Yes, I am full of questions this week! LOL.
Ok, I read somewhere (maybe the Hyperflow book) that there is a reason the inclined manometer is not a straight scale based on % of flow. What I mean is, even though you are at 50% of the indicated scale, it is not a true 50% reading (50% of full scale). And the scale is much closer together at the bottom end.
What my question is, how do you determine the "correct" % of flow scale. I think it has to do with the weight of the water as it moves up the scale???
Second question is, why use a 28" incline? What is keeping you from doing a 14" or even a 10" incline with the same total length (more resolution)?
What I am planning (since I do small engine stuff) is to use a 10cfm, 20cfm, 40cfm, 60cfm, 80cfm, and 100cfm orifices since that is the range we work in most with our stuff. Keeping the split between the orifices small, I'm thinking I can use a shorter rise in the manometer but with the same length and get better resolution through the % of flow. Am I way off base here? How do I determine with those orifice sizes what incline I need to stay in the 60%-90% range?
Thanks guys!!!!
Inclined Manometer
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by 84-1074663779 » Wed Apr 14, 2004 7:26 pm
Hmmmmm, difficult to put into words.
Any manometer works by pushing fluid up a tube, and it reaches a level depending on the applied air pressure. But the fluid that goes up the tube must come from somewhere.
For instance with a standard U manometer one leg goes up, and the other leg goes down by an equal amount. So you must measure the total difference in fluid height from one tube leg to the other. You could just measure the rise in one leg with a ruler, but the pressure would actually be double what you measure in that one leg, because the other leg has dropped an equal amount. (if you know what I mean).
If one manometer leg was vertical and the other leg sloped at some angle, you would get the same effect, but it would not be so simple to work out what was going on. You cannot just measure the fluid rise along the sloping portion as the total pressure reading. You could make a special scale calibrated in inches of pressure or %flow, but an inch of pressure would not be an inch of rise along the scale. But it could be done that way with a specially corrected scale.
A better way to build any manometer is to make a well type manometer. Here there is a large reservoir with a very large surface area. Imagine a bucket full of water. Dip one end of your manometer tube in the bucket and suck some water up the tube with a negative pressure.
The water in the tube rises, but the level in the bucket falls only a minute distance. So if your well is big enough you can then measure pressure directly with a true inch scale next to the tube.
The same thing can be done with a sloping manometer. If your well has enough surface area you can ignore any change in fluid height change in the well, and assume the zero point does not move. It is not difficult to make your well surface area 1000 times your manometer tube internal area.
But your well might only have ten times the tube area, better than nothing, and you are still going to need a corrected scale. Some of the commercial manometers have a well that looks like a syringe body. If you are making your own manometers, do not be stingy, build a decent well for it, and you can then use a stainless steel ruler or measuring tape at least on the test pressure manometer.
With a sloping manometer the actual pressure rise is going to be referenced back to the fluid height in the other leg or well, and this must be taken into account.
Any manometer works by pushing fluid up a tube, and it reaches a level depending on the applied air pressure. But the fluid that goes up the tube must come from somewhere.
For instance with a standard U manometer one leg goes up, and the other leg goes down by an equal amount. So you must measure the total difference in fluid height from one tube leg to the other. You could just measure the rise in one leg with a ruler, but the pressure would actually be double what you measure in that one leg, because the other leg has dropped an equal amount. (if you know what I mean).
If one manometer leg was vertical and the other leg sloped at some angle, you would get the same effect, but it would not be so simple to work out what was going on. You cannot just measure the fluid rise along the sloping portion as the total pressure reading. You could make a special scale calibrated in inches of pressure or %flow, but an inch of pressure would not be an inch of rise along the scale. But it could be done that way with a specially corrected scale.
A better way to build any manometer is to make a well type manometer. Here there is a large reservoir with a very large surface area. Imagine a bucket full of water. Dip one end of your manometer tube in the bucket and suck some water up the tube with a negative pressure.
The water in the tube rises, but the level in the bucket falls only a minute distance. So if your well is big enough you can then measure pressure directly with a true inch scale next to the tube.
The same thing can be done with a sloping manometer. If your well has enough surface area you can ignore any change in fluid height change in the well, and assume the zero point does not move. It is not difficult to make your well surface area 1000 times your manometer tube internal area.
But your well might only have ten times the tube area, better than nothing, and you are still going to need a corrected scale. Some of the commercial manometers have a well that looks like a syringe body. If you are making your own manometers, do not be stingy, build a decent well for it, and you can then use a stainless steel ruler or measuring tape at least on the test pressure manometer.
With a sloping manometer the actual pressure rise is going to be referenced back to the fluid height in the other leg or well, and this must be taken into account.
- 84-1074663779
by 102-1081363915 » Thu Apr 15, 2004 9:09 am
Good info Tony. I guess I should have been more clear of what I was asking though. I know how manometers work. I have a pretty good understanding of everything you posted. However, I do NOT know how they "progressive" sliding/slope scale is come up with for the inclined manometers similar to the Mercdog68 or the Popular Hotrodding flowbench. It is not a linear scale (numbers same distance apart from start to finish).
What I am saying is I want to make my own scale because I do not want to use the 28" inclined manometer like they are using. I am looking at using something more like the "hyperflow" bench that uses a 36" long scale but only uses a 4.5" rise. They have a %flow "chart" that goes along with the scale, I just want to know how to come up with that %flow from the indicated scale.
Thanks!
What I am saying is I want to make my own scale because I do not want to use the 28" inclined manometer like they are using. I am looking at using something more like the "hyperflow" bench that uses a 36" long scale but only uses a 4.5" rise. They have a %flow "chart" that goes along with the scale, I just want to know how to come up with that %flow from the indicated scale.
Thanks!
- 102-1081363915
by 86rocco » Thu Apr 15, 2004 10:39 am
It's a simple squared relationship, (%flow)^2* length of tube will generate the scale for you. I've attached an excel worksheet just plug in the length and height of your scale, the diameter of your tube and reservior (it assumes a cylindrical reservior) and it will compute the scale and the pressure differences.
- 86rocco
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- Joined: Fri Mar 12, 2004 9:11 am
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