Lubricated plug valve consists of a cavity in the middle of plug along its axis. This cavity is closed at the bottom and fitted with a sealant-injection fitting at the top. The sealant is injected into the cavity, and a check valve below the injection fitting prevents the sealant from flowing in the reverse direction. The sealant oozes out from the center cavity through radial holes into lubricant grooves that extend along the length of the seating surface of the plug.

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

• 1.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.
• 2. 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.
• 3. 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.