Small blower/vac with fanblade?

[Number21]

I want to build a gas powered blower/vacuum with a 6.5hp engine I have. I also have a big old 7 blade fan from a 70s ford big block which I could easily attach to the engine.

If I built a plywood/sheetmetal enclosure for the fan, with very close tolerences and a 6" suction hose/output port, would it actually have any sucking or blowing power? Or would it be better to design a blade from scratch?

 

[Treemonkey1000]

I think that I would just look for an old backpack blower from Craigslist or Ebay. If you have the skills and desire to try what you were thinking something that is already built up could be a thing you would pick up for cheap. It might need some work if you found one cheap enough. I use a backpack blower around my house and love it. Dirt and gravel as well as tree needles and leaves. It works good on cleaning out the gutters as well.

 

[RonMar]

I don't think it is going to work very well. That fan just wasn't meant to build any real pressure/vacume. Most fans are high volume low pressure devices, and as soon as you restrict their flow too much, they stall and cavitate and the air just flows around and bypasses the blade.

Vacumes use centrifugal blowers. These are capable of developing high pressure/vacume. You could probably make one out of a round plate and some carefully cut sections of large round pipe for the blades that would be welded to the plate. A little more calculation needs to be brought to bear as a 3600 RPM spinning plate can generate some pretty serious forces if something fails...

 

[MJPetersen]

A little more calculation needs to be brought to bear as a 3600 RPM spinning plate can generate some pretty serious forces if something fails...

Not to mention the critical balance necessary at 3600 rpm. The vibration of out of balance will take out the bearings in a small engine.

Mike

 

[Number21]

I use a backpack blower around my house and love it. Dirt and gravel as well as tree needles and leaves. It works good on cleaning out the gutters as well.

What brand is this? Would it literally pick up a pile of loose dirt/gravel?

I checked out craigslist already but didn't see anything but worn out cheap brand crap. I'm looking for lots of power.

 

[Treemonkey1000]

This is a Homelite Model UTO8111A. I don't remember the CC's of the motor. They make more powerful ones. Echo and Stihl probably. It will blow gravel. The tip of the hose is flattened out some to help aim the airflow better. It isn't the top of the line but it works well for what I need. The exhaust from the engine is even purged into the airflow.
Jim

 

[RonMar]

The backpack blower/vacs will vacume dirt and gravel, but it is not advisable as whatever is vacumed passes thru the blower impeller(usually made of plastic) and will eventually damage it. The Stihl handheld blower/vac I have, has a little chopper blade bolted on in the center of the impeller to shred leaves and grass to reduce the volume that is added to the bag...

 

[Treemonkey1000]

Good point Ron. This backpack blower just blows out air and doesn't pick up stuff. I will blow it into a pile if I need then shovel it.
Jim

 

[Number21]

Hmmm...I'm still wanting to build a vacuum with my 6.5hp engine...but I DON'T want the trash to be sucked through the blades...kind of like a shop vac.

What if I build my own 4 blade impellar using a 2x2 backbone and some 1/4" plywood blades. The inside corner of the blades could be cut on a 45* angle, much like some electric blowers I've seen? Obviously it would have to be balanaced, but I don't trust my welding at 3600RPM...

 

[Treemonkey1000]

You could just strap a shop vac onto your back. Drive it with a little 2 stroke motor...

 

[Number21]

You could just strap a shop vac onto your back. Drive it with a little 2 stroke motor...

Problem is I don't want a little 2 stroke motor. I want my 6.5hp monster.

 

[joes_427_vette]

The ford fan unit won't be very useful as it is intended to draw small volumes of air through the radiator cores an inch away. If you look at lawn vacuums they have a 8-10 inch diameter piece of steel with 3-4 inch blades. The flat blade area is what is going to move massive amounts of air ( and what ever is fed into the system > ). Two cycle engines benefit from the small blades and short fins with the thousands of rpm they produce blowing but little vacuum capabilities.

 

[RonMar]

Fans are HIGH volume LOW pressure... Actually those little high speed two stroke impellar/blowers generate quite a lot of vacume. My little 30CC monster lifts leaves and grass up a 4' diameter pipe at pretty high velocity. But you are correct, that it gets this by high RPM. The same thing can be achieved with a larger diameter impellar at lower RPM though.

As for a blower for a 6.5Hp 3600 RPM engine, I think I would trust steel and welds before I would trust something assembled out of plywood. You could fabricate something similar to a shopvac/turbocharger impellar,



which would need to be installed in a tight fitting caseing. This one shown would spin counterclockwise as seen with the air being slung outward from the center. It would of course need a center boss with keyway to match your engine shaft. You would need to plumb the center of the blower housing(low pressure point) to the side of a sealed box near the top. You could then feed the box from the other side just like a large shop vac.