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CAGI Standards // ISO 1217 Annex C

CFM to FAD & Pump-Up Test Calculator

Convert empirical receiver tank pump-up duration into true Free Air Delivery (FAD CFM) according to ISO 1217 Annex C standards, isolating thermal air-heating losses and internal rotor clearance degradation.

Benchmark Compressor Package

Pump-Up Test Empirical Readings

200 Gallons (26.7 ft³)

Total storage volume downstream of compressor discharge check valve (exclude downstream piping if isolated).

105 seconds (1.75 min)

Stopwatch duration required to pressurize from P1 to P2.

psig
Initial tank gauge reading (0 for empty tank)
psig
Final cutoff pressure gauge reading
°F
°F
Delivered Capacity (FAD)
125.9FAD CFM
(3.56 m³/min / 59.4 L/s)
Volumetric Health vs Rating96.8%
Nominal Rating: 130 CFM (30 HP Package)
Optimal Performance

Compressors experiencing >15% volumetric decay require inspection of air intake throttling valves, separator element differential pressure, and screw rotor blowby.

Specific Energy Profile

Estimated Input Power:24.3 kW
Specific Power (kW / 100 CFM):19.3 kW / 100 CFM
CAGI Benchmark Target:16.0 - 20.0 kW / 100 CFM
Thermal Expansion Loss Factor:3.1%
CAGI Testing Protocols

The Physics of Free Air Delivery (FAD) & Pump-Up Testing

1. Why Nominal CFM Differs From FAD

Compressor manufacturers frequently advertise displacement CFM (the theoretical volume swept by pistons or rotors). Free Air Delivery (FAD), defined by ISO 1217 Annex C, measures the actual volume of ambient air ingested and discharged under site barometric conditions:

FAD = [V_tank × (P2 - P1)] / [P_atm × t] × [T_inlet / T_tank]

Without the absolute temperature correction factor (T_inlet / T_tank in Rankine or Kelvin), thermal expansion inside the hot receiver tank falsely inflates calculated flow rates by 4% to 9%.

2. Identifying Air End Clearance Degradation

As rotary screw compressors accumulate tens of thousands of operating hours, Teflon/Viton rotor coatings erode and bearing tolerances relax:

  • Internal Backflow: Hot compressed air slips back past rotor meshing clearances into the suction housing, degrading volumetric output without lowering motor current draw.
  • Specific Power Surge: A decaying air end consumes the same nominal kilowatt-hours while delivering substantially lower CFM, sharply elevating utility operating costs.
  • Preventative Threshold: If pump-up testing reveals capacity falling below 85% of factory CAGI datasheet ratings, overhaul or rotary air end exchange is recommended.