Plug valve

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

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

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

Stopcocks used in laboratory glassware are typically forms of conically tapered plug valves.

When fused with the glassware, the valve bodies are made of glass.

When glass is used for both the stopcock body and the plug, the contacting surfaces between them are special ground glass surfaces (see Laboratory glassware) often with stopcock grease in between.