Home made shop air cleaner

[jscott2]

I'm planning to us a furnace blower with a 1/2 hp, multi-speed motor running on it's lowest speed, to make a ceiling mounted air cleaner for my shop - it's about 22'x12'x7'.  (I know, it could be a head-knocker.)

When the blower is run on the bench, in free air, the motor draws twice it's design current - not good.  It also moves so much air that I'm afraid it will blow off what little hair I still have on my head.      I know that the air filters will reduce the air flow and current draw but I'm not sure if it would be enough.

I could start building a box with filters over the inlet but I thought I'd check with the forum before I start.  Have any of you used a furnace blower for a shop air cleaner and did it work out well?  Was the air flow too high or did the filters cut the air flow significantly?  Any tricks I should know about?

I'm not sure just what questions to ask but any suggestions would be appreciated.

Thanks,
Jim

[Gabby]

Jim have you thought about setting it up so that it would pull the dust away from you and possibly vent outside. Much like a painters booth. Adding resistance by adding filters should cause a greater current draw, I'd check and see if it needs lube or has some other problem before spending a lot of time building a system for it. See if you have a motor repair service locally where they could check it out if you don't have the expertise.
I hope this helps,
Gabby

[tvman44]

Cover up part of the discharge this will reduce the current draw.  What I do is take a piece of plywood and start covering the discharge till the current is the same as the rated draw then make a permanent blockage to cover that amount.  We have done this many times and it works well.  The reason  for the excessive current draw is no back pressure, when it was used in a system the duct work provided some back pressure.

[joey65746]

sounds like you have a great fan to set up you a sanding and painting table like said above you could set it up to pull the dust from where you are working and blow it out side like a paint booth  or you could make you a down draft table for sanding  the ideas are endless  and how you was thanking wood work great to and wood cool your shop off in the summer    i have been looking at maken me a down draft table to get rid of the sanding dust and for spraying finsh wood be great    if you are looking to make a cheap air filter i do like others i use a box fan with filters on the back side and i clean them about every day they catch so much dust  ideas are endless  hope this helps

[jscott2]

Gabby, my shop is in the basement (Montreal, Quebec) so venting outside will waste either heat or air conditioning.  The fan bearings are good, it takes quite a while to stop spinning.  

Tvman, I've tried partly blocking the inlet, and partly blocking the outlet, and partly blocking both.  That reduces the current draw but when I get it where I think the air flow is good, the whole fan starts vibrating.  It's a direct drive type so that would be especially hard on the motor bearings.  You are correct that the house ducts provide resistance to both slow down the air flow and reduce the current draw.

Joey, I thought about a sanding table but don't have room in the shop.  My table saw and drill pres table are used a lot for assembly, painting, etc.  I was also thinking of better filtering than is possible with a box fan.  I working on a paint both that will discharge outside through a window.

I have a dust collector with one hose that can be connected to each machine as needed, including above and below the table of the scroll saw.  SWMBO doesn't like dust getting into the house thus the air cleaner.

I guess I'll end up making a box for the fan, putting in some filters, and perhaps partly blocking the outlet until I get what I want.

Thanks for all your replies.  From the beginning of the project I suspected it would end up being a trial and error build but thought that someone with more experience than I might have a definite solution.

Jim

[BilltheDiver]

Jim,  You might consider making this same post over on www.lumberjocks.com.  A lot of the guys over there are really proficient at dust collection and many have made different types of air filters and so forth.

[Gabby]

LOL
So I was wron uh, er, uhhmm, mistaken about adding resistance. Isn't the first time probably won't be the last. 
Gabby

[jscott2]

Gabby, you're right about adding resistance, i.e., filters, to the system.  I found blocking the inlets and outlets did reduce the current draw to reasonable levels but then the whole fan body started to shake.  Perhaps if I actually used filters instead of two pieces of cardboard with openings cut in them, it wouldn't shake as much. 

Bill, good idea about lumberjocks.  I haven't posted yet but have read all the air cleaner posts.  Unfortunately I didn't see anything to answer my questions.

Perhaps I am over-thinking the problem.  (I've been known to do that.)  I'll have to build a box and see what happens, and make sure I can add extra layers of filters, and/or partly block the outlet, if needed.

Thanks,
Jim

[jscott2]

Did some more work the the project and found some interesting results that might help others in their quest for a clean(er) shop. 

All the furnace fans I have seen have forward curved blades and I read that backward curved blades push less air.  I turned the squirrel cage of the direct drive fan so it was like a backwards curved cage.  It did reduce the flow somewhat but the fan vibrated too much at all speeds.  So much for that idea.

I also have a belt drive blower that happens to be the same rating as the direct drive.  Turning the cage around so it is backwards reduced the flow and the fan ran as smooth as silk.  That was a pleasant surprise after my experience with the direct drive.  There is also more flexibility to adjust the air flow by changing pulley sizes.

While I was doing the experiments with the blowers, I found a 10" diameter, 1500 rpm propeller type fan and installed that in the filter box I had made for the direct drive fan.  It is working very well so I think I will stick with that one for a while.

If you are thinking about building an air cleaner around a furnace fan, you might be happier making a larger box to enclose a belt drive unit, especially if you want to reduce the flow.

Happy April Fool's Day,
Jim