Hi,

For the machines my company builds, I use an industrial fan to push air through an electric duct heater on its way to a dryer, and I use a similar fan to remove the heated air from the dryer (along with some solvent that is removed from the product I am drying).

When I buy these fans (which are typically rated to deliver somewhere around 1500 CFM @ SP 2.5 in wg @ 1800 rpm), the fans come with an arrow that indicates the correct direction of rotation. I don't have one powered at the moment to test myself, but I was wondering if anyone here could tell me for a typical fan, what would happen if we ran the fan in the opposite direction?

Would I the resulting air flow direction be such that air would flow into the blower outlet and out of the blower inlet?

Or, would the air flow direction be such that air would still flow into the blower inlet and out of the blower outlet, only with less than the rated cfm?

The reason I ask is because we have a customer that actually is running one of our (supply) blowers in the wrong direction, and they are unwilling to change it because they have conducted trials and a lot of FDA product qualification paperwork that they are afraid will have to be re-done if the switch the blower direction. If air is moving opposite of our intended direction, I can't comprehend how our furnace systems would even work. If air is moving in our intended direction (but with less than rated air flow), I can at least make some sense of it.

Thanks in advance,
Paul

 

It depends on the style of fan. If squirrel cage, it will not work to change the rotation. If propeller style, it will move air but not as much. How much less will depend on the design.

 

The blower will still push air in the same direction but with much less volume depending on the blade curvature.

Regards
cww

 

> It depends on the style of fan. If squirrel cage, it will not work to change
> the rotation. If propeller style, it will move air but not as much. How much
> less will depend on the design.

I think it's the other way around. A propeller type fan WILL change the direction of air flow, a squirrel cage blower will not, but the flow will be lower and efficiency is lower if you rotate it in the direction it was not designed for. Squirrel cage blowers can have forward swept or backward swept blades or straight (axial) blades, but the airflow <i>direction</i> through the blower is the same regardless. So if you have a backward swept design and run it in reverse, the air flow looks the same, but with less flow and/or static pressure.

 

> The blower will still push air in the same direction but
> with much less volume depending on the blade curvature.

I think you are wrong this time Curt, a propeller when driven in the opposite direction will make the ship go in reverse.
An axial fan or centrifugal pump will go the same way.