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Posted:
Tue Apr 15, 2008 1:23 pmby DWC
Hi all,
I have a question regarding something i read in a friends superflow 300/600 manual a couple of weeks ago and it refers to the test pressure you test at. I think it said something like the 300/600 benches are calibrated at 25" of test pressure and if you test at a differant pressure than that you are to correct your numbers by a correction factor. I cant remember the numbers right now but why is this so? Does anyone have any thoughts or comments on this.
Darrin.
Posted:
Tue Apr 15, 2008 4:18 pmby 86rocco1
Consider this, suppose you're blowing air through a hole in a piece of sheet metal, if you increase the pressure, you're going to increase the amount of air that flows.
So, for a flow measurement to have any real meaning you must specify the pressure at which the flow was measured. Superflow chooses to do that at 25", there's nothing inherently special about 25", it's just the number they chose for their specification.
Now, in order make a reasonable comparison between one flow measurement and another, they need to be referenced to the same test pressure so that you're comparing apples to apples as it were, it's nothing more complicated than that.
Posted:
Wed Apr 16, 2008 10:14 amby DWC
Ok i think i had better expand on and clarify my question a little more. What i was refering to was the cfm value they are giving to each of the flow ranges. I will type what they have written in their manual.
Important note: The SF-300/600 flow ranges are based on a test pressure of 25" of water. If other test pressures are used, the flow scale calibration ranges should be corrected by the following amounts.
test/pressure intake flow
48" 0.978
36" 0.989
28" 0.997
25" 1.000
20" 1.005
15" 1.010
10" 1.014
5" 1.019
example: the calibration range for #4 is 300 cfm @ 25" of water test pressure. If you wish to test @ 36" test pressure. The corrected flow scale range is 300 x 0.989 = 296.7 cfm.
So based on this i am thinking that they are saying that the cd value of the orifice in the bench changes based on the test pressure your using. The reason i think this is because the orifice for the respective flow range has not changed size and the delta p has not changed. 100 percent on the inclined manometer is still 6" of water column pressure difference across the orifice at least thats the case with the SF300 bench. So the only other variable i was thinking was the cd of the orifice has changed the cfm value of the orifice. What do you guys think?
regards,
Darrin.
Posted:
Thu Apr 17, 2008 9:04 pmby larrycavan
Posted:
Thu Apr 17, 2008 9:08 pmby bruce
I wonder how much this has to do with square versus sharp edge plates? ???
Edited By bruce on 1208480901
Posted:
Thu Apr 17, 2008 9:12 pmby larrycavan
Posted:
Thu Apr 17, 2008 9:19 pmby 106-1194218389
I think I posted this when post flow tests with my new bench. I use square edged orifices right now and I originally was flowing at 6" and let Port Flow Analyser automatically convert to 28". I then started flowing at 10", now that is only a 4" difference, and I still let PFA convert to 28" and is shows a little more CFM by flowing at 10" and converting to 28". That is one reason I am so anxious to get more motors and flow at 28" at least. btw Bruce, are those Surplus Center motors bushed bearings or ball bearings?
John
Posted:
Thu Apr 17, 2008 9:28 pmby bruce
Posted:
Thu Apr 17, 2008 11:25 pmby 106-1194218389
Posted:
Thu Apr 17, 2008 11:33 pmby bruce
Posted:
Fri Apr 18, 2008 6:56 amby larrycavan
Posted:
Fri Apr 18, 2008 9:52 amby 106-1194218389
So the flow path through the motors is horizontal and not vertical? The impellor shaft is horizontal is what I am trying to say but in my old age words come slowly anymore.
John
Posted:
Fri Apr 18, 2008 10:41 amby DWC
Posted:
Fri Apr 18, 2008 10:01 pmby larrycavan
Posted:
Sat Apr 19, 2008 2:59 pmby DWC
Larry,
With regard to delta p all very clear and you explained it well and yes there was a curve to that ball as i was only refering to the 100% value of the of the inclined manometer.
Also not sure of my line of thought now with your bench working opposite but i take that back your 100% correct i sometimes do that look at something backwards there is probably some medical term for me. (LOL) Anyhow thanks for your input.
Darrin