calibrated orifice plate ?? - orifice plate

[cboggs]

bruce, .. gang,

Got a question, brain teaser, .. etc.

Of the three orifice plates you made for me, ..
I used them on my new flow bench, . but the 400cfm
plate flows 422 cfm, .. and makes a #### of a noise when flowing at 28"

I've checked calibration up one side and down the other, ..
the bench is dead on, . . it's a commercial made bench and was very
well calibrated when I got it. I've flowed several known development
heads in the shop here,.. all dead on.

The other two plates have a smooth sound when flowed and flow
exactly what they should.
The 400 cfm plate sounds like a large air horn when flowed, . so
something beyond my understanding is happening,
and I'd like to understand it.

Got any ideas about this?

Curtis

[dragv6]

I may have no idea but will put somthing down.
What happens if there is a restriction in the flow bench that would couse the figures to be off when the restriction comes into effect at high flow?
Are you using only one size oriface?
Did you try it on your old bench?

[bruce]

Is the plate sitting flat on the top of the bench? Is it being held down by something? The hold-down might be effecting the airflow into the plate? Airleak maybe? What does it do at a lower flow depression?

Just some thoughts . . .

[cboggs]

[larrycavan]

[Thomas Vaught]

Larry,

If Curtis is flowing through a 4.25" "typical Chebby" bore size and the orifice plate for 400 cfm at 28" has a 2.266" orifice then the Beta Ratio is about .28 which may not show up as any difference
vs the flat plate deal. JMO

Tom V.

[bruce]

Ah did you mean 2.361 for a 400cfm plate? 2.266 is only going to give you 368 cfm by my calcs?

[Thomas Vaught]

I plugged in 28 inches and the diameter and looked for 400 cfm using the board spreadsheet, I did not look at the discharge co-efficient, oops!

Either way my only concern was getting a rough beta ratio to see if the diameter was too close to his bore diameter.

Tom V.

[bruce]

Tom, Had me scrambling to do the math also! Wanted to make sure his plates were right cause I'm sure he is using the ones I machined

[cboggs]

[larrycavan]

[gofaster]

Harold Bettis described the SF bench as Ratio-metric and innately turbulent, and went on to say that there some are ranges and test pressures that the benches like better than others.
Your Saenz appears to be constructed a lot like a Blue Bench so maybe your problems with the 400 cfm plate stem from being out of the bench's "comfort zone". I would suggest trying the test at lower or higher test pressures, and compare the results. Maybe the bench would be happier at 25" or 30".

[cboggs]

[Tony]

There would definitely have to be some sort of resonant flow instability, but it is most likely in the bench itself, rather than the test orifice.

Could it be that a particular orifice creates a particular down stream flow pattern that stimulates some sort of peculiar bench resonance effect.

One possible way to fix it might be to line the inside of the bench with soft acoustic absorbent material. That should tend to damp out any resonant peaks, and hopefully prevent a huge buildup of sound energy at a particular frequency.

Or maybe hire your bench to the Coastguard for use as a fog horn, if all else fails.

[cboggs]

The latest deal, ..

still have flow numbers off on the large plate, ..

and my smaller 150 cfm plate is 163, .. so it's a little off too.

I've e-mailed all this to the company, .. as I bought a commercial
bench so I wouldn't have to use my time chasing this stuff, ..

I have also reflowed some of the heads on another bench to find
the numbers on my bench are off, .. I've adjusted the electronics, ..
but it's still not perfict.

A 540 cfm head showed as 568 today, ..

I think this thing is all outa whack, .. ranges off, .. inclined scale off, ..

Now the next question, .. how much will line voltage effect the motors?

if they are 240 motors and I only have 211, .. with 9 motors would that
kill 100 cfm of bench capacity???

Curtis