What is a Plug Valve and When is it Used

What is a Plug Valve and When is it Used

Plug Valve Basics

    A plug valve is shaped like a cylinder or

cone and can be rotated inside the valve body to control flow of fluids. Plug valves have

one or more hollow passageways often placed horizontally to allow ease of flow through the

valve when open. The most common type of plug valve is the 2 port model with an open and

closed position. The two ports are usually located on opposite sides of the valve with one

passageway leading from inbound to outbound and the stem and handle located on the top. A

plug valve also uses a quarter turn valve, which is useful where quick and frequent

operation is essential. The valve ends can be flanged, hub type, or butt weld.
    Plug Valve Types and Their Uses
    Although there are many types of plug valves, there are four general categories, each

with their own benefits.
    1. Lubricated Plug Valve
    As the name suggests, a lubricated valve uses a lubricant usually made up of a base

oil and viscosity improver (like amorphous or fumed silica) that is injected under pressure

between the plug face and body seat to reduce friction and seal ports. Valve manufacturers

generally recommend lubricant suitable for the process fluid, and the valves often must be

resealed after only a few cycles, and in some cases, after every cycle. Considered a high

maintenance plug valve, they are often used in applications that have infrequent

operations. Lubricated plug

valves perform well in processes that utilize fluids which carry mildly abrasive

particles such as dirty upstream applications, gas pipeline systems that need bypass

valves, and as blow-down valves on valve stations and kicker valves.
    2. Non-Lubricated Plug Valve
    This plug valve utilizes a tapered or cone-shape that acts as a wedge and presses a

polymeric sleeve against the body cavity. The use of the Sleeve Type Soft Sealing Plug Valve

reduces friction between the plug mechanism and body.  Non-lubricated plug valves are often

used instead of lubricated ones in applications where maintenance needs to be kept to a

minimum, such special services in sulphur, hydrogen fluoride, or where liquids could be

trapped or solidify and potentially jam the valve. However, non-lubricated plug valves are

limited by temperature and chemical compatibility of the non-metallic materials they are

made of.
    3. Eccentric Plug Valve
    The design of this plug valve uses a half plug that is advantageous for applications

needing a higher seating force with minimal friction from open to closed position. The

torque seated valves also feature improved shut off capabilities.

Eccentric plug valves are

used for a wide range of flow control and isolation applications including clean and dirty

water, sewage, sludge and slurries, air, and other services.
    4. Expanding Plug Valve
    This complex plug valve uses multiple components that allow the valve to mechanically

expand and give it a true double block and bleed function in one valve. The plug valve uses

a mechanism that rotates between the open and closed position and protects both seals from

the flow path. During rotation there is no contact between body and seals, and slips expand

onto the body seat when the valve is closed to avoid causing any wear or abrasion to the

seals. They are often used to prevent product contamination in applications that do not

require a double isolation.
    In conclusion, General Valves have a

number of useful applications, and new technology and designs are sure to give them an even

wider variety of applications within many processes. And if you need more information on

different types of valves, check out this piece on check valves or the rest of the site.
    Ball valves are one of the quarter-turn

valves along with plug valves and butterfly valves. They are widely used in piping systems.

They can be operated manually or by using an actuator. The simplest operation of a ball

valve is through the use of a wrench or a lever manually turned by an operator. A torque is

applied to rotate the lever arm by 90° by either clockwise or counterclockwise to open or

close the valve. If the lever arm is parallel to the pipe,

Floating Ball Valve

indicates that the valve is open. On the other hand, if the lever arm is perpendicular to

the pipe, it indicates that the valve is closed. The operation of a ball valve is only

limited to shut-off and on. It is not advisable to utilize ball valves for throttling as

they lack fine controls for flow rate regulation. Ball valves come in many designs and

features to satisfy various industrial needs.