What is the air displacement of an air compressor?
Displacement is a key technical parameter for evaluating an air compressor’s air-supply capacity, typically defined as the volume of gas discharged by the compressor per unit time. It directly influences system‑air‑demand matching and energy‑efficiency performance.
FAD: The internationally recognized standard for actual displacement volume
FAD (Free Air Delivery), or “free air flow,” refers to the volumetric flow rate of air at the inlet under standard conditions (typically 101. 325 kPa, 20℃ The actual volumetric flow rate measured under standard conditions (e.g., 0% relative humidity) is commonly expressed in m³/min or L/s. FAD reflects the truly usable air volume and serves as a critical basis for equipment selection and acceptance testing.
The difference between actual displacement and volumetric flow rate
- Volumetric flow rate: Theoretical value, calculated based on the cylinder’s geometric dimensions and rotational speed, without accounting for losses such as leakage, intake resistance, or temperature variations;
- Actual displacement volume: The measured value, influenced by intake conditions, compression efficiency, pipeline pressure losses, and cooling performance, is typically lower than the volumetric flow rate.
- FAD falls under the category of actual displacement, but it strictly specifies test conditions, ensuring comparability.
Simplified estimation method (for reference only)
If field measurements are unavailable, a rough estimate can be made using an empirical coefficient: FAD ≈ volumetric flow rate × 0.6–0.85. The choice of coefficient depends on the equipment type, pressure class, and operating‑maintenance condition—higher values apply to high‑efficiency screw compressors, while lower values are appropriate for older reciprocating compressors. Precise calculations must be performed via on‑site testing in accordance with ISO 1217.