One of the popular types of pipeline shut-off and safety valves is a check valve. It is installed in various technological systems and is designed to prevent the reverse flow of the working medium during the occurrence of any emergency situations. For example, a sudden shutdown of a pumping unit, as a result of which the liquid begins to move under pressure in the backward direction, which in turn can lead to the failure of expensive equipment. In addition, the device will come in handy when the pipeline breaks. Indeed, after its closure, the leakage of the substance will be minimal.

The principle of operation and examples of use

The non-return valve operates on the principle of blocking the flow hole with a locking mechanism under the influence of the return pressure of the conveyed medium. In this case, if the substance moves in the required direction, the shutter remains open, and it closes only when it moves in the opposite direction. Such devices are in great demand in many areas of industry and economic activity, among which the following can be highlighted:

• oil and gas complex;
• chemical industry;
• heat and power sector ;
• food industry.

Such devices are needed in district heating and water supply networks. They are also installed in sewer lines that transfer wastewater to treatment systems.

Varieties by type of locking device

By this criterion, check valves are presented in several main categories:

• Ball. The locking mechanism is a spherical body pressed against the seat by a spring.
• Rotary. A kind of damper is installed in the body of the device, which, when the substance flows back, goes into a closed position.
• Lifting. The function of the shut-off device is similar to the valve, only it opens when the liquid or gas moves in the right direction, and in the case of a return stroke, it is pressed tightly against the seat of the body.
• Double-leaf. In the design of the shut-off unit, there are two flaps located on the same axis passing through the center of the through hole. In the open state, they are folded, and when the movement of the substance stops, they open.
• Disk. A flat plate mounted on a spring-loaded rod acts as a working element in them. With normal pressure, it is squeezed out, which contributes to the free passage of the substance, and when this indicator decreases, it is relocated to the closed position.

The choice of one or another option directly depends on many factors, among which one can name the established pressure, the degree of contamination of the environment, the temperature regime of operation, etc.

Classification according to the material of manufacture and method of installation

Various materials can be used for the production of check valves. In this case, the main condition is their ability to withstand the negative effects of such factors as high or low temperatures, the level of aggressiveness of the reagent, and service life. The most popular are carbon and alloy steels, stainless steel, brass. According to the method of installation in the pipeline, protective fittings can be welded, socketed, flanged and interflange.

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