Blade geometry
| Blade form | Forward, in the direction of rotation |
| Exit blade angle | Above 90° |
| Number of blades | 24 to 48 |
| Air leaving the impeller | At a velocity greater than the blade tip speed. Pressure is developed by the high velocity of air leaving the shallow blades. |
Where it is used
- Low pressure ventilation and air handling
- Packaged air conditioning and air supply units
- Duties where the smallest wheel diameter and lowest speed are wanted
Not suited to dust-laden or erosive airstreams. The shallow, closely spaced blades collect deposit. For such duties see the straight radial and radial tipped types.
Applications selected with this blade
| Application | What it does | Type usually selected |
|---|---|---|
| Ventilation Fan | Moves air through a plant or building for fresh air supply, heat removal and fume dilution where the system is ducted. Low pressure, long hours, so efficiency and noise set the selection. | Backward inclined and forward curved |
| AHU | A packaged unit with fan, filters, cooling or heating coil and mixing box that conditions and delivers supply air. Pre, fine and HEPA filters as the air quality requires. | Backward curved and forward curved |
| HVAC | Supply, return and exhaust fans for heating, ventilation and air conditioning of plant and office space. Low pressure, so efficiency and noise govern. | Axial, backward inclined and forward curved |
Industries
SugarPaperTobaccoTeaFood ProcessingAutomobileSurface CoatingDyeing IndustriesTyreShipbuildingNuclearChemical & Pharma
Drive and construction
Offered direct mounted on the motor shaft, direct coupled, or belt driven. Material of construction follows the medium and temperature: mild steel, stainless steel, PP-FRP lined, MS FRP lined or MS rubber lined.
Testing and balancing
Performance tested as per IS 4894, BS 848 Part I, or as per customer standards. Rotors are statically and dynamically balanced to grade G 6.3 or G 2.5 as per ISO 21940-11.
Information needed to select or quote
- Duty point. Volume flow and static pressure at the fan inlet, with the gas density and temperature or the conditions to derive it.
- Operating conditions. Site altitude, normal operating temperature and continuous or intermittent duty.
- Gas stream. Dust loading and particle size, corrosive species, moisture, upset temperature and any tendency of the material to deposit on the impeller.
- Mechanical. Rotation viewed from the drive end, discharge orientation and motor power.