The diameter of the butterfly valve is mainly determined by the flow, medium and flow rate. In general, the flow rate of liquid is not more than 5m/s and up to 7-8m/s. In general, the flow rate of water is 2-3m/s, the flow rate of low pressure gas is recommended for 2-10m/s, the flow rate of medium pressure gas is recommended for 10-20m/s; As for the flow rate of steam, the flow rate of low pressure steam is recommended for 20-40m/s, the flow rate of medium pressure steam is 40-60m/s, and the flow rate of high pressure steam is 60-80m/s.

Of course, sometimes, in order to reduce pressure loss, people will choose a larger diameter butterfly valve, so the flow rate will be slower. However, this cannot be done if the valve is operating with a low flow rate.

Liquids flow through a zone of absolute low pressure and undergo rapid evaporation and re-condensation in a very short period of time. This phenomenon is called cavitation effect. Because the gas cannot change state at low pressure, this phenomenon does not occur in the gas stream. When the fluid flows into the high-pressure area, the steam bubbles will suddenly condense, collapse or coalesce, the flow rate can reach 110m/s, the flow pressure can reach 50Mpa, causing impact damage to the pipe wall.

When the valve pressure is less than 1.5Mpa and cavitation occurs, but does not cause serious damage to the material, so no special measures are necessary.