How to select the pneumatic control valve from the functional consideration

1. Adjustment function

① It is required that the regulating valve operates stably; ② the small opening has good regulating performance; ③ the required flow characteristics are selected; ④ the adjustable ratio is met; ⑤ the resistance is small and the flow ratio is large (the ratio of the rated flow parameters of the regulating valve to the nominal diameter); ⑥ the regulating speed.

2. Leakage and cut-off pressure difference

These are two inseparable and interrelated factors. The leakage shall meet the process requirements, and there are reliable protection measures for the sealing surface; the cut-off pressure difference (the pressure difference when the valve is closed) must be proposed (unfortunately, there is no such parameter in the calculation specification of many design institutes' regulating valves), so that the selected regulating valve has enough output force to overcome it, otherwise, the actuator will be selected large or small.

3, anti blocking

Even if the medium is clean, there is blocking problem, which is that the unclean things in the pipeline are blocked by the medium brought into the regulating valve, which is a common fault, so the anti blocking performance of the regulating valve should be considered. Generally, the anti blocking performance of angle stroke type control valve is much better than that of straight stroke type, so the use of angle stroke type control valve will be more and more in the future.

4, corrosion resistance

It includes erosion, cavitation and corrosion resistance. It mainly involves the selection of materials and the service life of the control valve, as well as the economy. The essence of this problem is that the selected valve has good corrosion resistance and reasonable price. If you can choose all Teflon valve, you should not choose all corrosion-resistant alloy control valve; if you can choose angle high-pressure control valve with good anti cavitation effect and simple structure (meeting the service life of about two years), you should not choose other high-pressure control valves with complex structure and expensive price.

5. Withstand voltage and temperature

This involves the selection of the nominal pressure and working temperature of the regulating valve. In terms of pressure resistance, if only the pressure is high, it is not difficult, mainly because the pressure difference will produce cavitation; in terms of temperature resistance, it is very easy to solve the problem below 450 ℃, and it is not difficult to solve the problem between 450 ℃ and 600 ℃, but when the temperature is above 600 ℃, the contradiction will be prominent; when the temperature is 80 ℃, it is generally not advisable to select soft sealing material for the cut-off type regulating valve, and hard sealing cut-off should be considered.

6. Weight and appearance

This problem is very intuitive, it must be a good appearance, light weight control valve by the use of manufacturers welcome. Here, we need to change a prejudice that the regulating valve is a "big brother, thick". It's nothing to be a little heavy or poor in appearance. Now we attach great importance to it, so we put forward that the regulating valve should have the characteristics of miniaturization, lightness and instrumentation.