Plug valves are valves with cylindrical or conically tapering "plug" which can be rotated inside the valve body to control flow through the valve. The plugs in plug valves have one or more hollow passages running sideways through the plug, so that fluid can flow through the plug when the valve is open. Plug valves are simple and often economical.
The simplest and most common general type of plug valve is a two-way valve with two positions, open to allow flow in and closed (closed) to stop the flow. Ports are openings in the valve body fluid can enter or leave. The plug of this type of valve has a passage which passes through it. The ports are typically at the opposite ends of the body, and therefore the plug is rotated a quarter of a full turn to change from open to closed position. This makes this type of plug valve a quarter turn valve. There is often a mechanism to limit movement of the handle to a quarter turn, but not the glass cranes.