Plug Valves

Materials Used

Types

Parts

Uses

Plug valves are one of the most popular category of pipe vales used in variety of applications. Also known as cock or stop-cock valves, plug valves have been in use since a long period of time. Infact, they were developed for use in citywide Roman plumbing systems and remain as one of the most widely used valves for both on/off and throttling services.

They are a kind of rotational motion valves which are used to stop or start fluid flow. They are so called because of the shape of the disk, which resembles a plug.

Types of Plug Valves:
Plug valves are made with tapered and cylindrical plugs and are available in various types like given below:

• Nonlubricated plug valve: This is the earliest form of plug valve. A nonlubricated plug valve may use a tapered plug having a mechanical lifting device, which unseats the plug before it is turned to reduce the operating torque required. It may also have an elastomeric sleeve or plug coating with a low coefficient of rubbing friction. Though this design is still in use, the problems with galling and sticking limit their usefulness.
• Lubricated plug valve: The lubricated plug valves were developed to overcome the difficulties of non-lubricated plug valves. In this type of plug valve, the lubricant is forced into the valve under pressure. The lubricant prevents leakage between the plug and body. The lubricant also reduces friction and wear between the surfaces when the plug is turned. The use of lubricant between the plug face and the seat eliminates most of the problems of nonlubricated valves.
• 2-port valve: This kind of plug valve has two positions—one which is open to allow flow, and the other to shut or close to stop flow. Ports are openings through which fluid can enter or leave in the valve body.
• 3-way plug valve: In this type of plug valve, there are three ports and flow from one port could be directed to either the second or third port. A 3-way plug valve can also be designed in such a way to shift flow between ports 1 and 2, 2 and 3, or 1 and 3. They can also connect all three ports together.

Parts of plug valves:
The body of the plug valve comprises three parts:

• Body
• Cover
• Plug

The plug is a cylindrical, tapered or cone-shape mechanism that can raise or lower within the seat to restrict, maintain or completely shut off flow. The plug valve is opened by rotation and the plug is the only element that is capable of movement.

A diagrammatic representation of plug valve is given below.
The body of a plug valve is designed to receive the tapered or cylindrical plug.



Uses of plug valves:

• Plug valves are high capacity valves that are found widely in-
  • low-pressure sanitary applications and
  • industrial applications, like petroleum pipelines, chemical processing and related fields, and power plants.
• They are extremely versatile valves that can be used for directional flow control.
• They can be used even in moderate vacuum systems.
• Plug valves can efficiently handle gas and liquid fuel.
• They can safely handle extreme temperature flow, such as boiler feed water, condensate, and other such elements.
• Plug valves can be used to regulate the flow of liquids containing suspended solids, for example, slurries.

Industries Using Plug Valves:

• Air Conveying
• Automobile plants
• Atomic Energy Installations
• Bakeries
• Chemical industry
• Dairies
• Fertilizer plants
• Iron and steel industry
• Testing laboratories etc.