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Posted:
Sat Feb 18, 2006 6:00 pmby blown928
I added an inclined manometer this afternoon but it's not working. What did I do wrong? I can set the vertical mano to 28", it's sucking like crazy through the head, blowing like crazy through the exhaust flow element, but I only get a couple of inches on the inclined mano.
I plumbed from the static port to the high side of the incline and from the averaging pitot tube to the well then to the low side of the incline.
What did I do wrong here? Do my averaging pitot tubes suck that much? I know they're not perfect but I thought I'd do a little better than THIS!
I remade one of them because the holes were so far off, and it came out much better. I'm using the best of the 3 in this first test. Where did I go wrong?
Posted:
Sat Feb 18, 2006 6:23 pmby bruce
Are the holes in your tubes in exact alignment from top to bottom? If they are not, you will not be reading the correct velocity. When I machine my averaging tubes they are done in a milling machine to keep them in an accurate line.
Where did you take the static pickup for the inclined manometer? This needs to be taken from the same location as the pitot . From my testing I have found you will get false static readings on your inclined manometer (within 1/2" in front of the pitot was what I found to work best).
Edited By bruce on 1140301620
Posted:
Sat Feb 18, 2006 6:31 pmby blown928
No, the holes are not in a perfect line. That's why I remade one, because the holes were so far out of whack. The one I used was 'pretty good' but still not perfect. I expected it to be better than this, which is giving me almost nothing for a reading.
The static port is 1" before the averaging pitot tube.
Posted:
Sat Feb 18, 2006 6:35 pmby bruce
Not enough velocity in the 3" tube for what you are testing would be my next guess. Try making one for a 1-1/2" or 2" tube.
Posted:
Sat Feb 18, 2006 7:45 pmby Tony
Agree with Bruce, you either need to increase air velocity through the measurement section (by reducing the diameter), or reduce the slope of the manometer so the high end is perhaps only two inches above the low end.
Either approach would work, but it is a case of deciding which way to go.
Posted:
Sat Feb 18, 2006 8:01 pmby Thomas Vaught
Your reservoir for the inclined manometer looks like it is too high vs the zero point (hopefully the bottom right side of the incline scale). I am assuming that the reservoir is filled to about the black mounting band on the white reservoir. This would be several inches above the scale zero point. I also know that the reservoir is too low to be the high point on the scale like a dwyer manometer.
Check it out and post back more info.
Tom V.
Posted:
Sat Feb 18, 2006 9:02 pmby blown928
Posted:
Sat Feb 18, 2006 11:51 pmby blown928
Tom, if the resevoir was filled a couple of inches above the zero point on the incline it would push the fluid a couple of inches up the incline. Am I missing something here? How would you zero the fluid this way? Is there something wrong with the way I have the resevoir wrt the incline?
Posted:
Sat Feb 18, 2006 11:56 pmby blown928
Tom, if the resevoir was filled a couple of inches above the zero point on the incline it would push the fluid a couple of inches up the incline. Am I missing something here? How would you zero the fluid this way? Is there something wrong with the way I have the resevoir wrt the incline?
Posted:
Sun Feb 19, 2006 12:09 amby blown928
Posted:
Sun Feb 19, 2006 7:43 amby 86rocco
Posted:
Sun Feb 19, 2006 10:35 amby Mouse
2" total pressure in a 3" path = 260 cfm.
Edit: Opps, that's 287 cfm, with an average TP of 2".
John
Posted:
Sun Feb 19, 2006 10:44 amby blown928
Of course you guys are right. Once I look at the numbers it starts to add up. PVC is measured by the ID, I measure the 3" pipe at 3.035". 2" up the incline = 0.5" WC which plugged into the spreadsheet (thanks again, Ed) works out to 141 cfm. A little higher than expected but in the ballpark given the inaccuracies that low on the scale.
Thanks guys, now back to the shop to play a bit more.
Posted:
Sun Feb 19, 2006 12:01 pmby Mouse
Opposing Pitot tubes will create a stronger signal.
I highly recommend electronics for Pitot tube applications.
John
Posted:
Sun Feb 19, 2006 3:33 pmby Thomas Vaught
Nothing wrong with your reservoir deal. Was had to see where the zero line was on the scale.
Having the fluid at the lower end of the reservoir is only an issue if at full scale you get into the tapered part of the reservoir vs the vertical part.
Tom V.