Orifice vs calibration plate

[SuperRunner]

[SuperRunner]

Ok after some reading, I think I understand the math a little better, although I don't get the concept.

Anyway, lets say I go with a 6" verticle on the inclined, and the specific gravity is .826 and I want to run a test pressure at 28" this is what I need to do..
squareroot(6/28)*89 = 37.44

then if I want a 300cfm orifice, I need to...

300/37.44 = 8.0128 sq/in

So in the end, I would need a 3.194 hole to get 300cfm at 28"

Is this correct?

[larrycavan]

Here's the best way I can explain it. You're on the right track now. Keep It Simple.

Using 6" of water column as max measurable pressure and with the understanding that the inclined manometer is setup and scaled properly to read 0"-6" of water column.

That requires the proper adjustments to tubing, well and fluid sg [the spreadsheet is attached below]

Everything you calculate for orifice flow capacity is based on 6".

3.194 orifice diameter
6.000 water column [measured pressure drop]
0.62000 [orifice Cd [might vary]
8.0124 orifice area in square inches
338.83 CFM capacity at 6" pressure drop.

If the inclined manometer's configuration / accuracy is in question, it's easy enough to verify it by connecting the inclined manometer in parallel with the verticle [U Tube] and confirming the readings at 3 points. They should correspond.

25% - 50% - 100%

Those three points should correspond directly to the Dp (WC in) readings of 0.37 - 1.5 - 5.99

You would do that by connecting the inclined to the U Tube with T fittings. Both manometers will then be reading off the same pressure probes [top plenum and atmospheric pressure]


Tube I.D. 0.125
Reservoir I.D. 0.5
Scale Length 20.000
Scale Vetical Height 6.0
Fluid density 0.826
Scale Angle 17.45760312


Incline Manometer Scale
% of flow Ds (in) Dp (WC in)
1.0% 0.0020 0.00
2.0% 0.0080 0.00
3.0% 0.0180 0.01
4.0% 0.0320 0.01
5.0% 0.0500 0.01
6.0% 0.0720 0.02
7.0% 0.0980 0.03
8.0% 0.1280 0.04
9.0% 0.1620 0.05
10.0% 0.2000 0.06
11.0% 0.2420 0.07
12.0% 0.2880 0.09
13.0% 0.3380 0.10
14.0% 0.3920 0.12
15.0% 0.4500 0.13
16.0% 0.5120 0.15
17.0% 0.5780 0.17
18.0% 0.6480 0.19
19.0% 0.7220 0.22
20.0% 0.8000 0.24
21.0% 0.8820 0.26
22.0% 0.9680 0.29
23.0% 1.0580 0.32
24.0% 1.1520 0.34
25.0% 1.2500 0.37
26.0% 1.3520 0.40
27.0% 1.4580 0.44
28.0% 1.5680 0.47
29.0% 1.6820 0.50
30.0% 1.8000 0.54
31.0% 1.9220 0.58
32.0% 2.0480 0.61
33.0% 2.1780 0.65
34.0% 2.3120 0.69
35.0% 2.4500 0.73
36.0% 2.5920 0.78
37.0% 2.7380 0.82
38.0% 2.8880 0.86
39.0% 3.0420 0.91
40.0% 3.2000 0.96
41.0% 3.3620 1.01
42.0% 3.5280 1.06
43.0% 3.6980 1.11
44.0% 3.8720 1.16
45.0% 4.0500 1.21
46.0% 4.2320 1.27
47.0% 4.4180 1.32
48.0% 4.6080 1.38
49.0% 4.8020 1.44
50.0% 5.0000 1.50
51.0% 5.2020 1.56
52.0% 5.4080 1.62
53.0% 5.6180 1.68
54.0% 5.8320 1.75
55.0% 6.0500 1.81
56.0% 6.2720 1.88
57.0% 6.4980 1.95
58.0% 6.7280 2.01
59.0% 6.9620 2.08
60.0% 7.2000 2.16
60.5% 7.3205 2.19
61.0% 7.4420 2.23
61.5% 7.5645 2.27
62.0% 7.6880 2.30
62.5% 7.8125 2.34
63.0% 7.9380 2.38
63.5% 8.0645 2.41
64.0% 8.1920 2.45
64.5% 8.3205 2.49
65.0% 8.4500 2.53
65.5% 8.5805 2.57
66.0% 8.7120 2.61
66.5% 8.8445 2.65
67.0% 8.9780 2.69
67.5% 9.1125 2.73
68.0% 9.2480 2.77
68.5% 9.3845 2.81
69.0% 9.5220 2.85
69.5% 9.6605 2.89
70.0% 9.8000 2.93
70.5% 9.9405 2.98
71.0% 10.0820 3.02
71.5% 10.2245 3.06
72.0% 10.3680 3.10
72.5% 10.5125 3.15
73.0% 10.6580 3.19
73.5% 10.8045 3.24
74.0% 10.9520 3.28
74.5% 11.1005 3.32
75.0% 11.2500 3.37
75.5% 11.4005 3.41
76.0% 11.5520 3.46
76.5% 11.7045 3.50
77.0% 11.8580 3.55
77.5% 12.0125 3.60
78.0% 12.1680 3.64
78.5% 12.3245 3.69
79.0% 12.4820 3.74
79.5% 12.6405 3.78
80.0% 12.8000 3.83
80.5% 12.9605 3.88
81.0% 13.1220 3.93
81.5% 13.2845 3.98
82.0% 13.4480 4.03
82.5% 13.6125 4.08
83.0% 13.7780 4.13
83.5% 13.9445 4.18
84.0% 14.1120 4.23
84.5% 14.2805 4.28
85.0% 14.4500 4.33
85.5% 14.6205 4.38
86.0% 14.7920 4.43
86.5% 14.9645 4.48
87.0% 15.1380 4.53
87.5% 15.3125 4.58
88.0% 15.4880 4.64
88.5% 15.6645 4.69
89.0% 15.8420 4.74
89.5% 16.0205 4.80
90.0% 16.2000 4.85
90.5% 16.3805 4.90
91.0% 16.5620 4.96
91.5% 16.7445 5.01
92.0% 16.9280 5.07
92.5% 17.1125 5.12
93.0% 17.2980 5.18
93.5% 17.4845 5.24
94.0% 17.6720 5.29
94.5% 17.8605 5.35
95.0% 18.0500 5.40
95.5% 18.2405 5.46
96.0% 18.4320 5.52
96.5% 18.6245 5.58
97.0% 18.8180 5.63
97.5% 19.0125 5.69
98.0% 19.2080 5.75
98.5% 19.4045 5.81
99.0% 19.6020 5.87
99.5% 19.8005 5.93
100.0% 20.0000 5.99


You have to know, right from the beginning, that your scale is accurate.

Confirm that, then worry about calibrating.
Once you have established that your inclined manometer is properly setup, then the calibration process can begin.

You'll nail it down alright...the bench looks good. Pay attention to the details.....[been there..done that]

Larry C

[86rocco]

[SuperRunner]

I think I am actually starting to grasp the concept a little..I am sure after a bit, I actually be able to visualize it.

So, if I wanted to say, change my inclined 10 inches of verticle drop, my scale would no longer be accurate since it was made for 6 inches?

What are the advantages to using a small verticle drop with large orifice vs large verticle drop with smaller orifices? Does one give you a better overall testing capacity of the bench, or does that not really matter?

I want to be able to flow test intake manifolds, so I need to get the most out of my bench.

Oh, and thanks for your help, I really havn't even looked at the math until now, as I really needed to see it in action before I could understand.

[86rocco]

[larrycavan]

At this point, I suggest sticking to the basics. Verify your inclined manometer.

If you dont' know with 100% certainty that you can believe what it reads, you will guess at calibration till the sun burns out......

Larry

[SuperRunner]

[86rocco]

No, never change the gravitational constant, that number is related only to the size and mass of the earth, for the purposes of these calculations, put 0.826 in for the fluid density in the spreadsheet tab named "Inclined manometer compensation"

And using a denser fluid like water in your manometer won't mess up the scale, it'll just change the cfm value of 100%, Using a density fluid has the same effect as increasing the angle of the incline.

[SuperRunner]

ok, I think I am getting it.

For a 10" rise witha 1.2" ID reservoir, with water, the drop would actually be 10.2. With .826 SP the drop would then change to 8.44" instead.

Is this correct? If so, by golly, I think I've got it.

[86rocco]

By golly you DO have it!

Now, if you want to calculate the CFM value of 100% for a particular orifice with that manometer set-up, put 8.44 into Cell C7 of the "formula" sheet, that's the cell labelled "Pressure difference", then enter the particulars of your orifice and the CFM value for 100% will appear in the formula sheet cell C11 labelled FLOW

And if you want the spreadsheet to do that automatically, change the entry in cell C7 to "='Inclined Scale Compensation'!D149". Then any changes to the manometer set-up or the orifice set-up will automatically be reflected in cell C11.

[SuperRunner]

Man, you guys ROCK!!!! It works.

I just made a plate that flows 300cfm(by no means sharp edge though).

But anyway, I tested it against 2 different calibrated plates along with some venturi inserts and everything was DEAD ON...within .05%.

Although I think I may have some lower plenum and some leakage between the motor chambers as I could only get up to around 340 cfm @25". I should be able to do twice that...I would think. That seems like pretty excessive leakage.

[86rocco]

Math rocks when you get it right. Congrats!

[larrycavan]

Great! sounds like you nailed it down now. Rocco's spreadsheet for manometers makes life sooooo much easier when it comes to manometer setup. It's as "plug and play" as you're going to get...

Larry C