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Diaphragm Valve Sizing |
Flow computations
Since rate of flow depends upon the pressure drop through the valve,
the CV values are given at vaious stages of the opening.
The CV is the valve coefficient of the flow and represents the flow of
water through the valve in gpm with a 1 psig pressure drop. To calculate
flow with the CV table, use 100% opening for ON-OFF service and 50%
opening for THROTTLING service.
LIQUID FLOW FORMULA
At pressure drops of other than 1 psig
Q = CV(P/G)1/2
Where:
Q = actual flow (gpm)
P = actual pressure drop (psig)
G = specific gravity
Cv = flow factor from table
GAS FLOW FORMULA
|
Q = 1360 CV(P/GT)1/2 |
[ |
P1 + P2
|
]1/2
|
| 2 |
Where:
Q = volumetric flow (scfh)
G = specific gravity of gas (air at 0 psig and 60°F is 1.0)
T = absolute temperature of flowing medium (°F + 460)
P1 = inlet pressure (saia)
P2 = outlet pressure (psia)
P = (P1 - P2) pressure drop (psia)
CV = flow factor from table
Liquid velocity
Liquid velocity is a very important design consideration. In order to assure
maximum life of liner and diaphgram, it is recommended that velocity be kept
to a maximum of 10 feet per second over the weir. When handling abrasive
liquids, special considerations are necessary. Consult you Resistoflex
representative.
LIQUID VELOCITY FORMULA
V = .321 (Q/A)
Where:
V = velocity (ft/s)
Q = flow (gpm)
A = Area over wier from table
| Valve coefficient of flow |
Valve size1
inches |
CV flow factors
%
valve opening |
| 25% |
50% |
75% |
100% |
| 1 |
5.9 |
7.1 |
7.1 |
7.2 |
| 1 1/2 |
15.0 |
21.8 |
23.2 |
24.4 |
| 2 |
34.3 |
46.3 |
46.5 |
46.7 |
| 2 1/22 |
--- |
--- |
--- |
68.0 |
| 3 |
58.0 |
93.0 |
101.0 |
107.0 |
| 4 |
115.0 |
117.0 |
213.0 |
233.0 |
| 6 |
252.0 |
334.0 |
378.0 |
403.0 |
| 8 |
675.0 |
1035.0 |
1062.5 |
1082.5 |
1The 1, 1 1/2, 2, 3, 4, 6, and 8-inch sizes were
tested by an independent testing laboratory in accordance with Fluid Controls Institute,
Inc., "Recommended Voluntary Standards for Measurement Procedures for Determining
Control Valve Flow Capacity."
2The CV for the 2 1/2-inch size was calculated by an area
relationship assuming constant velocity.
| Area over the wier
Dimensions: square inches |
| Valve Size inches |
% Open |
| 10 |
20 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
100 |
| 1 |
.10 |
.18 |
.25 |
.32 |
.39 |
.45 |
.51 |
.56 |
.61 |
.64 |
| 1 1/2 |
.23 |
.42 |
.61 |
.80 |
.96 |
1.10 |
1.25 |
1.38 |
1.50 |
1.58 |
| 2 |
.40 |
.72 |
1.06 |
1.32 |
1.63 |
1.88 |
2.10 |
2.32 |
2.52 |
2.66 |
| 2 1/2 |
.56 |
1.06 |
1.53 |
1.96 |
2.36 |
2.74 |
3.08 |
3.40 |
3.63 |
3.88 |
| 3 |
.86 |
1.62 |
2.32 |
2.95 |
3.56 |
4.18 |
4.66 |
5.12 |
5.58 |
5.90 |
| 4 |
1.40 |
2.66 |
3.78 |
4.84 |
5.80 |
6.80 |
7.62 |
8.40 |
9.09 |
9.60 |
| 6 |
3.20 |
5.90 |
8.20 |
10.50 |
12.60 |
14.62 |
16.41 |
18.25 |
19.72 |
21.00 |
| 8 |
5.92 |
11.41 |
16.25 |
20.62 |
25.00 |
29.00 |
32.80 |
36.00 |
38.80 |
41.00 |
"This page is a machine translation of the source page, which is written in
English. This translation is intended to provide a general idea of the
page's content, and is not guaranteed for accuracy."
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