Machines that move gases at high flow with a small pressure rise (ratio < ~1.1) — the air behaves as incompressible and the design is dominated by blade aerodynamics, not compression thermodynamics.
Usual types
(handbooks per type in Phase 1)
- Axial — flow parallel to the shaft: propeller (wall), tubeaxial and vaneaxial (with stator);
- Centrifugal — backward-curved blades (efficient, non-overloading), forward-curved blades (compact, overload-sensitive) and radial blades (particulate-laden gas);
- Mixed flow — intermediate between the two.
Exhausters are the same principle with an extraction duty: removing stale air, smoke and particulates (the arrangement inverts — the machine draws from the controlled space).
In ISO 14224:2016 the fan has no dedicated class — it appears as a subunit of other equipment (e.g. the fan of an API 661 air cooler). Testing and selection practice follows AMCA/ASME PTC 11. Reliability: unbalance and blade build-up, bearings and belt drives dominate the failure history.