A volume of 6 to 10 times the litres per second is not in keeping with the Best Practice dispensed here in North America. In our terms this would result in only 600 gallons of storage for a 500 cfm 100 hp (75 kW) compressor. Best Practice would be 2,500 to 5,000 gallons (9,500 to 19,000 litres) I would suggest the better size would be 6 to 10 times the litres per minute.

Of course it depends on if the compressor is air cooled or liquid cooled (the 30% mentioned doesn’t include the cooling fan). but there are many compressor that get down in the 25 to 35% of power level if they are properly maintained.

Be sure you are not just taking the motor amp draw and assuming this is directly related to power. Measure with an actual power meter. Compressor motors have a lower power factor when they are unloaded, running on average about 0.6 compared to about 0.85 when loaded. This results in higher amps but lower power if you multiply it out using the power formula. Watts = amps x volts x power factor. The change in power factor loaded versus unloaded, resulting in amps dropping to only 50%, gives the impression that the power only drops to 50 or 60 percent,when it actually drops more (50% x 0.6 = 30%).

This being said there are compressors out there will faulty blow down circuits or some older units with no sump blow down at all. I found one last week where the power dropped to only 72%, but this is not normal.