Generally, there are three types of expanders, namely, low-pressure expander, medium pressure expander and liquid expander. For a certain type of gas expander, the greater the volume flow of working medium, the higher the efficiency. Generally, the efficiency of the low-pressure expander with a flow of more than 8000nm is 85 ∽ 88%, and the efficiency of the expander with a flow of less than 3000 ∽ 8000nm will be as low as 70 ∽ 80%.