Check Valves – What Are They, And How Do They Work?

Almost every industry uses check valves as one-way or non-return valves. Simple check valves prevent reverse flows, reducing damage and ensuring efficient operation. A reverse flow, for instance, can cause a water hammer. Often, the system and its connected pipes and valves are affected by repeated extreme pressure surges, which may result in rupture or damage to the system. The repeated impacts of the water hammer may eventually cause the system to fail, even if a failure doesn’t occur immediately. Let us know more about check valves.

Working Principle Of Check Valves

Check valves are a common component for fluid flow and pumping in many industries, including chemical processing, pulp, and paper production, food processing, wastewater treatment, industrial, mining, and marine applications like a floatable jet ski dock, pipelines, power generation, and heating and air conditioning.

Check valves have a single inlet and outlet and operate on differential pressure. As soon as the pressure in the upstream pipe reaches a certain level, the valve will open automatically. One of the main characteristics specified for all check valves is the cracking pressure, commonly known as the minimum operational pressure.

Design And Manufacturing

It is necessary to connect check valves in series to prevent the backflow of contaminated water into clean water lines. There are a variety of check valves available that use metals, polymers, and rubber for a variety of applications. Check valves with swing-away or flap flaps that pivot on hinges or trunnions to prevent reverse flow are common designs. Swing and flap designs are usually more common in large check valves.

These check valves feature a ball mounted on a sleeve that has a profile that suits the ball. A competent ball check valve manufacturer will help you design the perfect check valve. A duckbill check valve relies on a flexible rubber diaphragm that makes the valve normally closed without the application of positive pressure. In comparison to metal swing or flap valves, rubber duckbill check valves are more reliable and longer-lasting due to their non-rusting, non-seizing, and non-binding characteristics. Rubber check valves are also resistant to mechanical wear, which affects check valves made from other materials.

Choosing The Right Check Valve

The correct choice of check valves depends on many factors. As an example, any check valve should be made from materials that are compatible with the liquid or gas that will be used, such as rubber duckbill check valves. This will include assessing the valve rating, the size,, and type of the line, the installation, the dimensions, the connection type, the maximum leakage rate, the pressure drop, as well as any special requirements. Each application must also be fitted with the correct type of valve.

Degree Of Opening Of A Check

The degree of opening of a check valve depends on the differential pressure, but the fully open gate does not significantly restrict the flow for most types of valves. Yet, the selection of check valves depends on the flow coefficient (Cv) of the valve, rather than actual operating conditions, as they are in other types of valves. In these cases, the valve may only partially open.

When partially opened, valves may experience higher resistance, pressure drop, and valve flutter. As a result of excessive flutter, components are more likely to fail. In the case of check valves, this may allow reverse flow and all the problems that can arise. High Cv values, for example, may be detrimental in check valve applications, since they increase the possibility of partially open valves. Check valve sizing is, therefore, one of those critical factors that we often ignore.

How Often Should You Replace Check Valves?

Plant operators need to ensure proper operation and maintenance of check valves due to the potential negative consequences of faulty parts. Standing water or flooding from corroded or jammed check valves can have health impacts by introducing contaminated water to human bodies. As a result of wear or poor maintenance, check valves can become damaged or leak as a result of water hammer, reverse flow, or leakage.

Maintaining a regular replacement schedule for check valves is important. Engineering products with high quality and experience produce better performances than cheaper ones. Rubber check valves may last as long as 35-50 years, while metal and plastic check valves need to be replaced every 5-7 years. Operators should replace malfunctioning check valves and electrical equipment like a pv combiner box as soon as possible.

Conclusion

A check valve should be sized according to its intended application rather than its line size, in order to ensure full valve operation under typical operating conditions. It is quite common for check valves to malfunction because they are not specified correctly, so the valves themselves are ultimately at fault, rather than their design. We hope this article helps you get a better understanding of check valves and their maintenance.

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