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%.

In the process of full low pressure switching air separation unit​, a bypass valve is usually installed on the pipeline from the air to the switching heat exchanger and from the waste nitrogen to the switching heat exchanger, which plays a very important role in the start-up stage: part of the cooled air can return to the switching heat exchanger through the bypass valve to release the cooling capacity.