Check valves are the most common type of valves used in industries. Although the basic function of a check valve is to prevent back flow of fluid but there are various types of designs which are used to manufacture check valves. Each valve is made of different material to make it suitable for use in different industries.
Check valves are crucial part of any pipeline, especially in industries like petrochemical where a malfunctioning check valve might mean loss of fluid and money too. Therefore, check valves must facilitate smooth flow; a low pressure self-sealing valve will be more effective in preventing the loss of fluid; and can be mounted in horizontal or vertical pipeline.
Check Valves have many categories and it sometimes becomes confusing to decide which one will be the best fit. Further, each valve type is divided into sub categories depending upon the structure used in them to prevent the back flow.
For example Wafer check valves that are designed as an alternative to lift check valves can be divided into swing check valves and butterfly check valves. Swing wafer check valves have a flap that opens up with the inlet pressure; these valves are mostly used in industries where large size pipelines are used to transport fluids.
Types of check valve designs are as follows:
Ball or gravity check valve: These valves mostly have spring loaded metallic balls that shut down completely once the inflow stops and minimum reverse pressure is required. In the ball type valves where there is no spring, high reverse pressure is required to bring the ball back into is seat and obstruct any back flow.
Lift check valves: In lift check valves the plug is automatically operated. The plug is in cone shape that lifts when the in-flow takes place and comes back to its static position later.
Diaphragm style: This type of valve has a diaphragm as the element to allow or stop the flow of fluid. Pressure differential is essential to make this valve work. The inflow pressure has to be more than the outflow to move the rubber diaphragm and displace it from its seat and allow the flow.
Wing style: This is another type of check valve that can be used in pipelines where the pressures are low. The plates swing easily to open up or shut down in low pressure conditions.
Tilting Check Valve: In tilting check valve adisc that rotates to and fro on a hinge, which tilts to allow the flow and then fits back to stop the flow of fluid through the pipeline.
Stop Check Valve: Stop check valves are applied in those pipelines where it may be required to completely block the flow irrespective of the pressure differential in upstream and downstream segments. Unlike other check valves the function of this valve can be controlled by external mechanisms.
Regardless of the type of designs that check valve is made of, each one of them follows API 6D standard. Any valve design must be complaint with API 6D though at times some industries may use valves based on API600, 602, 608 or 609.
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