Check valves are employed in wide range of piping used to transport fluids, or keep the gases or fluids in the piping separate. These valves allow the release of content only in one direction. At times Check valves don’t have external handle to make them work, they work automatically on the basis on internal pressure.

Since they are used in different types of industries they are manufactured in carbon steel, alloy steel or stainless steel. Depend on size Check valves are necessary pieces in the piping. Although Check valves are designed on the basic API 6D standard but, for different industries they are further customized according to API 608,609,602, or 600 criteria.

The most important criteria to be considered in installing a check valve in a piping is the Cracking pressure. This is the pressure that opens the valves and thus choosing the right fit check valve for the piping is crucial. Check valves are used where there is need to:

• Prevent the reverse flow of contents of fluids or gases present in the pipe system

• Shield the other components of pipeline from the damage by blocking any back flow.

• Thwart the flow because of gravity or pressure variations

Broadly speaking there are following types of check valves:

Stop check valve: This type of check valve is a designed to cut off the supply of the liquid, water, oil or gas irrespective of the direction of flow. Stop check valve can stop the flow of contents irrespective external pressure.

Ball check valves - It has a spherical metallic ball to cut-off the flow. It is used in pipe systems that carry gel or liquid contents. In some designs the ball is made up of ruby.

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Lift- check valve: The disc in this valve is lifted to facilitate the flow of fluid. The valve closes when the pressure recedes.

Diaphragm check valve: This valve has a flexible diaphragm that opens or closes depending upon the flow and pressure in the pipeline

Besides the above mentioned types there are various other designs of check valves and each type gives rise to a different category, for example bulky lift check valves can be replaced with wafer check valves.

Check valves are a huge category and are most frequently used in chemical, water,oil and gas, power, pulp and paper industry. They are also used in fire systems such as dry pipe fire sprinkler systems. In all the applications check valves thwart the backward flow of water or fluids into the piping system.

Thus, based on the industry requirement you can choose from wide variety of design specifications.