Testing Vacuum Motor Entry.

[Old Grey]

Everyone searches for that extra little performance edge, and when a flow bench guy sees a sharp edge in the path of fast moving air, they think that with some small effort, a radius will make it flow more. So when I saw that the SF-110 uses a big hole, like 3.5", in it's motor plate, but the SF-600 uses small holes, about the size of the vac motor opening, but with a radius, I had to try it. But when I tried it on my homemade vacuum motor radius tester, it didn't flow more.

As you can see, it's just a box with a motor at one end and a SF calibration orifice at the other.






MARK 0.10 - is the bare motor
MARK 0.20 - is 3.5" sharp edge entry
MARK 0.30 - is 3.5" radius entry
MARK 0.40 - is 3.5" radius entry double stacked on 3.5" sharp edge entry - I'm using a double thickness motor plate -
MARK 0.50 - is 45mm radius entry
MARK 0.60 - is 45mm radius entry double stacked on 45mm sharp edge entry
MARK 0.70 - is 45mm sharp edge entry

It's like the velocity is so fast with the 45mm radius, that the air has trouble turning the 90º into the fan blades.

[Brucepts]

Thanks for sharing your testing. I like the motor test box!

On my bench design I simply call out a break all sharp edges as I found it really didn't matter internally on the motors.

If you are looking at those numbers for changes and we are discussing the .0 change I would not be to concerned either, as there are to many variables to think you can get accurate readings at .0 cfm

[Brucepts]

Let me also add . . . testing like this also shows that building a flowbench is not rocket science and does not take any extensive design.

Thanks again for sharing!

[Sir Yun]

interesting.
i will not bother making radii then.

[Old Grey]

I wasn't expect that much improvement, because I read a post where someone only found 0.25", but when it's multiplied by 8 (0.06 x 8 = 0.48"), and the fact I still have to cut the holes in my motor plate anyway, I might as well finalize it because it free flow.

I will be testing other shapes, so maybe I will find something.

I'm new to the FP1, but I wonder why the ACFM doesn't change but the DEP does - they are connected to the same place -, maybe my orifice is too big for this small motor(119655)

[Brucepts]

Your #1 sensor is 100" the way I read your screen shot, you are testing at 5" so you are only using 5% of your sensor which puts it way low in it's range, I doubt it's even picking up any changes in that low of a range. So what you are seeing more than likely is a steady average.

Probably the same thing is happening on the #2 sensor as #2 sensor is a 40" and that puts your CFM reading way low on that sensor also.

[Old Grey]

Your #1 sensor is 100" the way I read your screen shot, you are testing at 5" so you are only using 5% of your sensor which puts it way low in it's range, I doubt it's even picking up any changes in that low of a range. So what you are seeing more than likely is a steady average.

Probably the same thing is happening on the #2 sensor as #2 sensor is a 40" and that puts your CFM reading way low on that sensor also.

Yeah, I'm thinking something is fishy - mainly that I'm doing something wrong -.

I put my hand over the orifice, and the DP(PS1) rises, but the ACFM(PS2) doesn't move at all - if I blow in PS2, it does rise -

Also the motor specs on vacuum are
2.00" orifice, 4.4" H2O, 109 CFM
1.75" orifice, 7.4" H2O, 108 CFM
http://www.rossbrownsales.com.au/files/11965500.pdf

but when I test mine on blowing, it puts out :-
1.878" orifice, 5.4" H2O, 92 CFM (but converted to 28"). with the FP1 set on actual cfm, it's 40.2 cfm.

I think I will have to do some more reading, and maybe make a "U" tube manometer.

[Old Grey]

In round 2, I tried these radius

and got these results

MARK 0.10 - is the bare motor
MARK 0.20 - is a 45mm tapered trumpet ram tube - like on a Weber/inj -
MARK 0.30 - is a 45mm cone with a small 5mm radius at the bottom
MARK 0.40 - is a 45mm with a ½" radius at the bottom of a counter-bore
MARK 0.50 - is 3.5" hole with radius entry - again -
MARK 0.60 - is the bare motor - again -

And for what I can see, the number varies within the natural fluctuation of the system.

So to double checked, and made a new simplified setup

and it pretty much backs up the FP1, because re-testing every radius again, the water column barely changed 1mm - it was 5.41" -.

Tell me if you see something I'm doing wrong

[Sir Yun]

I think that a radius in this position does not take into account where the flow actually goes and as such can not improve it.

I found this

http://www2.lecad.si/education/predmeti ... tavcar.pdf

look at page 48 (closely i might add, it looks like they added a flare and a radiussed edge) and 64.

[vic_dahn]

I work a lot with airflow at my company (R&D fans) http://www.emp-corp.com/products/
a few thing that COULd help

reduce internal vane gap
diffusing the outlet
using straight blades (better for higher DP)

Just because the motor didn't pick up much flow at 0-DP the flow @ ... inches may be more. overall flow does correlate to flow at a certain DP. Just like aftermarket fans just because the fan will flow more at no restriction it may flow much less at an inch or 2 of restriction than a competitor at that same pressure.

I will talk to an engineer that worked with vacuum motors this afternoon and see what he says.
great experiment!

thanks
Vic