the valve will be automatically or semi-automatically operated. Gas plug valves use a plug component to allow and block fluid flow. The plug has one or more holes where the fluid flows through. A gas plug valve manufacturer designs this type of valve with a cylindrical or conically tapered plug. The plug operates by rotating inside the valve via a threaded component known as the stem. The stem rotates for a quarter turn to open or close the valve. Gas plug valve manufacturers design this type of valve with strong materials to ensure the valve does not cause leakage as well as make it strong against high temperatures. 

Figure: Gas plug valve.

Components of a gas plug valve 

Valve body 

This is the main component of a gas plug valve used to house internal parts of the valve. Gas plug valve manufacturers design the valve body using strong metallic materials such as ductile iron, cast iron, stainless steel, and carbon steel among other strong materials. The valve body contains the inlet and outlet valve ports where fluid flows into and out of the valve. 

Valve plug 

This is the part of a gas plug valve that is responsible for opening and closing fluid flow. The plug is designed with holes where the fluid from the pipe flows through the valve. The plug materials determine the area of application.

Valve seat 

The seat is a component placed between the valve body and the valve plug to prevent fluid leakage when the valve is closed. The valve seat provides a surface where the plug rests when the valve is closed. 

Stem

This is the part of a gas plug valve designed with threads so that it can be turned by the handwheel/lever to provide torque to the plug so that it can open or close the fluid flow. The stem connects the handwheel/lever or actuator to the valve plug. The stem is rotated to make only a quarter turn allowing or blocking fluid flow. 

Handwheel/ actuator 

The handwheel is a component of a gas plug valve in which the valve operator applies force to open or close the valve. The actuator is a component that is used in automatic gas plug valves to provide the torque necessary to turn the stem to open or close the fluid flow. The actuator can be electric, hydraulic, or pneumatic. 

Packing 

This is a component of a gas plug valve used to prevent any leakage of fluid through the stem. 

Figure: Components of a gas plug valve.

How does a gas plug valve work? 

Gas plug valves are designed with conical or parallel seats where the plug rests. The plug is designed with one or more ports. It is the position of the ports that determine if the valve is in the open or closed position. A quarter turn angle of the plug ensures the valve is either in the open or closed position. Gas plug valves operate in the fully open or fully closed position and they are not suitable for use in the throttled position. When the ports of the plug and the ports of the valve are aligned, fluid starts flowing through the gas plug valve. To close the fluid flow, the plug is rotated by the handwheel via the stem at an angle of 90^o degrees. This aligns the plug ports perpendicular to the fluid flow. This ensures fluid does not access the ports and thus no fluid flow. 

Figure: Working of a gas plug valve.

Types of gas plug valves 

Lubricated gas plug valve 

This is a gas plug valve designed to use lubricant for ease of operation over different levels of pressure. A lubricated plug valve has a lubrication layer between the plug component and the valve body. The lubrication layer serves as a seal and also prevents any fluid leakage. Gas plug valve manufacturers recommend lubricating this type of valve regularly to ensure smooth operation as well as enhance service life. The sealant material used should be such that it can withstand fluid temperature as well as debris or slurries associated with the fluid. As such, gas plug valve manufacturers design this type of valve with an effective sealant material with chemical resistance, enough resilience, and which is waterproof around any part of the valve body. The lubricant also helps to prevent the formation of corrosion on the metallic material between the plug and the body. 

Non-lubricated gas plug valve 

This is a gas plug valve that does not have a lubrication film. Gas plug valve manufacturers design this type of valve for use in low-pressure applications. The valve is designed with an elastomeric body liner or sleeve. This liner or sleeve is installed in the valve body cavity. The plug is tapered and polished and works as a wedge to compress the liner against the valve body. As such, the liner helps to reduce the friction between the plug and valve body. Non-lubricated gas plug valves have less maintenance levels compared to the lubricated types. Gas plug valve manufacturers recommends these valves for use in applications where fewer maintenance levels are required. 

Eccentric gas plug valve 

This is a gas plug valve designed with a half plug. The half plug is in the form of a cone or ball shape. These valves are suitable for use where there is need for high seat force and less friction from the open to the closed position. The eccentric plug valve has excellent closure which helps to ensure no fluid leakage.

Multi-port gas plug valves 

This is a gas plug valve designed with more than onemport. Gas plug valve manufacturers design this type of valve for use to transfer and divert fluid flow. One multi-port gas plug valve can serve the task of three or four globe or gate valves. 

Threaded end gas plug valve 

This is a gas plug valve that is connected to the pipe using threads. This type of valve is used in medium and low-pressure applications. However, depending on the materials used to make internal parts the valve can be used at low and high temperatures. Gas plug valve manufacturers design this type of valve with male or female threads. If the valve is designed with female threads, the pipe end to be connected is designed with male threads and vice versa. Threaded end gas plug valves are small in size and light in weight compared to the bolted type. 

Figure: Threaded end gas plug valve.

Flanged end gas plug valve 

This is a gas plug valve that is connected to the pipe using bolts and nuts. Gas plug valve manufacturers produce this valve with flanges at the ends. The flanges have holes where the bolts are inserted. Flanged end gas plug valves have high strength and are recommended for use in high-pressure applications. Flanged end gas plug valve manufacturers use strong metallic materials to make these valves making them strong. These valves are easy to install and assemble. However, these valves are heavy due to the bolts and nuts used as well as flanges designed on the valve. 

Figure: Flanged end gas plug valve.

Welded end gas plug valves 

This is a gas plug valve that is connected to the valve using the welding method. Gas plug valve manufacturers recommend use of this type of valve where fluid leakage could be hazardous such as in flammable products. This valve cannot be opened for inspection or cleaning while in the field unless the weld is removed first. Welded end gas plug valve is suitable for use where the valve does not need to be cleaned and where frequent repair is not needed. This type of valve guarantees zero fluid leakage and thus using it in flammable and very hot fluid enhances safety to the valve operator. 

Applications of Gas plug valves 

• Transportation of liquefied natural gas. 
• Steam power generation plants ensuring no steam leakage. 
• Processing of hydrocarbons. 
• Heating, ventilation, and air-conditioning systems (HVAC). 
• Compression systems. 
• Manufacturing of gases such as oxygen, and nitrogen among others. 

Advantages of gas plug valves 

• Used in various industrial applications due to their versatility. 
• They are free from fluid leakage if used according to the instructions given by the gas plug valve manufacturers. 
• Simple and compact design. 
• Durable as they can be used for a long period without being replaced or repaired. 
• They can be used in high pressure and high temperatures. 
• These valves have few rotating parts which reduce wear of parts and thus maintenance cost. 
• Operate quickly as they only need a quarter turn to either open or close fluid flow. 
• They have high efficiency because the pressure drop is low compared to other valves like gate valve.

Disadvantages of gas plug valves 

• Large gas plug valves cannot be opened or closed manually and thus they need an actuator. 
• These valves are not best for use in throttling applications.
• They need more torque to open and close. 

Troubleshooting gas plug valves 

Internal fluid leakage 

• Blockage in the valve. Open the valve according to the gas plug valve manufacturer’s instructions and remove any materials causing blockage. 
• Damaged or worn-out seat. Replace the valve seat. 
• Damaged or worn-out O-rings. Replace the O-rings. 

External fluid leakage 

• Loose connection of the bolts or threads. Tighten the connecting elements to the torque values recommended by the gas plug valve manufacturer. 
• Worn out or damaged gasket. Replace the gasket. 
• Worn out or damaged packing. Replace the valve packing. 

The handwheel is hard to rotate 

• Materials clogged between the stem and the cover. Remove the materials. 
• Damaged stem. Replace the stem. 

The gas plug valve produces a lot of noise or vibration 

• Excess fluid flow velocity. Ensure the fluid flow velocity is at the level recommended by the gas plug valve manufacturer.

Summary 

A gas plug valve is a type of plug valve used in the transportation of gaseous products such as steam, gas, vapor, and similar products. Gas plug valves allow and block fluid flow by using a plug component with two or more ports. The plug works by being aligned with the valve ports allowing fluid flow. The gas plug valve is closed when the plug ports are rotated to become perpendicular to the valve ports.

Gas plug valve manufacturers use different materials to design and manufacture these valves for use in different levels of pressure and temperature. The valve should be used according to the gas plug valve manufacturer’s instructions to help the valve live longer and reduce maintenance costs. These valves are either manual or automatic. The automatic ones are operated using actuators such as hydraulic, electric, or pneumatic.