Plug Valve

Plug valves are valves with round or conically tapered “plugs” which may be rotated within the valve body to manage flow with the valve. The plugs in plug valves have a number of hollow passageways going sideways with the plug, to ensure that fluid can flow with the plug once the valve is open.
Plug valves are pretty straight forward and frequently economical.Once the plug is conically tapered, the stem/handle is usually connected to the bigger diameter finish from the plug. Plug valves tend not to have bonnets but frequently possess the finish from the plug using the handle uncovered or mostly uncovered towards the outdoors. In such instances, there’s not often a stem. The stem and take care of frequently come successfully, frequently an easy, roughly L-formed handle connected to the finish from the plug. Another finish from the plug is frequently uncovered towards the outdoors from the valve too, however with a mechanism that maintains the plug in your body.
The easiest and many common general kind of plug valve is really a 2-port valve with two positions: available to allow flow, and shut (closed) to prevent flow. Ports are openings within the valve body by which fluid can enter or leave. The plug in this sort of valve has one passageway dealing with it. The ports are usually at opposite ends from the body therefore, the plug is rotated a 4th of the full use vary from available to shut positions. This will make this sort of plug valve one fourth-turn valve. There’s frequently a mechanism restricting motion from the handle to some quarter turn, although not in glass stopcocks.Slightly conically tapered metal (frequently brass) plug valves are frequently utilized as simple shut-off valves in household gas lines.It’s also feasible for a plug valve to possess greater than two ports. Inside a 3-way plug valve, flow in one port might be forwarded to either the 2nd or third port. A 3-way plug valve may be made to shift flow between ports 1 and a pair of, 2 and three, or one and three, and perhaps even connect the 3 ports together.
The flow-directing options in multi-port plug valves are the same options in corresponding multi-port ball valves or corresponding multi-port valves having a rotor. Yet another possibility in plug valves may be the get one port somewhere from the plug valve and 2 ports on the other hand, with two diagonal and parallel fluid pathways within the plug. Within this situation the plug could be rotated 180° for connecting the main harbour around the one for reds either to of these two ports on the other hand.

• Standard: API, DIN, JIS, GB, ANSI.
• Material: Stainless Steel, Carbon Steel, Brass, Bronze, Alloy Steel, Titanium, 904l, Ductile Iron, Cast Iron, Cast Steel. 
• Size: 1/2″ ~24″, DN15~DN600.
• Pressure: 150LB~1500LB, PN10~PN320. 
• Type: Threaded, Lubricated, Sleeved, Lined, 3 Way, Lift, Double Block & Bleed, Full Port, Eccentric, Metal Seated, PTFE Seated, Pressure Balanced, Flanged, Steam Jacketed, Cryogenic, Low Tempreature, Moterized, Pneumatic.

Plug Valve Parts

Typical plug valve is consisting of body, bonnet, stem and plug. The seat is an integral part of the body in case of lubricated plug valve. For non-lubricated plug valve, a non-metallic seat is used to improve leak tightness of the valve.

Image- DOE Handbook

Plug valve disk: Plugs are either round or taper cylinder. They may have various types of port openings, each with a varying degree of the opening area.

Plugs are available with

• Rectangular Port
• Round Port and
• Diamond Port

Here in the image, you can see the taper plug with Rectangular, Round, and Diamond Port design.

• Rectangular Port is the most common for plug valve. The rectangular port represents at least 70% of the corresponding pipe’s cross-sectional area.
• Round port plug has a round opening through the plug. It is available in full bore and reduced bore design. Valves with reduced ports are used only where restriction of flow is not important.
• Diamond Port plug has a diamond-shaped port through the plug. All diamond port valves are venturi restricted flow type. This design is for throttling service.

Types of Plug Valves

Plug valves are available in either a lubricated or non-lubricated design and with different styles of port openings through the plug.

Lubricated Plug Valve

The plug in a lubricated plug valve has a cavity in the middle along its axis. You can see this in the image. Lubricant chamber at the bottom and the sealant injection fitting at the top ensure the supply of lubricant.

Small check valve below the injection fitting prevents the sealant from flowing in the reverse direction once the sealant is injected into the cavity.

Plug surface gets constantly lubricated by the sealant that moves from the center cavity through radial holes into lubricant grooves on the plug surface. Now why we required all this? Many plug valves are of all metal construction.

The narrow gap around the plug may allow leakage, and if you reduce the gap further, it will increase the friction and plug may get stuck inside the valve body.

Image – Serck Audco, Newport

The lubricant reduces the force required to open or close the valve and allows smooth movement of the plug. The lubricant also prevents corrosion of the plug.

The lubricant material must be compatible with the fluid of the pipeline. It should not dissolve or wash away by the flow medium as this could contaminate the fluid, and damage the seal between the plug and the body, resulting in leakage. Also, the sealant used must be able to withstand a temperature of the flow medium.

Lubricated plug valves are available in the large size range, and they are fit to work in high-pressure temperature services. These valves are subject to less wear and provide better corrosion resistance in some service environments.

Non-lubricated Plug Valves

A non-metallic elastomeric sleeve or liner is used in this type of plug valve. This sleeve is installed in the body cavity of the valve. The polished tapered plug acts as a wedge and presses the sleeve against the body.

This nonmetallic sleeve reduces the friction between the plug and the valve body. Non-lubricating plug valves required minimum maintenance. Due to the non-metallic seat, these valves are not used in high-temperature services.

Lubricating and non-lubricating plug valves are capable of providing a bubble-tight shutoff and are of compact size.

Multi-Port Plug Valves

Here you can see the 3-way multiport plug valve. The top image is of 3-way 3-port design and bottom is 3-way 2-port design.

This is 4-way design.

Multiport valves are used in transfer lines and for diverting services. A single multiport valve may serve the purpose of three or four gate valves or other types of the shutoff valve. However, sometime multiport valve does not completely shut off flow. Great care should be taken in specifying the particular port arrangement for proper operation.

Plug Valve Application

• Plug valve used as on-off stop valves and capable of providing bubble-tight shutoff.
• It can be used in different types of fluid services such as Air, gaseous, vapor, Hydrocarbon, slurries, mud, and sewage applications.
• Plug valve can be used in a vacuum to high-pressure & temperature applications

Plug Valve Advantages

• Simple design with few parts
• Quick to open or close
• inline maintenance possible
• Offers minimal resistance to flow
• Provides reliable leak-tight service
• Multiple port design helps reduce the number of valves needed and permits a change in flow direction

Disadvantages of Plug Valve

• It requires greater force to operate, due to high friction
• Larger valves cannot be operated manually and required an actuator
• Pressure drop due to reducing port
• Cost of Plug valves may be more than ball valves for given size and class.