Capacity rating terminology for compressors: On a nameplate, a “3 m³/min compressor” most commonly indicates that the machine handles which volumetric flow basis?

Difficulty: Easy

Correct Answer: compresses 3 m³/min of free air (at local atmospheric conditions)

Explanation:


Introduction / Context:
Compressor capacities are quoted in different “bases” such as free air, standard air, or compressed (actual) conditions. Knowing what a “3 m³/min compressor” means prevents sizing mistakes and ensures apples-to-apples comparison between vendors.


Given Data / Assumptions:

  • Nameplate says 3 m³/min, no further qualifiers.
  • Industry convention: unless explicitly marked as “standard” or given discharge state, volumetric flow refers to free air basis.
  • Free air means volume referenced to the site’s atmospheric pressure and temperature.


Concept / Approach:

Three common bases exist. Free Air Delivery (FAD) expresses the delivered mass flow as an equivalent volume at local ambient conditions. Standard air uses a fixed reference (e.g., 1.013 bar and 15–20°C). Compressed (actual) volume is the discharge volume at delivery pressure/temperature. Unqualified ratings in general practice imply FAD, not standard or compressed volume.


Step-by-Step Solution:

Identify unspecified rating → adopt industry default (FAD).Relate mass flow to FAD volume at site ambient.Conclude the nameplate indicates 3 m³/min of free air.Select the option that explicitly states “free air”.


Verification / Alternative check:

Vendor datasheets typically label exceptions explicitly (SCFM/Nm³/h or “at discharge state”). Absence of such labels supports interpreting the figure as FAD.


Why Other Options Are Wrong:

Standard air requires a declared standard; compressed-state volume depends on discharge conditions; stating “at delivery pressure and temperature” would need exact values, which are not given.


Common Pitfalls:

Confusing FAD with SCFM/Nm³/h; comparing different bases without conversion; overlooking ambient altitude/temperature impacts on FAD.


Final Answer:

compresses 3 m³/min of free air (at local atmospheric conditions)

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