Compressor Theoretical Displacement

displacement = (pi/4) x bore^2 x stroke x cylinders x RPM, divided by 1728 for CFM. A 2.0 in bore, 1.5 in stroke, 4-cylinder compressor at 1750 RPM sweeps 18.85 in^3/rev, or 19.1 CFM at 100% volumetric efficiency. The actual delivered volume is this times the volumetric efficiency, which falls as the compression ratio rises and the valves and rings leak, so a real machine moves less -- but this is the geometric number to compare two compressors on. Reciprocating positive-displacement only; the rated capacity at the operating condition governs.

displacement_cfm = (pi/4) x bore_in^2 x stroke_in x cylinders x rpm / 1728; displacement_cid_per_rev = (pi/4) x bore^2 x stroke x cylinders.

Reciprocating compressor theoretical (swept-volume) displacement (ASHRAE Refrigeration; positive-displacement compressor geometry), by name; the rated capacity at the operating condition governs.

The swept-volume geometry is first-principles; the bore, stroke, cylinder count, and speed come from the compressor nameplate and spec.

Estimate. AHJ and licensed professional govern.

Field names used by the API: bore_in, stroke_in, cylinders, rpm, displacement_cid_per_rev, displacement_cfm

• 100% volumetric efficiency the theoretical displacement is the ceiling; actual delivered volume = displacement x volumetric efficiencycompressor theory
• Reciprocating only swept-volume geometry applies to piston compressors; scroll/screw/rotary differASHRAE Refrigeration