First, check that there isn't a very high air demand, or air leak somewhere. If the capacity of the air compressor is really too low, check the following: Check differential pressure over oil separator. Replace separator when necessary. Check and replace compressed air filters (if installed).
[pdf] For water-lubricated twin-screw compressors, the estimation of leakage flow remains one of the most important problems related to screw compressor design, performance prediction and improvement. In this.
[pdf] Check for correct oil level at the ll plug location on the compressor. The oil level is full when oil is at the bottom of the threads in the ll plug hole. Check for oil purging from the air dryer. Refer to the image below as an example.
[pdf] 
