are my fan choices too big ?

[Tony]

righty ho ,
well the iron case fan is an approximately 10 inch wheel ,and had a 3.33:1 ratio step up ,so it on a 2820 rpm motor so will be doing 9390 rpm .wow ! that seems a lot .

Another way to look at this is, 10 inch wheel x 3.33 is same tip speed as a 33.3 inch wheel at 2820 rpm.

I would say you might be looking at around 55 to 60 inches of pressure.

[ivanhoew]

thanks tony ,that does put concisely .

so i managed to get to the magic scrap yard today , and unearthed the paxton blowers , i measured very approximately the pulley on the drive motor and the specs ..

its a 3450 rpm 15 hp ,pulley dia 11.8''. the pulley on the paxton blower is 1.57''..so 7.5:1 ratio .so 25,875rpm!!! OOOOOF!!

wth 6.7'' wheel,this equates to 756 fps. so way way more than my other one at 409.5 fps.


(edittted to change motor speed to correct rpm ).

[Tony]

That sounds similar in concept to a Vortron industrial blower.
These are a cousin to the well known Vortech supercharger range.

http://www.vortron.com/blowers.htm

These things are awesome, up to 150 inches, and vast CFM too.
A Paxton should be o/k to run at those rpm, the bearings and balance will be up to the job, if it is still in reasonable mechanical condition.

Superchargers make superb flow bench blowers if you can score one somewhere.
Usually good ones are up out of the price range of many of us.
One to two psi of boost is a walk in the park for a supercharger, and that is 28 to 56 inches of pressure.

[ivanhoew]

perhaps i sohuld go down there and buy the rest of them !!lol
something of interest , is that i was told they may have come off a us submarine ,as the air change fans ..i now notice the motor speed is that 60 Hz us supply frequency.

also of interest is that looking at that link ,one could run it at 14k rpm ,and still get 1 to 3 psi out of it !

[ivanhoew]

its a runner !

http://youtu.be/eL6SauqdI6k

nice .cabinet making will now ensue .

[Brucepts]

Looks like the start of a new flowbench build!!!

Always like to see a new style being built

[ivanhoew]

good idea bruce ,i wil start a thread .

[Tony]

A "baseline" pressure measurement for a 50 Hz motor (maybe 2,850 rpm) with an eighteen inch rotor would be about 17 inches water (completely blocked flow) and perhaps 16 inches water working with some reasonable flow.

A ten inch wheel at the same 2,850 rpm might work out 10/18 x 10/18 x 16" = 4.94 inches working pressure

Add a 3.33 pulley step up in speed 3.33 x 3.33 x 4.94 = 54.8 inches pressure at "reasonable" flow.
Working like that, I would anticipate about 65 to 70 CFM per motor horsepower.
I would also expect to see closer to 58 inches with the flow completely blocked.
I will be fascinated to see how close my guess turns out.

That is going to make a beautiful flow bench blower with a VFD.