PTO leaf blower

[SkunkWerX]

Be advised that a squirrel-caged fan will work well up to a certain speed, but if you over-drive it, and spin it too fast, it will go into a stalled-air condition, where it is spinning much faster , but, not able to push the same volume as it could at its intended speed. It has something to do with the intake side not being able to suck enough air fast enough so it creates a sort of vacuum in the cage.....don't quote me on the details, but hopefully you get the picture.

My understanding of this is not entirely clear, but, as best as I can remember, a squirrel caged fan needs a semi-restricted inlet to function efficiently, yet, it is the same thing that causes problems at the point you over-spin it.

Bottom line, if you think you can increase your RPMs by varying pulley sizes, and thus Super-charge your air output, be aware there is a drop-off point where you will lose a lot of air flow due to the aforementioned condition.

Ask me how I found this out?
Hint: when i saw the picture assocaited with the first post it brought back those memories....

 

[Grrrr]

Ask me how I found this out?

OK, I'll ask then

 

[oliver28472]

My brother has a big one made from a silo blower. It will get the job done. Too big for my little tractors though. He uses it on a 485 Case-IH.

 

[SkunkWerX]

OK, I'll ask then

I got a very large pulley, and a very small pulley, figuring i would spin a squirrel cage fan 4x as fast as it was rated.

What a surpirse when the output was equal to a desk fan on low speed.

 

[midcarolina]

My understanding of this is not entirely clear, but, as best as I can remember, a squirrel caged fan needs a semi-restricted inlet to function efficiently, yet, it is the same thing that causes problems at the point you over-spin it.

That is correct, The curve of the blades are engineered to work efficiently at a certain rpm range at a certain static pressure range.

For those of you who have one in your shop take a piece of cardboard or sheetmetal and partially block the intake you will hear the rpm's go up considerably.

On an application like a leaf blower I would make an adjustable deflector on the discharge this would accomplish the same thing, plus you can direct the air in a downward pattern..........

 

[Donman]

With 2 pto speeds plus infinately variable throttle positions and six gears forward, I should be able to find the right combination to work this thing the best. I'll let you all know what works best when I get to use it next. Believe it or not we still have a lot of leaves on the trees up here in Michigan.

 

[jimmysisson]

For those of you who have one in your shop take a piece of cardboard or sheetmetal and partially block the intake you will hear the rpm's go up considerably.

A fan is a pump that pumps air. When you restrict the intake, you're asking it to do less work, pump less air. That's why the rpms go up: less load. Like a vacuum cleaner when you cover the hose end, rpms go up. It's not the motor straining, it's the motor being happy to do less (until it overheats).
Jim

 

[midcarolina]

OK, Let me re phrase it, when you partially block the intake you can FEEL the increase in air flow.

household furnace type Squirrel cages are designed to run .5 or .8 " above atmopheric pressure. Simply put an amp clamp on the motor running with no intake restriction, make a note of the amp draw then check it with a little restriction.

You will notice with no intake restriction the amp draw will be far less than the rated full load amps IE motor not loaded. now play around with restricting the intake and you can achieve full load amps with maximum air flow............

 

[jimmysisson]

Yep, I agree, there's an amount of intake and an rpm when the motor/fan is most efficient.
Jim

 

[Densleigh]

Hi All,

This is my take on the use of a scrap furnace blower.

I run this at about 1000 rpm on the blower shaft from a standard 540 pto