Backward Inclined Blower wheels are constructed of steel using flat single thickness blades, continuously welded to the rim and the backplate. Note that the use of a conical spun shroud (rim) makes BC/AF Blowers less susceptible to the performance losses associated with poor inlet conditions. All BC and AF Blower wheels are statically and dynamically balanced to grade G6.3 per ANSI S2.19 for smooth operation prior to being assembled in the Blower, followed by final balance of the entire rotating assembly.
Bearings are a heavy-duty, grease lubricated, anti-friction ball or roller, self-aligning, pillow block type, selected for minimum average bearing life (AFBMA L-50) in excess of 200,000 hours at the maximum fan RPM.
Shafts are AISI Grade 1040, 1045 hot -rolled steel or Stainless Steel, accurately turned, ground, polished, and ring gauged for accuracy. Shafts are generously sized for first critical speed of at least 1.43 times the maximum speed for the class.
Variable inlet vanes cause the entering air to pre-spin in the direction of wheel rotation, resulting in reduction in volume, static pressure and brake horsepower and thus providing an infinite number of fan curves approximately parallel to the original fan curve. Variable inlet vanes cost about 50% to 80% more than outlet dampers but offer significant savings in energy. Because of their simplicity, inlet vanes can be more reliable when compared to variable frequency drives.
There are two types of variable inlet vanes: nested (internal type) and bolted on (external type).
The closing of an outlet damper adds to the resistance that the Blower is working against. This moves the operating point to the left of the initial rating point. The savings in horsepower depends on the relative position on the fan Cone and is usually much less than offered by other methods. Outlet dampers are typically the least expensive option and should be considered when infrequent operation at lesser capacity is desired or when handling hot, humid or particulate laden air.
There are two types of outlet dampers: parallel blade and opposed blade. Parallel blade dampers are recommended for systems where air volume is modulated between full-open to about 75% of open. Opposed blade dampers cost about 10% more and are recommended for systems where volume is modulated over the entire range. Opposed blades reduce air volume in a closer relationship to the control arm movement.
Belt guard protects personnel from the moving drive parts. Both standard and totally enclosed type guards are available. Shaft Guards Solid or expanded metal guards cover shaft and bearings and or drive couplings are provided with access holes for bearing lubrication. Modified for ventilation on units with shaft cooler.