Lubricated plug valves use a lubricant (base oil and viscosity improver), injected into the valve under pressure to reduce friction and to provide a seal between the valve’s seating surfaces. Lubricated plug valves are high maintenance as they need to be lubricated regularly. They are therefore recommended for applications with infrequent operations. While the plug is mostly cylindrical, they are also available in conical shapes.

Unlike  non-lubricated plug valves, Lubricated plug valves are designed with grooves in the plug that retain a lubricant. When in use, the lubricant prevents sticking and provides a hydraulic force that helps lift the plug and reduce the effort required for rotary operation. Additionally, the lubricant provides the seal between the seating surfaces of the valve body and plug so that a tight shutoff can be achieved.