PTS Flowbench Forum

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.

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

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!

interesting.
i will not bother making radii then.

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)

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.

Brucepts wrote: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.

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

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.

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