College of Product Knowledge: GENERAL APPLICATION VALVES PART III
In this final installment on the subject of valves, we'll look at several other common designs used in our industry today.
Construction: The two basic approaches to plug valve design are called the "lubricated" and "non-lubricated" types. It is important to understand that the term "lubricated" in this case refers to a means of sealing the plug against leaking. Filling grooves on the plug with a viscous lubricant (sometimes called "sealant") provides a leakproof seal in the area between the plug and valve body, also assuring smooth and easy operation. Non-lubricated plug valves, on the other hand, do not use such a means of sealing, typically using "O" rings instead. There are two common ways to achieve sealing of the passage in a plug valve using a non-lubricated approach. The first involves a design in which the plug is allowed to wedge tightly into its mating cavity when rotated into the "off" position (thus providing a tight seal), and is made to lift slightly when turned on (to relieve binding). The other approach uses an elastomeric (resilient) sleeve around the plug, or the surface of the plug itself in a resilient material.