PVC tube Flow bench

[dragv6]

Hello to you all from Australia.
I would like some feed back on a design mainly based on the Performance Trends type oriface bench.
The tubing would be 6" pvc pipe.
From my head stock going directly down to a 90 degree turn. Total height is 3 foot 6" .
Then a flow straightner either end of a 8 foot length pipe.
In the middle of that pipe would be the oriface with the pickups either side of it.
Thinking of baffling the pickup holes for better signals.
10 x Amtek motors 109cfm @2". Max amp is 4.8amps. Switched seperatly & one on a variable dial for depression control.
Taking place of the manometers will be 2 x freescale MPX5010dp sensors. I have a Performance Trends datamite 2 datalogger which I can configure to read 0-40wc on the screen until I can aford to upgrade to a full digitalized sysem.
Thanks for your time
Matt
PS please feel free to let me know any possible problems

[SWR]

Virtually identical to the bench I used to use... Only problem I found was that it seemed to drop 5 "additional" cfm for every orifice size I went up,especially as the orifices got so big that they used more than 2/5 of the pipe diameter... In other words, a very accurate SE 300 cfm orifice in a 5" pipe will not give you a really accurate reading. As soon as you get down to pulling,say; 190 cfm through a head,and you swap to a 200 cfm orifice in the same pipe for a better reading on the inclined,it will consistently show you about 196-197 cfm without changing anything... I guess this is because the pipe walls direct the flow through the orifice when the pipe vs orifice diameters become too small. I.e. the 300cfm orifice shows less than it should. I'd go for an 8" pipe if I could fit it.

[dragv6]

That bench design has been dead & berried for me, too much if buts & maybes withe the tube deal.
The new design is two rectangle boxes, one on top of the other. the lower one for the 10 motors & the top being for settling box & oriface.
Thanks for your reply SWR
Matt

[Tony]

I am using a similar two box design myself, and am very happy with the results.

[dragv6]

This is as far as I have gotten

[83-1184962233]

I considered using the orifice in a tube approach last year. The variences you see with the flowrate is due to the CD value changing with beta ratio and reynolds number.
The box design that most people use gives a low beta ratio. The lower the beta ratio the more stable the CD value is for different reynolds numbers (flowrates). A really large box with an orifice in the centre could theoretically maintain a CD of 0.6 over a very wide range of flows.
That makes our measuring much easier.