roots blower as an air mover??

[Beetle]

I have an Eaton M90 blower off a 3.8 litre Buick. is it worth while to use as the air mover for a flow bench? only problem i can see is the size electric motor needed . it displaces 90 cubic inches per revolution. i like the idea because it can suck or blow air.

[Beetle]

I want to build a bench to test air cooled Volkswagen heads. any one worked with them before?

[Sir Yun]

Hi
search! I know there is at least one bench here with pics that was based on a supercharger. very neatly done.

As far as beetle heads go.. I have no experience at all with those

[Tony]

90 inches per rev.
19 revolutions per cubic foot
1,900 rpm for 100 CFM, that would probably (?) need roughly about 1 Hp to drive it.
The blower can obviously be driven much faster than that, but driving it may be the problem.

If you only have single phase power available, single phase VFDs usually top out at around 3Hp, anything larger requiring a three phase mains supply.

Certainly possible for a small bench, but breaking the 300 CFM barrier might be a challenge, unless you have three phase mains power available.
It may also end up being a fairly expensive exercise for the limited airflow possible, unless you can score a free VFD.

[Beetle]

THANKS FOR THE INPUT GUYS!! i have a 230 V single phase , 5 hp motor off an air compressor. turns 3450 RPM i think, have to look at it. So maybe this will work. I will do more searching here on the subject.

[Tony]

Two fundamental difficulties with using a very large single phase motor.

It will typically draw a surge of at least ten to fifteen times rated full load running current when you first apply power. Belt slipping and fuse blowing are very common problems with these motors.

A single phase motor cannot be speed adjusted with a VFD, so it will always have to run flat out at full speed, which is going to be rather noisy and require an air bypass system to control airflow.

I would very strongly recommend using a VFD and a three phase motor.
It solves ALL of the problems very neatly, and it also allows forward/reverse for blow/suck testing, and in the future, fully automatic test pressure control becomes possible.

[Beetle]

i have been doing some searching on CFM info for the Air Cooled VW heads.........might be easier to find a garbage pail full of Hens Teeth!!!!!! but it looking like I only need to flow 200 CFM with stock valve size heads, even the aftermarket large valve heads are flowing just over 200 CFM. so my roots blower idea might just work? was thinking of making a test fixture with the blower and motor connected to and see if it even spins enough. can I make a restriction on the suction side of the box that will be close to the 20 CFM mark to test if it will work at all?? like say a 2" hole with a hole saw? then attach a manometer to the box , see if it will pull 25-28" WC??

[Tony]

Try just starting up the bare motor to begin with. The initial inrush surge current at startup is going to be fearsome.

Then try driving the blower without any air restrictions at all. That condition will require minimum drive power, placing a sturdy protective screen over the blower intake might be a good idea.

Then, as you suggest, fit a suitable orifice restriction to load up the blower, and you can then measure motor current, orifice pressure, and calculate airflow.

[1960FL]

Beetle,

Ok listen to what Tony is saying.. There is math that relates HP to Air watts and this dictates just what the blower can do. The big key here is where you are located US, Canada, UK, etc. and what you have as available Mains service I/E what is the disconnect breaker in your distribution panel ? And how many Amp/Volts can you get to where your bench will be.

Also many VFD’s will do Phase conversion so you could run a 3 phase 3HP motor off a single phase input if the power is available.


Rick

[Beetle]

thanks for the help guys!!! i'm going to mock it up and see what happens?? the blower has a serpentine drive pulley on it...so i need to fabricate a pulley for the motor. these are parts I all ready have lying around....so if it works that is great if not........ill just have to find a car to put the blower on..????
my shop and house both have 200 amp service, both single phase though. it will be a great experiment if it works or not.
i did some math and i need to over drive the blower ( just over 1.0:1) to get it to pump just over 200 CFM, which is all i need.
i planned on going with the orifice plate design for it's simplicity. how many plates do i need and what size to get to my 200 CFM max flow or possibly just a tad higher to be safe? i also will be useing water manometers to start out and move up to digital ones down the road.