PTS Flowbench Forum

You have to build a well to hold your fluid for your incline manometer

Looking at the Flow Bench Calculations spreadsheet,I see where the test pressure (P) is used in the calculations.
If I may ask,what test pressure is used in the calculating,and can I change it somehow?
Am I safe in assuming that if all calculations are being made @28",and I only use 10" or 14",or even the other way around,then results will be off base.My inclined scale won't be correct or anything.

Alan

It will work either way, but there is a trick to it.

In the first sketch the manometer will have the zero at the top of the scale, and the 100% flow graduation at the bottom, many people do it that way and it works fine.

The lower diagram obviously will not work as drawn, because there will be insufficient volume of fluid in the vertical leg to work. But that can easily be fixed by giving the vertical leg a vastly larger bore. In effect it becomes a storage tank, usually referred to as "the well".



If you do it that way, the fluid level in the well hardly changes, and the 100% mark will be at the top of the manometer, which to me seems more natural.
The amount of rise and fall (manometer goes up, well goes down) is proportional to the relative surface areas.
Its very easy to get a very big difference, say 0.125" bore tube, 1.25" diameter well. Area ratio will be 100:1
Is very easy to get several hundred to one area ratio, or even a thousand or more to one is quite practical.

The manometer will rise 16" and the well will only drop by 0.16 inches (same volume of water)

If you do it with an conventional same size bore U tube manometer, one leg goes up 8" and the other goes down 8" which is not as useful as having one leg go the whole 16" with a well.

You can build your test pressure manometer the same way, so the main vertical tube rises the full 28" .

Its pretty simple just a vertical tube going into a bucket full of water would work. Water travels up the tube by vacuum and the water in the bucket has negligible change in level, so you can then use a standard inch ruler directly to measure the test pressure rise.

Ravoll wrote:Looking at the Flow Bench Calculations spreadsheet,I see where the test pressure (P) is used in the calculations.
If I may ask,what test pressure is used in the calculating,and can I change it somehow?
Am I safe in assuming that if all calculations are being made @28",and I only use 10" or 14",or even the other way around,then results will be off base.My inclined scale won't be correct or anything.

Alan

Test pressure is the pressure across what you are testing.
Measurement orifice pressure is the pressure drop across the orifice.

Both are totally independent of each other, but it does often lead to some initial confusion for people new to this.

Flow testing of cylinder heads has become pretty standard at 28 inches. That just means you increase the flow through the head until the measured pressure drop across the head is 28 inches, then measure the flow under that condition.

What you use to measure that flow could be just about anything, but it is quite a separate process to what is going on at the cylinder head.
We use a calibrated measurement orifice, and we can decide to use whatever sized orifice to do that that is convenient. It can have whatever calibrated pressure drop we wish to make it, and that has nothing to do with our choice of test pressure back at the cylinder head.

We can set up our "flow measurer" to have a 10" drop, a 12" drop, a 15" drop or anything else.
Our chosen measurement orifice and chosen manometer rise then work together to read flow through the cylinder head we are testing.

Now we need to think about the incline scale.

The pressure required to force air through an orifice goes up square law.
Suppose one inch of pressure creates a flow of X in cubic feet per minute.
We require four inches (2x2) to create 2X flow
And nine inches (3x3) to create to create 3X flow
And sixteen inches (4x4) to create 4X flow

Looking at it the other way,
If sixteen inches of manometer rise is calibrated for 4X flow, that becomes the 100% flow mark
Nine inches along the scale we can mark off 3X (3/4 of 100%) or 75% flow
Four inches along the scale we can mark off 2X (2/4 of 100%) or 50 % flow
And one inch along the scale we can mark off 1X (1/4 of 100%) or 25% flow

Now X can be any number, say 50 CFM for a small orifice, or 800 CFM for a very large orifice.

But if our 100% flow mark on our sixteen inch rise manometer stays the same it can correspond to either 50 CFM or 800 CFM depending on which orifice we fit into the flow bench.

The percentage flow scale on the manometer stays exactly the same for any sized measurement orifice

All you do is read off the percentage scale and multiply that by the calibration figure for the particular measurement orifice fitted.

If a sixteen inch manometer rises up to four inches, there you will see the 50% flow mark, and if a 220 CFM flow measurement orifice has been fitted, the measured flow will be 110 CFM.

Thanks Tony,
That's easy to understand.16" makes the math easier also . I messed with the Inclined scale compensation spreadsheet,and have a question or two.
What role does the angle play again? I Understood that for a 10" manometer (for example) the highest point should be 10" above the lowest.I entered for 16" scale and vertical height of 8" ,to come up with a 30° angle.Entering a vertical height of 16" to match the length returns 90°.

I see in the scale where the percentages also coincide with 1x/2X and so on,in the Delta s (in) column,but what are the huge numbers in the Delta p (WC in) column.

Alan

There is no need to even know what the angle is !

If you decided to build a manometer scale that was 1,000mm long between the zero mark and the 100 percent flow mark, say for ease of marking off the scale, the tube itself might be perhaps 1,100mm long with some rubber hoses pushed over the ends.

So you screw that to your back board so the 100 percent mark on the scale is exactly 16" higher than the zero mark on the scale, and the job is done.

If you were curious about the exact angle, it could certainly be worked out but who cares !
Its not the angle you are interested in but the length of the hypotenuse (scale length) and opposite side (water rise).

If you decide to use a shorter scale length say 20 inches, or 24 inches or 30 inches or something else, you could. But the high end of the flow scale would still need to be 16" above the low end.
And the steepness of slope would definitely change, although the actual angle required is of no interest.

If you look at pictures on the internet of sloping manometers, there is a huge difference in lengths and angles.
No two are the same, not even remotely similar.
Everyone has their own ideas and needs, and just builds it however they want to.

If you can pick up a ready made flow scale from somewhere, that might determine the tube length, but if not, the choice of both scale length and water rise is entirely open to personal preference.

I do suggest though that you stick with sixteen inches of water rise, if later on you decide to go for the Forum electronic manometer, the transition from water to digital will then be very straightforward as all your collection existing orifice plates will still be usable.

Hi Tony,

I'm still playing with this inclined scale compensation in the flowbench calculations spread sheet.
16" water rise was already decided. I understand the scale also( Delta s) in the center column.The 16" rise is "scale vertical height" and the "scale length" is the Diagonal, pulled out over from 0 to 16 ". The length of the diagonal tubing determines the angle,or the angle determines the length,however one wants to see it.Not that I necessarily want 30 degrees ,but if I did I would need 32" scale length to diagonally cover the 16"vertical height . If I'm understanding things correct,my 16" scale would then be partitioned out over the 32" scale length.25%@2",50%@8",75%@18", and 100%@32". Measure and mark these percentages up or down my 32" diagonal and done.

The reason I was asking about the angle ,is because I see the scale partitioning / resolution varies with variations in the angle /steepness.

What I'm not understanding is the 3rd column.Delta P (WC in) .How does this correlate to the scale height and or scale length?Or is this for something I'm not using?

Alan

I think you are overcomplicating things.

You first need to mark off a scale of a length of your choosing.
Thirty two inches will be fine if that is your choice.

The zero mark and 100% flow mark are to be 32" apart on your new scale.
The 25% flow mark will be (.25 x .25 x 32") = 2.00 inches up the scale
The 26% flow mark will be (.26 x .26 x 32") = 2.1632 inches up the scale
The 99% flow mark will be (0.99 x .99 x 32") = 31.3632 inches up the scale.

The only reason I suggested 1,000mm for a scale length is that for example the 26% flow mark will be at .26 x .26 x1000 = 67.6mm which is pretty easy to find accurately on a 1,000mm steel ruler.

Marking off at 2.163 inches might be a little more of a challenge.

I was thinking about going metric with it also.


So what are the numbers in the 3rd column?

Alan

I am running Linux here not Windows, and that spread sheet does not work on my Linux spread sheet.
As I cannot see the third column I have no idea what it is.