annubar construction - need help

[slr350]

im building a flow bench and need a little more info on annubars.
When using in a long 2 inch pipe what size tube should i use to make the annubar and what size holes should i drill?
I was thinking of soldering 2 tubes together ( one pressure, one static) and drilling holes in each tube so i can reverse the flow and get a reading, would this cause a problem?

flow
l " l
l 8 l soldered tubes
l " l
Any help in constructing an annubar or simple pitot tube set up would be much appreciated

[bruce]

I'll add a little info to help you get started. I use 1/8" tubing, holes are drilled in the face based on a standard formula for duct traversing verses inside pipe dia. I hold these dimensions extremely close (read within a thousand or two) on my milling machine. The dia of the holes are less than .062".

You have to make sure the holes are facing into the airflow, so if you solder two back to back they must be exact. I have found it easier to have 2 annubars one facing intake flow and one facing exhaust in past concept testing. Now I just reverse the direction of my one annubar and blow back through the bench or draw the flow in through my exhaust port. The static pickup is just a hole flush with the inside dia of the test pipe.

This is just what I have found works quite well, not saying its the only way to do it and would like to hear feedback on how your setup works if you do the way you suggest?

Ok now you got me "brain storming" Heck might even make a flowtube up swap it out with the one I have in my bench now to test it out for myself. I could compare the readings to what I use now. Would they have to be soldered back to back or could they just be located close to each other? I guess a setup could be made and tested on the top of the bench and compared to actual flow numbers through the existing flowtube? Any ideas?

[slr350]

I found this annubar that uses slots on a flat surface with the static holes below, this is where i got the idea of joing 2 tubes together.
Heres the link for the PDF doc

[bruce]

I guess it all comes down to how much time you want to spend making the parts? I have found that the annubars made the way I make them work quite well and give accurate repeatable readings. Now don't get me wrong, I'm not saying my design is the only way to make them and I enjoy "new thinking" but I also like to play the devils advocate and ask why?

One could spend all sorts of time re-engineering annubars if thats all one produced, but isn't it about getting a working flowbench up and running with a certain level of repeatability and accuracy? A peice of tubing with a 90* bend in it is probably the cheapest way to go, and you would be surprised how accurate it is. The annubars I make are simple 1/8" tubing (which anyone can purchase) with accurate drilled holes based on HVAC industry standard traversing locations (information available on the web). This traversing averages out the flow across the width of the flowpipe where as the single hole only takes one reading.

Here again I'm not trying to stunt anyones thinking, nor try to sell my annubars (I'm sure not making a living selling them . . . yet anyways ). . .

[maxracesoftware]

Bruce , how much $ are you selling your annubars for ?

[bruce]

A complete listing of what I offer for the home DIY'er in the way of flowbench parts is located here on my website:

My annubars are priced at $10 each and fit standard PVC Sch 40 pipe (white PVC sold at local stores)

I also make orifice plates and I just picked up some thin stainless steel tubing .062 dia and smaller for making velocity probes.

My parts are made for the homeshop person who does not have the $$$'s or equipment to buy or make their own and wants to "play" with a flowbench. These parts coupled with the knowledge on this forum and you are on your way to a very repeatable flowbench. I have a few happy customers with my parts in service . . .



Edited By bruce on 1097890147

[slr350]

Thanks for the advice Bruce, Man i would love to buy your parts but im in Australia.
I had a go at making somthing similar to the rosemount annubar but it ended up to big and would have been a big restriction. I might stick in the 3 inch tube section just to see if it works.
So i decided to go with your type. Its not as well made as the ones you produce but with any luck it should work. I used the standard traversing locations as you mentioned with 1/8 tube.
I should have it up and running tomorrow with a bit of luck and get into some testing.

[gaz]

Almost everything here makes sence. The only thing I didnt understand was about static pressure part --"The static pickup is just a hole flush with the inside dia of the test pipe." If its taken the same way as the static test pressure(28"H2O) then what diametre hole would be the best for 2" PVC? and for the test pressure hole also:)?

[bruce]

I use a #58 drill which is .042" for my static pickups

[gaz]

would it be too bad if I made an annubar out of 0.16 inch OD tube and 0.062 inch holes in it?
How do you guys turn the little holes exactly facing the airflow or isnt it THAT important?
Thank you all.

[bruce]

I simply make a mark inline with the holes on the part of the annubar that will be outside the pipe. You then use this as a reference for locating the holes inline with your flow. A few degrees or two one way or the other does not effect your readings I have found. If you have a single hole pitot though facing into the airstream it will be effected more than an annubar design by not being inline with the flow. Another way would be to turn the annubar one way or the other while watching the flow for a drop in your readings. This is how I first did it when I played with my initial annubar and pitot ideas.

I would not see why your dimensions would not work for your annubars. I would try and keep my holes as small as possible along with the dia of the tube, but thats just my opinion. Your sizes should give you good readings. Here again its about repeatability between tests.

[AM91Camaro_RS]

i know that this is a little old but i'm at this point now. i'm trying to get my inclined manometer to read right and so far i'm pretty sure that it isn't. my 'test pipe' is 2.5" pipe and about 4.5 ft. long. i'm using 1/4" OD tubing for my manometers, U-tube and inclined. does this sound okay? i think i'm going to try to make an averaging pitot tube like yours, bruce. i'll use 1/8" tubing with some tiny holes like yours and see what happens. can the static hookup just be in the test pipe right by the averaging pitot tube? thanks for all your help!

[bruce]

You're on the right track! I keep the static pickup within a 1/2" of the averaging pitot tube location. I found this works the best for accurate readings.

[AM91Camaro_RS]

awesome, thanks bruce. one more question... i assume that the static pickup hooks to the 'top' of the inclined manometer and the averaging pitot tube hooks to the 'bottom' of the inclined... am i right?

[bruce]

All depends on which direction you want the fluid to flow in the manometer. Static on the top, flow would go up, static on the well, and flow would go down. I have mine connected to Mouse's Flow Processor so direction of flow is not an issue for me