Three basic parts comprise the lubricated plug valve: body, cover and plug. The plug is the only movable member. The valve is opened by rotation only, the plug turning on a lubricated seat. While the plug is available in cylindrical and tapered form, the later is generally preferred, because the tapered rotary principle results in quick and simple valve operation. The conical shape of the plug combines the tight fit advantage of wedge action with the sliding action of rotary movement. Rotation eliminates the need for raising and lowering a movable valve member, and protects seating surfaces from exposure to corrosive elements.