To select valves, first of all, we need to master the medium performance, flow characteristics, and temperature, pressure, flow rate, flow and other performance. Then, combined with the process, operation, safety and other factors, we need to select the corresponding types, structural forms, models and specifications of valves.

1 select valves according to flow characteristics

The shape of valve opening and closing parts and valve flow passage makes the valve have certain flow characteristics. This must be taken into account when selecting valves.

(1) valve for cutting off and connecting medium

Generally, the valve with small flow resistance and through flow channel is selected. This kind of valve has gate valve, stop valve, plunger valve. Downward closed valve, due to zigzag flow path, flow resistance higher than other valves, so less choice. However, in the case of high flow resistance, closed valve can also be selected.

(2) valve for flow control

Usually choose the valve which is easy to adjust the flow. For example, regulating valve, throttle valve and plunger valve, because its seat size is in direct proportion to the stroke of the starter. Rotary (such as plug valve, ball valve, butterfly valve) and flex (pinch valve, diaphragm valve) valves can also be used for throttling control, but they are usually only applicable within the limited valve diameter range. In most cases, people usually change the shape of the disc of the stop valve for throttling. It should be pointed out that it is unreasonable to change the opening height of gate valve or stop valve to achieve throttling. Because the medium in the pipeline is in throttling state, the flow rate is very high, the sealing surface is easy to be washed and worn, and the sealing function is lost. Similarly, it is unreasonable to use the throttle valve as the cutting device.

(3) valve for reversing and diverting

According to the need of reversing and shunting, the valve can have two or more channels, which is suitable for selection of plug valve and ball valve. Most of the valves used for reversing and diverting are of this type. In some cases, other types of valves, with two or more only properly connected to each other, can also be used as the commutation and shunting of media.

(4) valve for medium with suspended particles

If the medium has suspended particles, it is most suitable to use its opening and closing parts to slide the valve with wiping function along the sealing surface, such as flat gate valve.