A PLUG VALVE is a rotational motion valve used to stop or start fluid flow.   The name is derivedfrom the shape of the disk, which resembles a plug.The simplest form of a plug valve is the petcock. The body of a plug valve is machined to receive the tapered or cylindrical plug.  The disk is a solid plug with a bored passage at a right angle to the longitudinal axis of the plug. In the open position, the passage in the plug lines up with the inlet and outlet ports of the valve body.  When the plug is turned 90