Lubricated Plug valve is critical components of a pipe system that transfers liquids, gases, vapors, slurries, and other substances from one location to another. When the media to be transferred contains slightly abrasive particles, mostly a Lubricated Plug Valve is used. It is a quarter-turn valve, which is beneficial for rapid and frequent operation.

Generally, a lubricated plug valve has a cylinder or cone type shape that is rotated inside the valve housing to control fluid flow. In addition, the plug valves are frequently positioned horizontally in one or more hollow passages that facilitate the flow of the valve while it is open. The 2-port design with a closed and open state is the most common design of the plug valve.

Now that you have a basic understanding of the lubricated plug valve, let’s find out in detail what is a lubricated plug valve classification, how does it work, its unique features, benefits, and applications.

Lubricated Plug Valve Classification?

1. Conventional oil lubricated plug valve

A. For conventional metal seat lubricated plug valve, the installation position of the plug cone is positive. In order to reduce the friction between the valve body and the sealing surface of the plug, the valve generally uses the sealing structure of the sealing grease lubrication seat. The high-pressure sealing oil injected from the high-pressure oil nozzle forms a high-pressure sealing ring around the plug, that is, there is a layer of oil film between the valve body and the sealing surface of the plug cone, which can be sealed and lubricated, and easy to open and close.

B. In order to further reduce the opening and closing torque of the lubricated plug valve, usually the method of reducing the diameter of the plug is used, therefore the lubricated plug valve usually uses a rectangular flow path. This method increases the fluid resistance of the plug valve while reducing the opening and closing torque of the plug valve.

C. The sealing part of the plug cone is welded with STL alloy material or adopts surface hardening technology to enhance the wear and corrosion resistance of the sealing surface, and the service life is long.

D. The surface of the cock cone is finely ground to the mirror surface, and the sealing surface of the valve body is ground, which has a lower opening and closing torque.

2. Pressure balanced lubricated plug valve

In order to reduce the torque of conventional metal seat lubricated plug valves, pressure balanced lubricated plug valves are often used. In addition to the characteristics of conventional oil ubricated plug valves, the pressure balanced plug valves also have the following characteristics:

A. The plug cone of the pressure balanced lubricated plug valve is mounted in an inverted position. There is a check valve on the upper part of the plug cone. When the valve is closed, due to the difference in the upper and lower cut area of the plug cone, the injected high-pressure sealing oil causes the plug body to be lifted upwardly, so that the plug body and the valve sealing surface can be better sealed.

B. At the moment when the valve is opened, the pressure in the lower chamber of the valve body is balanced with the medium pressure in the pipeline. The high-pressure sealing oil in the upper chamber causes the plug body to be pushed downward, and a slight gap appears between the plug cone and the sealing surface of the valve body, the torque of the rotating plug body is effectively reduced.

C. In high temperature conditions, the thermal expansion of the plug can be absorbed by its rise and fall. Oil lubricated plug valve, although the use of oil lubrication can appropriately reduce the opening and closing torque, but it may form pollution of the medium. Therefore, the sealed lubricant is selected for the actual operating conditions.

What Is A Lubricated Plug Valve?

In general, valve manufacturers suggest lubricants that are suited to the fluid process, and valves frequently have to reseal after just a few cycles and in certain circumstances after every cycle.

The tightly sealed seat with lubricating oil is meant to decrease friction between the valve body and the sealing surface of the plug. A layer of oil film between the valve body and the sealing surface of the plug cone confirms the tight seal and smoothens the open/close motion when high-pressure sealing oil is injected around the plug to form a high-pressure seal ring.

How Does A Lubricated Plug Valve Work?

The lubricant substance must be compatible with the pipeline fluid. It should not degrade or be washed away by the flow medium since this might pollute the fluid and break the seal between the plug and the body, leading to leakage. Furthermore, the sealant employed must be able to resist the flow medium’s temperature. 
 

Lubricants Used In A Plug Valve

As it offers a flexible and renewable seat, the lubricant effectively becomes a structural component of the valve. This removes the need for force fits and distortable-seat contacts to form a seal. However, to avoid the damaging effect of the line fluid and establish an unbreakable seal around each body port, the lubricant must demonstrate adequate flexibility and resistance to solvents and chemicals.

The lubrication layer also prevents corrosion on the metal surfaces between the plug and the body. The seal produced by the lubricant injected through a system of lubrication grooves circuiting each port assists in the maintenance of the necessary film on the metal, closing surfaces.

Features And Benefits Of Lubricated Plug Valve

Sealant supports in the formation of a renewing the seal between the plug and the body, preventing internal leaking. It also keeps the sitting surface from corroding. It also works as a lubricant, reducing the amount of force necessary to operate the valve. Lubricant pressure lifts the plug up from the seat for a brief period, making it easier to spin. Furthermore, the high pressure ensures that no sediments are trapped between the valve body and the plug.

Lubricants used in a plug valve are, in fact, plastic sealants. Therefore, it is critical to use an efficient sealant with qualities such as appropriate elasticity, tolerance from solvents and chemicals, and the capacity to establish an impermeable seal around each body component even when it’s under pressure. The lubrication layer also prevents corrosion on the metal surfaces between the plug and the body.

Lubricated plug valve is produced in a wide variety of sizes and are suitable for use in high-pressure & temperature services. They are available in different sizes ranging from half an inch to 24 inches in length and with pressure capacities of up to 6000 psi. They are available with steel or iron bodies. In some operating conditions, these valves are less prone to wear and provide superior corrosion resistance.

Lubricated Plug Valve Applications

These lubricated plug valve is considered to be high-maintenance plug valves; they are commonly employed in special applications. For example, lubricated plug valves work effectively in operations that use fluids containing slightly abrasive particles, such as polluted upstream applications, gas pipeline systems requiring bypass valves, and blow-down valves on valve stations and kicker valves.

Some industries where Lubricated Plug valve is used:

• Pulp & Paper, Mining, for metal works.
• Wastewater management, Midstream transportation, Downstream processing, etc.

• Lift-type plug valve.
• Elastomer sleeved plug valve.
• Fully lined plug valve.

This type of valve employs a non-metallic elastomeric sleeve or liner. This non-metallic sleeve reduces the friction between the plug and the valve body. Non-lubricating plug valves required less maintenance. Because of the non-metallic seat, these valves cannot be utilized in high-temperature applications.

Both lubricating and non-lubricating valves are capable of providing a bubble-tight cut-off and are small in size.