A plug is a rotating manual valve. Uses a cylindrical or conical plug (plug-shaped disc) to allow or prevent direct flow through the body. Valve plugs provide a direct passage through the ports so that the fluid can pass through the valve with minimal turbulence. The flow can be fully open or fully closed in both directions.
Plug valves are used in many different liquid services. They perform well in slurry applications. They are used in on / off milk valves, even with very little leakage. They are used in air, gas and steam services, natural gas and oil piping systems, food processing, non-abrasive slurry, vacuum, pharmaceutical and vacuum services for high pressure applications. They are suitable for on / off. Initially, plug-in valves were designed to replace gate valves because plug-valve valves with their quarter-turn function can be easily opened and closed against flow compared to gate valves.
Plug valves are usually preferred for low pressure and low temperature services. Valves coated with materials such as polytetrafluoroethylene (PTFE) can be used for corrosive chemical services.
Special designs are required to handle abrasive and sticky liquids. Plug valves are usually found in sizes up to 18 inches (DN 450) and in low pressure classes [ANSI 150 and 300 classes (PN 16 and 40)]. In this article, we will review the parts, working principle, types, symbol, advantages and disadvantages of valve plugs. For more information, you can refer to the article related to valve control .
Components of a plug valve
Plug valves have all the common components such as stem, body, disc and bond. This disc is different from other valves due to the plug design.
Plug body valve
The body of the valve plug has all the internal components of the valve. The body is connected to the pipes through an end connection.
I am a plug-in valve
The valve stem connects the plug (or disc) to the stimulus. This helps to move the stimulus to the plug and thus opens or closes the valve plug. The plug plug has a small stem that attaches to the disc.
Figure 1: Parts of a plug valve
Plug-in disk valve
The plug-in disk, also known as the conical disk, acts as a plug, thus distinguishing between a plug and a globe. Of all the valves, plug plugs, ball valves and globe valves have similarities. The main difference is in the appearance of the disk. The globe valve has a cylindrical disc. The valve plug has a solid metal piece with a tapered end.
Plug ports valve
An important feature of a plug-in is its easy compatibility with the multi-port structure. In general, multi-port plug-in valves are widely used. They offer various benefits such as:
- Simple plumbing and installation
- Easier operation than a few gate valves.
- Remove expensive pipe fittings.
Depending on the number of valve ports, a multi-port valve can eliminate four normal shut-off valves.
The plug-in has the following port patterns:
- Round opening : It has round ports in two branches and a body.
- Rectangular opening : It has rectangular doors from the complete part of the hole.
- Standard opening : In this case, the area is even less than the standard pipe area.
- Diamond mouth : It has a diamond-shaped mouth through milk.
- Multi-port : Used with three or more pipe connections for service delivery.
- Radius design : With the opening of the plug in the body, the opening of the area is reduced.
The principle of the plug valve
The plug plug consists of a body with a conical or parallel seat in which a plug is inserted. The plug is formed with a port, the position of the port controls the amount of opening through the valve. Ports are known as openings in the valve body through which fluid can enter or leave. The plug fully opens or closes the 90 degree fluid flow. The plug is not as efficient as the ball valves and can only operate completely open or closed.
When the opening of the plug corresponds to the inputs and outputs, the flow continues through the valve. The pressure drop occurs through the reduced area of the plug port. However, with a full surface cylindrical plug, the pressure drop is minimal.
When the manual operator is in full rotation (90 degrees), the fork opening is perpendicular to the flow current and the edges of the fork rotate through the sealing device (sleeve, lubricant, etc.). When the complete rotation is about a quarter turn, the port is perfectly perpendicular to the current, creating a complete.
In gas pressure situations, where the plug is in the middle position, the fork doubles the pressure drop. The inlet flow area is reduced by turning the plug from the full port position, causing a pressure drop at that point. The current then enters the full port area inside the plug, where the pressure is retrieved, followed by another restriction on the output port. Leakage through the seat is prevented by squeezing the plug on the sleeve or other sealing mechanism, while packing prevents leakage through the stem.
With three-way valve settings that require current deflection, current enters the input and travels through the plug, which directs the current to one of the other two outputs. When the plug is moved 90 degrees, the current is routed to another output. In the middle position, the current may be diverted equally to both outputs. By combining current, current is directed from two inputs to a single output. For some of these arrangements to occur, you must rotate the plug a quarter-turn, half-turn (180 degrees) instead of the normal operation. With larger plug plug sizes [3 inches (DN 80) or larger], the torque required to break the seal may be somewhat excessive. This is due to more surface contact between the plug and the sealing device, as well as unfavorable operating conditions, such as high process pressure, high temperature, corrosion deposits, and so on. In this case, the hand levers are usually replaced by gear carts. , Which significantly reduces the torque requirement. The plug is suitable for low pressure and low temperature applications and is made in large sizes of 250 to 300 mm. The main limitation of the plug valve is that if large changes are made in the fluid temperature, differential expansion is inevitable, leading to unreasonable stiffness of operation or loss of pressure. The plug may be tapered, parallel and simple or lubricated. Another variation is known as a ball valve, in which the plug is spherical and has circular valves that rotate between concave circular seats. The main limitation of the plug valve is that if large changes are made in the fluid temperature, differential expansion is inevitable, leading to unreasonable stiffness of operation or loss of pressure. The plug may be tapered, parallel and simple or lubricated. Another variation is known as a ball valve, in which the plug is spherical and has circular valves that rotate between concave circular seats. The main limitation of the plug valve is that if large changes are made in the fluid temperature, differential expansion is inevitable, leading to unreasonable stiffness of operation or loss of pressure. The plug may be tapered, parallel and simple or lubricated. Another variation is known as a ball valve, in which the plug is spherical and has circular valves that rotate between concave circular seats.
Types of plugs valve
In general, there are four types of plug-ins. They are:
- Lubricated Plug Valve
- Non-lubricated Plug Valve
- Eccentric Plug Valve
- Expanding Plug Valve
Lubricated Plug Valves:
These valves use lubricants or sealants to facilitate their operation in a wide range of working pressures. The lubricant used between the plug and the body creates a seal and requires periodic lubrication injections. The sealant must be such that it does not wash off with the liquid as the liquid can become contaminated and must be able to withstand the temperature of the line. These lubricants are in the plug of most plastic sealants. The use of effective sealants with properties such as proper traction, resistance to chemicals and the ability to create impermeable seals around any part of the body is essential. The lubricating layer also protects the metal surfaces between the plug and the body from corrosion.
Lubricant plugs are produced in different sizes from 15 DN to 900 DN. They are used in applications with a pressure of more than 2500 psi.
Figure 2: Lubricated plugs for non-lubricated valves
Non-lubricated Plug Valve
These valves are commonly used for low pressure lines. These valves have a body liner or elastomeric sleeve that is installed in the body cavity. The conical and polished plug acts like a wedge and tends to press the sleeve into the body. Thus the sleeve reduces the friction between the plug and the body.
There are three types of non-lubricating plugs:
- Lift-type plug valve
- Elastomer sleeved plug valve
- Fully lined plug valve
The Lift-type plug valve provides a mechanical way to separate the tapered plug from the seat surface for easy rotation. Lifting can be done with an external lever.
The elastomer sleeve valve plug has an elastomer sleeve. This is a TFFE sleeve that completely surrounds the plug. The elastomer sleeve is engaged through the metal body and locked in place. This sleeve has a lower coefficient of friction and is also lubricated.
Coated valve plug : In this type of valves, a cheap cast iron body is used. The body and plug of the milk are completely covered with Teflon so that the milk has the ability to resist corrosive liquids using iron as the body.
Eccentric Plug Valve
In this type of plug design, even a half plug is used. This design helps in applications that require more sitting force with minimal friction from open to closed position. Off-center plug-ins are used in a wide range of flow control and separation services. Some common uses for off-center plugs include clean and dirty water, sewage, sludge, air, and other services.
Expanding Plug Valve
Plug-ins are drawn in a complex design. They use multiple components that allow the valve plug to expand mechanically, giving it a double-build function in a single valve. These types of valves use a mechanism that rotates between the open and closed positions and protects both seals from the flow path. The body and the seal do not contact each other during rotation, which prevents wear and tear of the seal. For applications that do not require double separation, plug valves are often used to prevent product contamination.
Types of plug-ins based on the template
According to the patterns, plug plugs are classified as follows:
- Round opening – full round ports on the plug and body.
- Rectangular opening with rectangular ports of the complete part of the hole.
- Standard opening where the valve area is less than the standard pipe area.
- Lozenge port whose opening is in the shape of a rhombus through the valve.
- Multiple ports with three or more pipe connections.
- Radius design by reducing the transmission area and having a radius flow in the body.
- Short valve plugs with area reduction ports and face-to-face dimensions
Plug valve material
Plug valves can be made of different materials. Both metal and plastic The most common materials of the plate are:
- stainless steel
- Plastic and so on
In P&ID, the following plug-in symbol is used to identify and distinguish it from other valves.
Figure 3: Plug valve symbol
The benefits of plug-in Valve
The main advantages of the valve are:
- It has a simple design and fewer parts
- Can be opened or closed quickly.
- This valve offers the least current resistance.
- The use of multi-port designs helps to reduce the number of valves required and allows a change in flow direction.
- Provides a reliable service against leakage.
- They are easy to clean, which can be done without removing the body from the piping system.
Disadvantages of plug plugs Valve
Limitations or drawbacks of a plugin include:
- To rotate the plug requires a lot of friction, which leads to more force to operate these valves.
- Larger valves require an actuator.
- The price of these valves is more than ball valves that have a similar design.
- The greater pressure drop is due to the reduction of the port.
As mentioned earlier, plug valves are suitable for a wide range of services such as air, gas, steam, grout, ore, sewage applications, oil piping systems, etc., for vacuum as well as high pressures. But it is usually used in low pressure and low temperature services. Most plug-ins are used:
- To control the directional flow, even in medium vacuum systems.
- For efficient management of gas and liquid fuels.
- For safe management of extreme temperature flow, such as boiler feed water, condensate and other such elements.
- To regulate the flow of liquids containing suspended solids such as slurry.
Rose Calibration Company in Melbourne, Australia with over ten years of experience provides all calibration, maintenance, and repair services throughout Australia. If you live in Sydney, Melbourne, Adelaide, Perth, Geelong, and Brisbane, you can receive your quote in less than two hours by fill-up the form via the “Booking” link.