Construction of the stop valve

The design of a shut-off valve is considered using the example of the most common type with a threaded connection to the pipeline, a pass-through body, a gland seal of the stem, and a disk gate.

A pass-through hole is made in the cast-iron body in a plane parallel to the axis of the pipeline, and a threaded stem with a hinged flat gate is located on the axis of the hole.

Due to the fixed thread in the valve head, the rotation of the flywheel is converted into a translational movement of the stem. In the extreme upper position, the gate fully opens the pass-through cross-section, and in the extreme lower position, it completely closes it. The stem seal is pressed by a bushing in the valve head.

Stem seal

Gland seals require periodic tightening and replacement of the gland, and leaks along the stem are possible during operation.

The design of a shut-off valve with a bellows stem seal is more complex than with a gland seal, and accordingly, the price is higher, but they provide complete tightness of the seal and do not require technical maintenance. The bellows seal is made of alloyed stainless steel.

Body

The shut-off valve body is made of brass, cast iron, steel, or stainless steel.

Cast iron valves are suitable for solving most general-purpose tasks, they are cheap and repairable, but they are subject to corrosion. Cast iron shut-off valves are installed in heating and hot water supply systems, as well as on drainage and air release pipelines.

Brass valves are installed in heating, cold and hot water supply systems, they allow the use of drinking water quality and are not subject to corrosion, but their price is somewhat higher than that of cast iron shut-off valves.

Stainless steel shut-off valves are used in the food and chemical industries in pipeline sections with aggressive environments.

In the basic design, the connecting flanges are located on the same axis, but there are modifications with connecting flanges located at a 90° angle.

Valve Stem

The stem can be perpendicular to the pipeline axis, as in the example mentioned above, or it can be inclined. Shut-off valves with an inclined stem are called 'angled'. The flow capacity (Kvs) of angled shut-off valves is higher than the flow capacity of straight valves of the same diameter.

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