from Wikipedia, the free encyclopedia
A stopcock ( plug cock ) on a machine

The shut-off valve is a fitting that completely opens or completely blocks the flow of a fluid in a pipeline . A tap is operated by turning the closing element 90 °. The construction of stopcocks is completely tight ; this applies to both the connected pipeline and the actuator spindle .

In contrast to the shut-off valve , in which the flow can be continuously adjusted as required, shut-off cocks are not intended to be set to intermediate positions. They are usually only operated in two states: fully open or closed.

In plumbing and heating technology, valves are mostly used for water , even if they are often referred to as a tap ( faucet ). Stop cocks are required for gas. Stop cocks are suitable for the smallest to large nominal sizes and nominal pressure levels . They have the advantage of being tight for the pipeline to be shut off and only emitting the smallest amounts of leakage into the environment. They are therefore well suited for toxic, flammable or other hazardous fluids. They also have a low flow resistance . However, their reliable function is very limited by contamination of the fluid. They cannot control (throttle) the fluid flow, and their space requirement in a pipeline is comparatively large.

When the shut-off valve is closed, a small part of the medium remains in the bore of the closing element.

A tap is not built into a pipeline, controls the leakage from a container and is also a stopcock.


Stop cocks differ in the design of the closing element:

Chick cock
The frustoconical closing element ( plug ) sits as an extension on the axis of rotation, in the cone there is a rectangular or trapezoidal hole at right angles to the axis of rotation.
Ball valve
A pierced ball serves as a closing element. Ball valves can be used at very high pressures because of their precisely fitting sealing seat.
Piston cock
A cylinder piston closes the inlet.
Cylinder valve
A pierced cylinder serves as a closing element.

A distinction is made between fittings with full and reduced passage. In special fittings, a shut-off valve can take on more than just one switching position, so that this fitting is suitable for distributing and combining fluid flows. This arrangement is also called a multi- way valve , for example a three-way valve .

Individual evidence

  1. Data sheet of a cylinder valve (PDF; 148 kB), archived from the original - accessed on November 30, 2018