PLUG VALVES

The simplest and most common general type of plug valve 

Has two positions, open to allow flow, and shut (closed) to stop flow.

Ports are openings in the valve body through which fluid can enter or leave

The plug in this kind of valve has one passageway going through it

The ports are typically at opposite ends of the body; therefore, the plug is rotated a quarter of a full turn to change from open to shut positions.

This makes this kind of plug valve a quarter-turn valve

There is often a mechanism limiting motion of the handle to a quarter turn, but not in glass stopcocks.

Flow from one port could be directed to either the second or third port.

A 3-way plug valve could also be designed to shift flow between ports 1 and 2, 2 and 3, or 1 and 3, and possibly even connect all three ports together

The flow-directing possibilities in multi-port plug valves are similar to the possibilities in corresponding multi-port ball valves corresponding multi-port valves with a rotor

An additional possibility in plug valves is to have one port on one side of the plug valve and two ports on the other side, with two diagonal and parallel fluid pathways inside the plug

In this case the plug can be rotated 180° to connect the port on the one side to either of the two ports on the other side.