No match between flowmeter measurement and air piston compressor expected capacity

[compguy22]

Hello,

I have log data of flow meter measurements on the discharge line of a 40 bar piston type air compressor (400 kW).
Measurements were taken downstream dryer, at the air receiver.
The problem is that the capacity measured is 33% below the compressor nameplate capacity which as FAD at ISO conditions is approx. 1350 cfm. The site is 900 m altitude and humidity is 60%.

I am not aware of leakages nor of blow off of air and the condensate coming out of dryer is expected to be not significant.

What could explain the flow difference between measured and expected:

- FAD capacity correction to altitude
- Instrument calibration issues
- Any compressor complicated controls
- Recirculation line or blow off on the piston compressor (I am not aware of)
- Combination?

Can you please provide some guidance?

Thank you

 

[compguy22]

can the air receiver explains such difference, means as the receiver would lead to stable flow downstream but lower rate versus a fluctuating flow upstream but at higher flow rate.

 

[georgeverghese]

For both TSA and PSA type air driers, the regeneration - purge air flow (to blowoff) for regeneration of the spent unit is a significant proportion of feed air - you may find the recommended regeneration air rate in the catalogue for the drier.