Plug valve has been commonly used in different situations for a long time. It’s becoming popular by its simple but solid structure design and low in fluid resistance.
This article will give you a more knowledge about plug valve.
WFE Plug Valves
The plug valve design, plug port types
Basic design of the valve the disk is a solid tapered or cylindrical plug with a bored passage - port at a right angle to the longitudinal axis of the plug as shown in Figure 1. The plug valve body is machined to receive a tapered or cylindrical plug.
Figure 1. Design of 2-way plug valve
Operating principle
The operation of the valve is very simple: a rotary plug with port opening permits or blocks the flow of liquids or gases depending on the plug port position in relation to a pipeline. As Figure 1 shows, in the open position, the passage in the plug lines up with the inlet and outlet ports of the valve body. When the plug is turned 90 degrees from the open position, the solid part of the plug blocks the ports and stops fluid flow. For throttling operation
Types of plug valves
There are various types of port openings, each with a varying degree of area relative to the corresponding inside diameter of the pipe. Rectangular port is most common and come with 70% or more of cross-sectional area of corresponding type. Round port plug comes as full port type, where port diameter is equal or larger than pipe diameter. Standard - round port plug have port diameter smaller than corresponding pipe diameter. Third common port type is diamond port plug. Plug valves come in lubricated or non-lubricated types. The lubricated plug valve should be specified for hard-to-seal substances. The plug is designed with grooves, which retain a lubricant to seal and lubricate the valve. Two basic types of non-lubricated plug valves are lift-type and elastomer coated sleeve or plug. Lift-type valves provide a means of mechanically lifting the tapered plug slightly to disengage it from the seating surface to permit easy rotation. Plug valve having an elastomer sleeve design results in a primary seal being maintained between the sleeve and the plug at all times regardless of position. It has a low coefficient of friction and is therefore, self-lubricating. Besides classic two port valve, various versions of multi-port valves are widely used. Their installation simplifies piping, and they provide a more convenient operation than multiple gate valves. In most cases, one flow-path is always open. These valves are intended to divert the flow of one line while shutting off flow from the other lines. If complete shutoff of flow is a requirement, a multi-port valve designed to permits this must be used, or a secondary valve should be installed on the main line ahead of the multi-port valve to permit complete shutoff of flow. In some multi-port configurations, simultaneous flow to more than one port is also possible.
Figure 2. Some common types of multiport plug valves
Plug valves can be manually actuated but also can actuated by electric, pneumatic, hydraulic or with some other type of the actuator.
Application
Plug valve typically serve in on-off operations, particularly where frequent operation of the valve is necessary. These valves are not normally recommended for throttling service because, like the gate valve, a high percentage of flow change occurs near shutoff at high velocity. Valves having standard round port, are only used where restriction of flow is unimportant. For throttling service, a diamond-shaped port plug valves are used, thanks to its venturi restricted flow type design.
The most common fluids controlled by plug valves are gases and liquid hydrocarbons. Some water lines have these valves, provided that lubricant contamination is not a serious hazard for some applications. Plug valves, can also be used, in special applications such as throttling control in slurry service.
Plug Valve use in filed
Pros and cons
In general these valves are quick to turn off, smaller in size compared to most valves and have a minimal flow resistance. However, they can have a reduced port due to tapered plugs and can require a large force to actuate, due to high friction.
The use of a multi-port valve, depending upon the number of ports in the plug valve, eliminates the need of as many as four conventional shutoff valves and also eliminate much of the pipe fittings.
A disadvantage is that many multi-port valve configurations do not completely shut off flow. The accumulation of sediment and scale in the valve is prevented by the straight passage through the port and the wiping action of the plug as it is rotated 90 degrees. A disadvantage of the lubricated plug valve is the constant maintenance; lubrication is required at all times to maintain a tight seal between the body and plug. When installing plug valves, care should be taken to allow room for the operation of the handle, lever, or wrench. The manual operator is usually longer than the valve, and it rotates to a position parallel to the pipe from a position 90 degrees to the pipe. Like the gate valve, a plug valve has an unobstructed flow, yet requires only a 90 degrees turn to open it.
Stem corrosion is minimal because there are no screw threads.
When compared to the ball valves, plug valves are available in much larger sizes and are highly suitable for use in wastewater plants.
Do you know?
The plug valve is most probably the oldest type of valve in use today. Plug valves were in existence approximately 2,000 years ago and they were used in the ancient water systems of Rome.
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@wfecn.com or direct call +86 (577) 5775 5599.
