As far as I know there are Lubricated Plug Valves & Nun-Lubricated Plug Valves.

According to my short experience Non-Lubricated Plug Valves are mainly used in process industries like petrochemical or refining & Lubricated Plug Valves are used in Crude Oil Pipelines.

Nonlubricated plug valves are used in Chemical and process services.  They actually ARE lubricated: The plug rides in a PTFE sleeve or liner.  

Lubricated plug valves are used in applications where the lubricant will not render the process contaminated.  Mining, gas, petroleum are reasonably typical.  To cycle a nonlubricated plug valve, it is appropriate to first exercise the lubricator, forcing sealant between the plug and the body.  This "floats" the plug clear of the body so it can be turned.  Sealant (frequently called "grease" is specially formulated for the intended application, and the sealant selected should not be washed away nor react with the process fluid.

Take a look at the Flowserve.com website under "Durco" for nonlubricated plug valves and for "Nordstrom" for Lubed valves.  

The petroleum refinery I worked at uses lubricated valves, plug or otherwise.  However, they are bad-mouthed because the "don't work."  The irony is that they don't work because nobody lubricates them, properly if at all.

Too much or not enough grease can cause problems and we could never get the operations & maintenance folks to do the right thing, even with training.  Debating union job duties came into play.

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