Orifice vs calibration plate

[SuperRunner]

I am wrong in thinking that a 2 inch calibration plate with a 2 inch calibration plate show 100% flow?

Right now I have a 2.1" orifice with a < 2.1" calibration plate, but at show well over 100% flow. Probably more like 120+% flow. What gives?

[larrycavan]

When you say it's flowing 120%, how are you measuring that?

If it's with an inclined manometer, how are you calculating the additional 20% beyond 100%?

[SuperRunner]

That is just a guess, but now that I think about it, with the scale the way it is, it is probably less than that. But I have a U that drops down about 3 inches, and it will suck all the fluid into the reservoir.

I have even tried a 2.5" orifice with a calibration plate that is only supposed to flow around 250cfm at 25".

For a leak test, I use a 2.1" orifice and ran it up to 28" cfm. The scale actually went up about -5%

[bruce]

What are your exact dimensions on your plates? Are your plates exactly 2.100" Is each plate machined exactly the same?

[SuperRunner]

one of them is 1.96 the other is 2.17.

I can swap plates from being the orifice to the test piece. I cannot take my test pressure to 25" without going well over 100" flow in either configuration.

Am I missing something here? I think it is something that I am doing wrong.

The 1.96 plate was calibrated at 251 @25" and the 2.17 is something that I made.

[bruce]

The way I figure it your 1.96 plate should show around 80% on your incline when tested against your 2.17 this is assuming a .60 Cd at 25".

I say "around" since I do not know the accuracy of the 2.17" orifice.

[larrycavan]

I guess I don't understand your calibration procedure well enough. In any case, it sounds like you're doing it differently than I would. That's not to say you're wrong...I just don't grasp what you're after with the way you're going about it.

To calibrate, you select a range of [for now] and assumed value.

You select a calibration plate of a known value at a known test pressure.

You flow that cal plate at that pressure using the orifice of assumed value and determine from those numbers what your orifice in the bench actually flows.

It's a comparison of a known to an unknown...

Larry

[SuperRunner]

Larry, I would assume that the 1.9 would be a smaller percentage than the 2.17, but that is not what is happening. Right now I would have to use a 2.5" orifice to get the 1.96 to show less than 100% @ 25". Does that seem right, or maybe it is my scale. I have a 9" verticle drop on the included manometer. I guess if I had a 12" verticle drop it might not read past 100%?


Does the size of your orifice have a direct impact on the verticle drop of the inclinded scale?

What are the pros and cons about going with a 12" drop vs a 9" drop?

I am still trying to grasp the math behind this, I think that is my problem.

[SuperRunner]

[bruce]

Setup your inclined so you show 80% when you flow the 1.96 against the 2.17 this should give you a good starting point. Make up some other orifice sizes at different percents and see if it holds out. I'm assuming your inclined scale is marked in percent of flow? You did use the inclined manometer spreadsheet downloadable on the forum to setup your scale?

[larrycavan]

Increases in Verticle Drop will extend the range capacity. You're giving yourself more measurable flow by increasing the Verticle drop.

Whatever your verticle drop is, that's your max measurable pressure drop. After that, you run out of scale. Pressure Drop is what you're measuring. Pressure differential from top to bottom side of the orifice inside the bench.

You can measure it with a U tube but it's harder to read small changes. The inclined functions exactly like a U tube, it just has the scale arranged in % arrangement. It reads % of the verticel pressure drop. Nothing more, nothing less.

For a 2.17" diameter orifice with a Cd of .62 and a 9" verticle drop on your inclined manometer using 1.0SG fluid [or your scale being compensated for some other weight fluid] you would have a measurable flow of 191.55 CFM flow range.

For the same orifice but a 12" drop it would be 228.18 CFM.

Now, the tricky part is...Does the orifice have an actual .62 Cd?

You're proving that by comparing it with a calibration orifice of a known flow value at a known test pressure.

Without the known calibration to compare the orifice to, you are going to drive yourself crazy.

You first have to know the construction of your manometer in order to rely on what it reads. There are 4 basic adjustments to the inclined manometer that can influence the readings.

1. fluid sg
2. verticle rise
3. inclined leg to well ratio
4. a properly laid out scale

If all 4 of those pieces of criteria are not correct or compensation in one because of a change in another has not been taken into account, you will get bogus readings.

Larry

[larrycavan]

If I recall correctly, I noticed on someone's bench photos recently that the U tube manometer was not marked out in the usual fashion of .5" = 1"....if that was your bench and if you haven't accounted for that, it could be throwing you off.

When looking at one leg of a U Tube verticle manometer with 1.0 SG fluid, for every .5" of actual travel, you can call it 1". That way you don't have to measure both sides of the U tube. If you don't and you are looking for 10" of pressure, you'll be at 20"......hope that makes sense...

Larry

[SuperRunner]

[larrycavan]

Do you mean a SF300. That uses a Dwyer 246. That guage is for 6" of rise and uses .826 fluid. The scale should be 20". Is that the length of the scale?

If it is 20" then using the spreadsheet things work out like this.

20" scale
.826 fluid
.125 inclined leg tubing
.5 fluid well
17.45 degreee Scale Angle
5.99 Water Column max


If you need to raise the manometer to 60 degrees then I feel there's something going on.

I agree with Bruce's estimate on the flow rating of about 80% using the 2.17 and 1.96 plates with a 25" test pressure.

[SuperRunner]

Could it be that my tube id is 1/8 and my resivoir is 1.36 ID, although I don't think so.

Also, I used the spreadsheet to, but were to you get the verticle of 5.99 with a 17 degree incline. I don't get those numbers when I put in the numbers.