Page 1 of 1
Posted:
Tue Jul 18, 2006 11:39 pmby jsa
I've been considering ways of measuring large flow ranges with pitot's as I think I need 2 pitot's to cover 10-1000cfm range I'd like to do on my bench, but want to avoid the complexity of switching and so on.
I am thinking it might be possible to have a single pitot, and an additional bleed passage in parallel.
For low range the bleed passage is blocked. For high range the bleed passage is open.
Would the bleed passage and pitot flow proportional amounts of air ?
If so then a simple correction number would be applied to give total flow.
Anyone tried or got thoughts on this ?
Posted:
Wed Jul 19, 2006 1:18 pmby bruce
I'm not following along with how you plan on using the pitot? Maybe a picture/drawing?
Why would you need a bleed passage?
Posted:
Wed Jul 19, 2006 7:46 pmby jsa
Posted:
Wed Jul 19, 2006 9:45 pmby 2seater
The theory is probably sound, essentially indirect flow measuring. In practice it may be different as flow rates and air flow patterns possibly change. The only way to find out would be to test it with another flow device that would measure the total flow and see if the relationship remains constant, at least at several test flow rates. The MAF on my car works somewhat as you suggest. There are two flow passages, and the smaller one contains the actual sensor. The total flow is calculated but only a small portion is actually measured directly.
Posted:
Wed Jul 19, 2006 10:04 pmby bruce
Ok ,now my next question would be why do you need to limit yourself to one pitot? Is cost a factor? (pssst . . . you can buy 3 different sizes of my averaging tubes for less than the cost of one commercial pitot probe, and tests show they are just as accurate if not more accurate)
Are you going with water manometers or digital? Digital will extend your range depending on what system you purchase. (Hint look at the FP1 setup)
I'm not discounting your ideas/thoughts on a second tube, I'm always open to new ideas, that is what the forum is all about 
Posted:
Wed Jul 19, 2006 10:32 pmby jsa