What size ranges - trying to decide what size tubing to use

[Griffin]

So we're leaning heavily towards Pitot tube and FP1, and so we're trying to decide how to set up our ranges. (the goal is 800 CFM)

I saw Bruce's setup with the swapable sections which is cool, but we were thinking we'd like to just go with permanantly fixed tubes. I was thinking it would be nice to have one each of a 4", 3" 2" and 1.5" but I don't know how necessary it is to have 1.5" (or anything under 2" for that matter) and I also don't know if we could just get by with 4" and 2" or whatever.

I was hoping some of you that have already been there and done that could shed a little advice on the best choices.

Thanks!

[larrycavan]

If you have to swap pipes in and out for range accuracy then I fail to see the advantage of pitot over orifice. I'm sure someone will disagree with that.

800CFM can be achieved through a reasonable sized orifice.
A 3.490" orifice with a .62Cd @28" pressure differential is good for 874CFM [providing you have enough motors to pull hte depression]

3 orifices, 1.5", 2.5" & 4" would cover a wide spectrum, can be individually calibrated for bi-directional flow characteristics and IMHO be far easier to construct.

A 4" orifice with .62Cd @28" pressure differential will achieve beyond 800CFM.

Larry C

[trader]

Griffin and others, here is a link to a good tool to determine differential pressures for any given flow in a (sch 40) pipe size, using a DS - 200, 300, 400 series sensor (averaging pitot tube). The 200 series are no longer available, with the exception to e-bay. The choice is not only a consideration of the high side of the flow region, but also the low side. eg. the low side of the range for a 1" pipe is 4 scfm @ .1" dp, where the 4" pipe is almost 60 scfm @ the same .1" dp. (testing @ 14.696 psia) Another problem is that these sensors have a flow region, where continuous operation may cause vibrational damage to the flow sensor (Dwyer bulletin F-50). (they are only anchored on one side of the pipe) A little time playing on this calculator, will reinforce the value of a FP1 or a digital manometer in opposition to an incline water manometer, when you read the differential pressure on the results page....trader

[trader]

This chart might help also. It is for a DS-200 series sensor. I have not been able to link to it online, so I will post a scan....trader

[larrycavan]

[Thomas Vaught]

We use Flow Nozzles or Venturis to measure flow when we do not have a demand for a specific test pressure but still want cfm. The Ford bench as was mentioned is a venturi bench.

The issue comes up naturally when everyone wants to quote figures at 28" of water.

JMO

Tom V.

Bob Mullins developed some very high hp hemi cylinder heads with fairly low test pressures (< 5" of water).

[bruce]

[larrycavan]

[Griffin]

[trader]

Griffin,

Static line pressure is computed from this formula: A.P. + PSIG = PSIA. Barometric Presure (in psi) + psig (guage test pressure) = psia (absolute). The barometric pressure varies by the altitude where you live, but is generally considered 29.93" Hg, and normally referred to as 14.7 psi. So if

1"wc = .0361psi = .0735" Hg = .2489 Kpa....

10"wc = .3609 psi = .7348" Hg = 2.488 Kpa....

28"wc = 1.010psi = 29.93Hg = 6.964 Kpa....

14.7psi (A.P.) + 1.010psig (28"wc test pressure) = 15.710 psia

14.7psi (A.P.) - 1.010psig (28"wc test depression) = 13.690psia


Heres a Link to the pressure conversion chart to save to your hard drive or print it out. On the bottom of the DS calculator page is a link that allows you to download an excell spreadsheet that has 2 pages. All you have to do is fill in the cells, and it is more user friendly than the other calculator. You will have to have info from Dwyer bulletin F - 50 to use it. This Calculator is for the use of the DS sensors and not a general guide for the pitot.... trader

[Griffin]

Thanks!