Selection of check valves
Most check valves are selected based on the closing speed required for the minimum impact pressure or impact-free closing, as well as a qualitative analysis of the closing speed characteristics. This selection method may not be precise, but based on experience, it is applicable to most usage scenarios.
Check valves for incompressible fluids
The check valve used for incompressible fluids is mainly selected based on its performance that it will not cause an unacceptable high impact pressure due to sudden closure caused by the backflow of the medium when closing. The first step in choosing this type of check valve is to assess the required closing speed. The second step is to select the type of check valve that may meet the required closing speed.
(2) Check valves for compressible fluids
For compressible fluids, the selected check valve should minimize the impact of the valve disc. However, the selection can be made based on a similar method for choosing check valves for incompressible fluids as mentioned above. However, for conveying pipelines with very large diameters, the impact force of the compressible medium may also become quite considerable.
If the medium flow fluctuates greatly, a deceleration device can be used for the check valve of compressible fluids. This device functions throughout the entire displacement process of the closing member to prevent rapid and continuous hammering at its end.
If the medium flow continuously and rapidly stops and starts, such as at the outlet of a compressor, a lift check valve should be used. This check valve features a lightweight spring disc with a relatively low lift degree.
(3) Determination of the size of the check valve
The check valve should have its diameter size determined so that the normal fluid can keep the closing member stably open. To achieve the fastest closing time, the check valve should start closing as soon as possible after the speed of the co-flowing medium begins to slow down. In order to determine the diameter size of the valve in this situation, the valve manufacturer must provide appropriate reference books for determining the size. These data include: providing pressure drops for different fluids; The fully open position of the valve is marked on the fluid coordinate curve. At the same time, the through-hole area of a specific valve diameter size should also be displayed. In this way, the size of the valve diameter when the valve is fully open at a given flow rate can be found.
In conclusion, as various types of valves have their own advantages and disadvantages, when making a selection, valve purchasers should choose valves reasonably and correctly based on different uses.

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