API 6D plug valves feature a cylindrical or conical disc with one or more horizontal hollow passageways that can rotate to control the flow of fluid through the valve. Types with an open and close position are the most common two-port lubricating types.
How Do Plug Valves Work?
It is composed of a cylindrical or conic disc that controls the flow of fluid, opening and closing the passageway between opposing ports. On top of the mechanism is a lever that controls the valve.
Among the liquids and gases that can be handled by these valves are:
- Liquids that are neutral, such as oil and water
- Liquids that are acidic or alkaline (corrosive)
- The slurry
- Neutral gases, such as air and steam
- Corrosive gases, such as chlorine and acid vapors
- Plug valves come with the flanged, hub, or buttweld ends and can be cast (> inches) or forged (up to 2 inches diameter).
API 6D (downstream) and API 6A (upstream) are the two most important references for this type of valve in petrochemical applications.
A plug valve can be operated with a wrench or gear, or it can be actuated with electric, electrohydraulic, pneumatic, and gas over oil actuators.
Plug Valve Types
In general, plug valves come in four main types, each with its own advantages and disadvantages.
Lubricated Plug Valve
The lubricant in lubricated plug valves reduces friction and tightly seals the ports. As a lubricant, usually a base oil which improves the viscosity of the moving parts. Such as amorphous or fumed silica, which inserts between the plug face and the body seat at high pressure.
For some applications, manufacturers recommend using a lubricant matched to the process fluid, as well as resealing the valve after a certain number of cycles (or every cycle in some applications).
Because of this maintenance requirement, lubricated valves are used in applications that do not operate continuously. These types of valves are suitable for processes containing mildly abrasive particles such as upstream applications, gas pipelines with by-pass valves, and blow-down valves at valve stations.
Generally, metal seats employ in this type of plug device.
Non-Lubricated Plug Valve
A conical or tapered disc acts as a wedge and presses a sleeve (that reduces friction between the plug mechanism and the body cavity) against the body cavity.
When low maintenance is the priority, such as in sulfur, hydrogen fluoride. When fluids could solidify and block valves, non-lubricated valves are preferred.
Due to the non-metallic seats they use, non-lubricated valves can only be used in specific applications when it comes to temperatures, pressures, and types of transferring fluids (chemical resistance).
These valves can be divided into three types: fully lined, elastomer sleeve, and plug-type lift valves.
Eccentric Type
Half plugs are a key feature of eccentric valves that offer benefits such as stronger seating forces and reduced friction between the open and closed positions.
Comparatively to the concentric design, eccentric valves show improved shutoff capabilities.
Typical applications for this kind of plug valve include dirty water, sewage, sludge and slurries, air, and other similar services that require tight shut off.
Double Expanding (Double Block and Bleed – DBB)
In terms of design, this is the most complex plug valve, as it has multiple components that allow the valve to expand mechanically in order to achieve a true double block and bleed mechanism.
In applications that do not require double isolation. They commonly use to prevent product contamination.
An expanding valve utilizes to protect both seals from the flow path by rotating between open and close positions. When the valve is closed, the slips expand onto the body seat to prevent the seals from being worn or abraded during rotation.
Short vs. Long Pattern
Plug valves come in three different designs.
There are approximately 40% to 60% fewer ports in a short pattern design than a full-bore design
With a longer face-to-face dimension and a port area of 50-70% of the full-bore plug valve. The regular pattern design to minimize flow loss.
The full bore design has a long face-to-face dimension and an oval port (Venturi).
The last configuration allows unrestricted flow and pigging of the pipeline. The basic design of modern plug valves originated in the Roman Empire.
Plug valves use to control the flow of the medium. They utilize it for isolation, shutting off the flow, and for on/off purposes.
Tubing plug valves using for a wide range of applications like oil, chemical, and water, etc.
Plug valve advantages are listed below:
- Easy to use
- Cost-efficient
- Made from quality materials
- Easy to install
This Plug valve can also utilize for isolation, temperature control, shut off, on/off control.
Also, Read Plumbing Tools That You Can Keep At Home!
The Plug Valve Vs Ball Valve
A Plug valve and a ball valve typically perform the same function (fluid shutoff). However, they differ in the following ways:
- As a general rule, plugIn general, plug valves are more economical than ball valves because they are simpler to design.
- Comparing plug valves to ball valves (an issue often encountered with ball valves. Because of the space between the sphere and the body of the valve), plug valves are less likely to collect dirt in the interstitial spaces.
- The maintenance requirement for ball valves is higher than that for plug valves, especially after a planned or unplanned plant shutdown.
- Plug valves have full ports, so there is no pressure drop, whereas ball valves have reduced or full ports. (a full port ball valve would be much heavier and bulkier than a plug valve of the same size).
Plug valves are a great substitute for ball valves, despite the fact that ball valves are still considered industry standards for shut-off operations, at least in the oil & gas industry.
Conclusion
Plug Valve is a device that is use in industrial applications. It is also use in water treatment, food and beverage, chemical processing, and other applications. The main principle of a plug valve is to control the flow of material by plugging the passage. This device utilizes various industries and is cost-effective.
