Our natural gas suppliers used plug valves on the gas lines -- they have started to use some ball valves, but still have many plug valves -- we used plug valves on gas valves on the boiler (many are still hand operated) -- I assume they were used for a) ¼ turn, easy to operate, b) full bore, small dp, c) squirt of grease now and then kept them working and sealing, minimum maintenance, few parts...
Plug valves are quarter turn, positive shut off valves closely related to ball valves.
Plug valves were the one of the first types of valves made (and used typically by the brewers in making beer)Ancient plug valves were originally made from wood....
Plug valves are typically very inexpensive and suitable where they are not operated frequently ( such as in natural gas service)
MJC
"There comes a time in the affairs of man when he must take the bull by the tail and face the situation." W.C. Fields
plug valves seal off by the use of thick plug valve grease between the plug and seats. sense grease is the main seal, the valve is very dependable when greased before use.
Plug valves were used on some slurry pipeline service although these days hard faced ball valves are more common.
Eccentric plug valves are used on control valve applications where the fluid carries solids. They give a far better control range than a butterfly valve. Also any wear is taken up in the degree of actuation.
Refer Pegler or Dezurik websites for more details.