Manometers

[jsmith]

Hi Guys,

I want to start making some manometers, I am hoping to build to the same spec as the Superflow SF110/120 which flows 185cfm at 10".

I like the look of the manometers that superflow use, but not sure how to go about making them. I figure a plastic syringe could be incorporated but I'm not exactly sure.

Anyone have any good ideas or pictures???

[jsmith]

SF110

[98-1074649673]

The dia of the well will have an effect on the calibration of your upright scale on the vertical manometer. I'd suggest you go with a simple u-tube style manometer and make it the length you need. This can be as simple as a peice of clear tubing. There is some excellent discussion in the archives on manometer design for both the vertical style and inclined manometers.

But, it all comes down to the level of accuracy you want to achieve with your flowbench, do u just want to compare changes or do you want specific readings in inches and CFM's? The latter takes some "thinking" to acheive a level of accuracy.

[jsmith]

[98-1074649673]

Under flowbench links there are links to the old forum's postings. Sorry they are hard to follow sometimes, the old forum was SPAMMED by the Russian porn industry and it crashed big time. This is what I was able to save for reference. If you can't find something or need an explination of something by all means ask away on here!!!

Thats why I run this forum to further everyone's knowledge on this "dark art" I am by no means though a flowbench Guru

[84-1074663779]

Most definitely build a well type manometer, it will be far easier to read because the zero point is fixed and you just read off pressure up a steel tape or ruler.

With a U tube manometer, one leg goes up and the other goes down, and you must read from one leg to the other. This is not too bad for some rough and dirty preliminary blower testing, but later on, for serious flow measurements it will quickly drive you nuts.

Check out the old Forum information, there is a lot on manometer construction as well as how to prepare your own manometer fluid. All really good stuff.

[86rocco]

I'm not positive but I think Superflow uses manometers but Dywer. Anyway, manometers are fairly simple to construct. Here's a pretty primer on manometers. you can find that article and many other interesting related articles on the

[jsmith]

thanks 86rocco, that's a useful handbook.

I agree Tony, I definitely want to build well-type manometers, as you say if the surface area of the well is sufficient (and the manometer bore small enough) then the height drop in the well will be insignificant.

Ok, so basically if my bench is designed to have a test pressure of 10" water, then as I understand it the inclined manometer needs to have a 10" rise over any angle to show a 100% flow reading.

What I don't understand is that the SF110 shown above has a 10" test presure but the inclined manometer clearly doesn't have a 10" rise in height....
how is this possible???

Thanks again.

I did look through the old forum but couldn't find this info.

[86rocco]

[jsmith]

I'm slightly confused then....

If I have a calibrated orifice in my bench which I know flows 160CFM at 10", it is easy to calculate the percentage pressure drop when a test piece is added and transfer that to a 10" vertical drop inclined manometer.

I don't understand how you can transfer to a 6" drop manometer.

If you are testing at 10" there is the possibility of a 10" pressure drop across the cylinder head (however unlikely), if you only have a 6" manometer what will happen...

Am I confused or what.....

[86rocco]

What I'm saying is that the orifices are usually calibrated to 6" or to whatever pressure the inclined manometer is set up to measure, if the pressure exceeds the upper limit of the manometer, a well is placed at the top of the manometer tube to catch the overflowing fluid and return it to the tube when the pressure drops back down again, this is clearly visible on the picture of the SF110 you posted earlier, both the inclined and the vertical manometers have them.

Furthermore, because the percentage scale on a flowbench is non-linear, it's desirable to be testing in the 80-100% range on the scale where it's most accurate so there's very little point in using an inclined manometer that will measure to the full 10" when very little of your testing will be done in the 8-10" range. It's better to use a manometer which has a more limited range and change to a larger orifice when the reading exceeds 100%, that's why there are several different sized orifices on the bench.

[jsmith]

My understanding was:

You design a flowbench and decide what pressure you wish to test at (in my case 10 inches h2o).
You then make some interchangeable orifices or a rotating orifice plate and get them calibrated so you know what you should expect them to flow on your bench at your test pressure (10").
You then make an inclined manometer which has the same drop as your test pressure (10 inches).
You can then create a perentage scale which tells you what percentage of the calibrated flow is flowing at the given test pressure.

So it appears I have got it wrong....

Please explain the process,

I assume that 1st I have to decide the height of the inclined manometer (for example 6"), then I have to make my orifice plates and have them calibrated for flow at 6". I can then design my scale so that I can read off the percentage drop across the calibrated orifice.

Is this correct???

What happens then if I wish to test at 10", how do I calculate the CFM???

I'm getting more confused I think!

Thanks Again

[86rocco]

I think you're confusing the two pressures measured on a flowbench, there's the test pressure (AKA depression), in your example 10", and the differential pressure across the orifice. To test, select an orifice, adjust the air flow so that you have a 10" pressure drop across your test piece then if the differential reading reading on the inclined manometer exceeds 100%, go to the next larger size orifice if it's too low, say less than 75%, go to the next smaller orifice, in either case adjusting the air flow to maintain 10" across your test piece.

The important thing to realize is that since all the air that flows through the test piece also flows through the orifice, in essence, what you are doing is comparing the flow through an unknown test piece at a known pressure drop (10" depression) to the flow through a known piece (the orifice) at an unknown pressure drop as read by the inclined manometer.

So for example if your orifice is calibrated so that there's a 6" pressure differential at 160 cfm and if your test piece flows 160cfm @ 10" then your inclined manometer would show a 6" pressure differential when there's a 10" pressure drop across the test piece and similarly if you are testing at let's say a 28" depression and your inclined manometer shows a 6" differential then your test piece flows 160 cfm @ 28". It makes no difference to the orifice what pressure you are testing at. At any given fixed air flow rate, the pressure differential across the orifice will be the same

I'm trying to be as clear as I can, I hope that makes sense.

[jsmith]

Thanks,

I think I'm getting it!

So basically I need to decide the vertical drop of the inclined manometer (say 6"), and use this to calculate the size of my orifice plate (which will then need checking on another bench for accuracy).

So if I had designed my orifices to show 100% of flow at 6" height then why would I want to test at such extreme pressures as 28" (or would this only be used for really high CFM)?

[86rocco]

I used 28" for my example because that's a fairly standard test pressure, a lot of time when flow numbers are quoted they are a 28".