* This is usually the peak load compressor in multiple compressor installations but the calculation can also apply to base load machines. In general, the larger the air receiver, the better and smoother runs the compressor station. ** Maximum permissible cut-in-frequency per hour of the largest switching compressor. Guide figures: Compressors up to 18.5 kW Z=120, up to 75 kW Z=60, over 75 kW Z=30.  *** Critical case: Compressors must switch most frequently when they are run at 50% duty cycle (utilizaton) Utilization factor A = (V2/V1) = 0.5