Hold your horses

[Bruce Seidner]

I picked up a 3/4HP blower designed to inflate those rubber jumpity jump houses the kids play in or keep a 60' sky dancer fabric advertising tube up in the air. The fan blade looks like it came out of a hover craft and it puts out 5200 CFM at it's top speed of 3400RPM. It has two slower speeds of 3100RPM and 2600RPM.

I put up a plywood "wall" to separate my garage work area from a 40x60' crawl space and would like to mount this little beast to the other side and have it pull from the work bench area over which it will preside.

The problem is that this would overwhelm any bag filter that was not ginormous. The calculators I have seen put me at 500 to 1000 sq/ft for good filtration. I want to throttle this little feller back for a filter of more reasonable proportions and cost. I will figure a way to have a choice to exhaust to the outdoors in the meantime and just keep the garage door open making a nice draft for clement weather.

But how to tame this thing? It pulls 7/6/5.5 amps at its 3-speeds. I imagine this requires more than an incandescent light dimmer.

[Stew Hagerty]

Take the specs into your local electrical supply store and they should be able to hook you up with the proper industrial sized rheostat.

[Van Huskey]

What sort of static pressure is it designed to work with?

[Bruce Seidner]

Two helpful questions. Thank you.

I have an electrical supply store just up the street and will ask them.

I could not find the answer to the question about static pressure. These appear to be designed for large volume air floats. There is likely not much resistance to being inflated, but with kids jumping on them or keeping a 60' column of fabric flying in the air and wind there is likely some oomph available but it is not published that I can find. It really moves some air however and it was used and about $35 if I remember correctly.

[Rod Sheridan]

Bruce, I would expect that with the static pressures encountered in filter bags, that you would achieve somewhere around 400 CFM with that blower.

That shouldn't be a problem for any dust collector filter you might find.

Regards, Rod.

P.S.

Make sure you measure the motor current once you install it, if there isn't enough restriction (very low air flow) the motor will be overloaded. You can throttle back the airflow by restricting the blower intake with a sliding baffle.

[Bruce Seidner]

That is interesting Rob, you are suggesting that the problem would be overloading the fan because of the lack of resistance, ie no 60' tall fabric tube advertising the opening of another used car lot. I was concerned that a filter bag could not do its job because of the cfm being blown its way.

The resistance and air loss of a 60' tall nylon tube for which this blower is designed to keep inflated would not in your view overwhelm the filter, forcing it to pass the sub 10micron particles that I wish to capture. It is my understanding that CFM to static pressure is like water gallons flowing softly over something versus a high powered stream capable of etching stone. Is your prediction that it would behave like 400CFM blower the voice of experience and/or do you have some formula in mind. Would you then size the bag for a 400CFM blower? What is the downside of an undersized bag. My guess is that there is loss of dust catching effectiveness and that small particles get forced out.

The fan will be pulling from the shop over the workbench and then to the outside for present. I should have good circulation of air in th shop, while the weather is nice and I can open the garage door.

[Rod Sheridan]

Hi Bruce, those jumping castles have very little air flow requirements, essentially leakage as you need a blower that can be powered by a standard wall receptacle. (This means low horse power).

As the airflow through the fan increases, the power requirements increase if the static pressure stays the same.

If you look at dust extractors, you're in the 3/4 to 1 HP horsepower per 400CFM at normal static pressures for dust collectors.

Since you're not using it with intake piping, you won't have the frictional losses of that, so depending upon your filter material, filter area and airflow, you may get 600CFM, however without a fan curve, it's all a guesstimate.

You will have to measure the motor current, and may have to restrict the airflow to prevent overheating of the motor.

Regards, Rod.