A plug valve is a type of valve shaped like a tapered cylinder or cone and can be rotated to control the flow of liquids. The plug of the valve rotates inside the plug body. The plug will have one or more hollow passages or ports often placed horizontally to enable fluid to flow when the valve is open.
A quarter-turn motion of the plug valve will align the pipe and the port, leading to an open state. The valve is closed when it is turned to a 90-degree angle from the open position and the solid part of the valve is positioned across the pipe, blocking the flow of fluid.
When the plug is conical, a stem or handle is usually connected to the larger diameter end of the plug.
Plug valves don’t have a bonnet but are connected to a handle attached to the plug end, which can be seen outside the valve body. The handle and stem are usually merged in a simple design as a single piece, with the handle typically in an L-shaped design.
Plug valves are generally inexpensive and simple in design used for many applications requiring hydraulic systems. For some chemical services, plug valve bodies are completely lined with PTFE, PVDF, PVDC, polyethylene, polypropylene, or similar coatings.
When is a plug valve used?
The quarter turn manual operated plug valve is used for stopping and starting the flow of liquids. They can also be used in on-off, basic moderate throttling, and diverting services.
While the most common plug valve design offers a straight two-way service, three-way plug valves are also common, where the third port is typically at a right angle to the inlet and the closure element is used to divert or combine the flow.
Types of plug valves
There are four main types of plug valves:
Lubricated Plug Valves
The lubricated plug valve uses lubricant for easy operation across a wide range of working pressures.
A layer of lubricant is placed between the body and the plug. The lubrication provides a good seal preventing any leakage. However, the valves need to be lubricated regularly.
This type of plug valve can handle abrasive or corrosive materials and does not get clogged.
Non-Lubricated Plug Valves
These valves don’t need lubrication and are commonly used in low-maintenance applications and in low-pressure lines. Because they are easy to maintain, these valves are often used in applications in which the fluids may solidify or get trapped and clog the valve.
The non-lubricated valve type includes elastomer sleeved, lift-type, and fully lined plug valves.
Expandable Plug Valves
The expandable plug valve has a complicated design, comprises many components, and uses a complex rotation motion that revolves between open and shut off position. This helps the protect the seal and avoids any wear and abrasion.
These valves are used in applications that don’t require double isolation and where media contamination needs to be avoided.
Eccentric Plug Valves
The eccentric plug valve contains a half plug, which makes it beneficial for applications that need a higher seating force with minimum friction from open to close positions.
These valves are used in isolation or flow control systems, such as sludge, air, slurries, sewage, and dirty and clean water.
Applications for plug valves
Plug valves find applications across many commercial and light industrial sectors and systems and are used for:
- Low-pressure low-temperature services
- Directional flow control
- Handling gas and liquid fuel
- Extreme temperature flow such as boiler feed water
- Regulating the flow of liquids containing suspended solids such as slurries
Advantages and disadvantages of plug valves
The plug valve offers the following advantages:
- Fairly economical and easy to maintain as the valve has a simple design and few parts.
- They open and close easily.
- The plug valves offer efficient flow regulation because of their ability to open quickly, shut off tightly and offer minimal resistance to flow.
- Maintenance and repairs can be done at the site of operation.
- There is less likelihood of corrosion or erosion as the plug and the body seating surface are not directly exposed to line fluid.
- These plugs can be used for a range of flow rates, including large flow rates.
The plug valve also has a few disadvantages:
- The cost of plug valves is more than ball valves.
- They require greater force to operate because of high friction.
- Larger valves require a gearbox or an actuator to be operated.
- Plug valves are not suitable for throttling operations.
- There can be a possibility of galling, a form of wear caused by friction and adhesion between sliding surfaces.
- The tapered shape of the plug can result in a reduced port, which leads to narrowing flows.
We offer a range of valves, including plug valves to suit your needs. Contact us to discuss your needs.
