Air compressors — what does “free air delivery (FAD)” actually mean? In compressor testing and selection, the term free air delivery refers to which of the following definitions?

Introduction / Context:
Manufacturers specify compressor capacity using standardized terms so that users can compare across different machines. “Free air delivery (FAD)” is a widely used capacity metric that normalizes the delivered air volume to standard conditions (often 1.013 bar and 15 °C or as otherwise stated).

Given Data / Assumptions:

• Steady compressor operation.
• Standard reference conditions are clearly defined by the test code (e.g., ISO or CAGI).
• We are seeking the definition, not a numerical calculation.

Concept / Approach:
Because gas volume varies with pressure and temperature, a direct volumetric reading at discharge cannot be compared between machines. FAD converts the delivered mass flow to an equivalent volume at standard temperature and pressure so capacities can be compared on an equal basis.

Step-by-Step Solution:
Measure delivered mass flow or discharge volume with known P, T.Convert to equivalent volume at standard P_std and T_std using ideal-gas relations.Report this normalized volume as the compressor’s FAD.

Verification / Alternative check:
Handbooks and standards define FAD as the volume of air delivered when reduced to standard conditions, confirming option (a).

Why Other Options Are Wrong:
(b) lacks normalization; (c) is intake swept volume, not delivered after losses; (d) ignores clearance/slip; (e) is a mass-based expression, not the FAD definition.

Common Pitfalls:
Not checking which “standard conditions” are used—values vary by region and standard, so always cite the reference.

Final Answer:
The actual volume of air delivered, referred back to standard (normal) temperature and pressure conditions