The gas concentration in the machine room seriously exceeds the standard. The main reasons are as follows: ① due to the small number of equivalent teeth and relatively few times of throttling expansion, the leakage is serious; ② When the unit passes the critical speed or abnormal vibration occurs, the amplitude is large, and there will be contact between the teeth on the rotor and the sealing sleeve. Due to the thin sealing teeth caused by pulling apart, when friction occurs, it will be quickly worn and the sealing gap will increase, resulting in gas leakage.