05-14-2015, 07:57 AM
There are several variations on "squirrel cage" blowers. If yours is out of a household type of furnace or air conditioner, it is likely a "forward curved" wheel. They are easy to identify - the air foils are short compared to their length, and have a obvious curve formed into them. The curve is in the "forward" direction of rotation.
These wheels operate with low noise and are compact, but are designed to operate against a minimum range of discharge pressure. If you don't have enough pressure across the blower, the blower will overload the motor.
It seems counter-intuitive, but a centrifugal blower requires the least power when the air flow is totally blocked. The power requirement goes up as the restriction is decreased and reaches a maximum at "unrestricted flow."
Try an experiment. Use a piece of cardboard to restrict the blower flow. You can do it either on the discharge or on the inlet, but the inlet is usually easier. Put your amp meter on the motor and measure amps at several points from no restriction to fully closed. You will find the amps fall off considerably as the blower is restricted.
Your ventilation application might require some restriction to limit the motor amps to a reasonable level while still giving the desired air flow.
Terry S.
These wheels operate with low noise and are compact, but are designed to operate against a minimum range of discharge pressure. If you don't have enough pressure across the blower, the blower will overload the motor.
It seems counter-intuitive, but a centrifugal blower requires the least power when the air flow is totally blocked. The power requirement goes up as the restriction is decreased and reaches a maximum at "unrestricted flow."
Try an experiment. Use a piece of cardboard to restrict the blower flow. You can do it either on the discharge or on the inlet, but the inlet is usually easier. Put your amp meter on the motor and measure amps at several points from no restriction to fully closed. You will find the amps fall off considerably as the blower is restricted.
Your ventilation application might require some restriction to limit the motor amps to a reasonable level while still giving the desired air flow.
Terry S.