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How to choose right check valve?

August 14, 2019 by denghuang  

Check Valve Selection

Check valve selection and size can be applied in the following ways:

Check Valve Opening Pressure

The equivalent water flow is calculated according to the parameters of flow rate and pressure medium, and then the appropriate caliber and the opening pressure of check valve are selected according to the chart.

Maximum working pressure

The maximum working pressure of the check valve is the maximum pressure that the check valve body and seals can withstand. Charts or tables with pressure information will provide you with different check valve pressure ratings.

Maximum and Minimum Temperatures

Considering the environment and process temperature. Choose check valve in temperature range. Charts or tables with pressure and temperature information will provide you with different check valve pressure ratings at different temperatures.

Check valves are sensitive to flow and rely on pipeline fluids to open and close. Internal disc allows water to flow forward to open the valve. Depending on the design, the disc begins to close the valve as the forward flow decreases or reverses. The re-sealing pressure of the check valve is lower than the rupture pressure. Charts or tables with resealing pressure information will provide you with different check valve pressure ratings.

Compatibility of body and sealing material with medium

The optional materials for check valves are body material, sphere material, elastomer and spring material.

Do not select check valves in the same way as ball valves: according to pipeline size and maximum flow or available Cv requirements. These flow conditions determine the internal performance of the check valve because the disc of the check valve is always in flow. Normally, the pressure drop calculation of check valves is based on the full opening of the check valves, just like ball valves/globe valves.

Connection type

Check valves with different designs can have similar process connections. Check valves are commonly connected by flanges, nominal pipe threads and fittings.

Check Valve Installation

Check Valve Direction

In most cases, spring check valves can be installed at any angle. Lifting check valves can only be installed horizontally without spring closing discs, so that discs can be lowered and closed by gravity.

Installation of cleared check valves

Not all check valves can work in vertical downward flow pipelines, nor can conventional or 90-degree piston check valves work in vertical pipelines without springs, thus pushing the disc back into the flow path. When the valve is fully open, discs in some check valves extend into the pipe. This may interfere with the performance of another valve directly attached to the check valve.

If possible, install the check valve downstream at 3 or 5 diameters away from any connection that may cause vibration.

According to the "flow arrow" shown in the check valve symbols flow direction, so that the valve can perform its function. Check valve flow symbol arrow can be found on the check valve body or label.

Preventing reflux is important because it not only reduces process heating efficiency, but also damages instruments, valves or steam traps. On the contrary, when a downward inclined pipe is not submerged in any position, there is almost no possibility of backflow, so no check valve is needed.

 

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