Manometer Scale & Orifice Calculations

[86rocco1]

[106-1194218389]

Thanks Ed,
I had a friend looking over my shoulder once when I was perusing this forum. All he could say was "Man alive! These guys are all "Brainiacs"! How can they think this stuff up?" He was really impressed by all that goes on here. He was really blown away by your spreadsheets. When I showed him what was being done with the DAQs he was just left gasping. He could not believe just a bunch of guys do this. That is when I had to say "I am Borg, I am part of the Collective" He was a little nervous until he saw me smiling at him. Anyway, this is great stuff. Ed with all the help I was able to build me an $1100.00 inclined manometer for $25.00 :;):
John

[86rocco1]

You're welcome John.

That'll be $1075.00 please :laugh:

[106-1194218389]

[resbum]

[color=#000000]Gentlemen;
Right off the bat let me say, I am new to the flow bench scene, I will also say that after spending some time on this site, I believe there is no better place for me to learn about flow benches. Bruce, this is a great forum and thanks for the help you already have provided.
So now I am beginning to put a cabinet together, I have acquired some gauges and a sweet digital flow meter. From the moment I made the decision to do this I decided NOT to use manometers.

1. Because I knew nothing about them
2. There are so many corrections to apply (angle, fluid, tube size etc etc)
3. Because I know nothing about them.

I felt the learning curve was too steep, so I went with Dwyer gauges.
I have a 603A-6 Digital Read-out Differential Pressure Transmitter and a 5100 analog differential gauge both of which I will connect to either side of the orifice. They display up to 100 in. H2O.
To monitor the pressure at the test piece I have a Dwyer 5040 gauge which indicates 0-40 in H2O.
This seemed like a good plan to me, I could read inches of water depression right off a gauge. A gauge I had confidence in vs. a manometer I constructed and had little or no confidence in.
Today I was looking at some posts about Excel Spreadsheets and computations to calculate CFM.
I don

[bruce]

[bruce]

I think people make the water gauge build harder than it needs to be, if you look at all the variations of water gauges that have been made and used here on the forum you will find they are pretty accurate.

Ed's spreadsheet does all the math for you, yes it has a lot of numbers on it and some can be confusing to the first time flowbench builder (and some of us old-timers also) but if you follow some of the old posts here on the forum (or ask the ??'s again) you will find it really is simple to build some seriously accurate water gauges using some simple materials.

Personally, I'd feel more confidence in a homebuilt water gauge than some dial gauge of unknown origin. How do you know the dial gauges are accurate?

Which ever way you go with your flowbench build someone here will be able to answer your questions as they come up.

[86rocco1]

The nice thing about liquid filled manometers is that once they're properly constructed and set-up, nothing ever goes wrong with them. They're immune to mechanical and electronic problems, no other pressure measurement device can make that claim. I plan to get digital gauges but I'm keep the liquid filled manometers too just as a back-up and a means of double checking.

[resbum]

I admit it may not have been the best descision and now I think I will have to man up and have a fluid manometer too. But my question remains. When I begin to calibrate my set-up, what values do I use when using gauges vs. a manometer?

And Bruce, if I haven't kicked this project to the curb in a month or two I will upgrade to your digital manometer. I have very little money in this project so far, I would like to keep it that way until I am convinced I know what I am doing.

S.P.

[bruce]

[jfholm]

Steve,
This really is quite easy. With your digital gauge that you are going to use for testing the pressure differential on either side of the test orifice, decide on the length you want to use and leave it there. Say 36" of 100" or what ever.

Then download Ed's spreadsheet for the inclined manometer calibration. Now I have already checked this out so I know it works. The only thing you need to worry about as far as input data is the length of manometer. Input that and you will see the scale conversion to percentage.

Then when you read your digital gauge and it says 9" H2O (if you set your length to 36") you would have a 50% flow reading of what you orifice is calibrated to.

I am still trying to think of how to determine the Dp of the orifice. I know how to calibrate it to use with my water manometer. Is there a setting on your digital that asks for Dp (Delta P)?

Asking for help from others here, do you just test the differential pressure at the test pressure and that is your Dp? i.e. you run test pressure up to 28" and if you differential at the orifice is 16" H2O then your Dp is 16" H2O. ????

John

[resbum]

[Ted B]

Hi there,
My flow bench is about 1/2 done. I was looking at the calculation sheet because i've been wondering about the density of air. Once i get my flow bench calibrated and up and running, how do i account for different air temperatures and humidity in my calculations? Does it matter very much? If not ok. If so, is there a calculation sheet for normalizing readings to a standard value?
Thanks
ted

[thomasvaught-1]

Because the PTS Benches are "Ratiometric" Benches (like the Blue Bench) the bench will be accurate whether it is at Death Valley, Denver, or in Tampa, Florida ONCE the bench is calibrated using one of Bruce's inexpensive Calibration Plates.

The Spreadsheets a given weight of the air which would affect the "Mass Flow" calculation but we are using "Volumetric Flow" reading and the "Test Part" and the "Orifice Plate" are seeing exactly the same ambient conditions fractions of a second from each other during testing.

Hope this helps.

Tom Vaught

[Ted B]

I'm not sure but i think by the term ratiometric you're saying that in the calculation sheet we're looking at the comparative density of the air to the manometer fluid (water) so in this case small density changes in the air density due humidity, barometric pressure or temperature will have a very small effect. Am i on the right track?