Weco
Butterfly Valve Home
Weco Butterfly Valves
Sizing Information
NonCompressible Fluids
Use the following equations for sizing valves handling liquids
Where: 

= 
Flow in gallons per minute (gpm) 

= 
Pressure Drop (psi) 

= 
Inlet pressure (psia) 

= 
Outlet Pressure (psia) 

= 
Specific Gravity of Liquid (Water = 1.0) 

= 
Valve Coefficient (Refer to Appropriate Table) 
The equations listed above are the basis for the WECO sizing
nomogram. The nomogram is a method of solving the equations above quickly
and simply when the service fluid is water.
Example 

Given:

A 6" Weco Butterfly Valve is to be installed in a line handling
500 gpm of water. 
Find: 
Maximum pressure drop across the valve when in the full open and
60° open positions 
Solution: 
This problem may be solved using the nomogram or equation (C) 
First Using the Nomogram: 
Enter nomogram on right side for a flow rate of 500 gpm. Draw
horizontal line until it intersects the 6" valve line. From this
point draw a vertical line until it intersects the 90° open line.
Project line horizontally to the left and read
.061 psi for 60° open. 
Using Equation C 
Pressure Drop =

Where: 

= 
500 gpm 

= 


= 
Specific Gravity of Liquid (Water = 1.0) 

= 
2020 @ 90° open (from tables) 
GPM @ PSI @ Various Disc
Angles 
Valve Size, In

10° 
20° 
30° 
40° 
50° 
60° 
70° 
80° 
90° 
2 
1.59 
6.17 
14.2 
26.3 
44.5 
70.6 
105 
135 
159 
2^{1/}_{2} 
2.33 
9.06 
20.9 
38.6 
65.3 
104 
156 
215 
266 
3 
3.50 
13.6 
31.4 
57.9 
98.0 
156 
240 
342 
457 
4 
6.16 
23.9 
55.1 
102 
173 
274 
423 
625 
860 
5 
9.56 
37.2 
85.6 
158 
268 
426 
656 
970 
1,320 
6 
13.7 
53.3 
123 
227 
384 
610 
941 
1,420 
2,020 
8 
24.2 
94.3 
217 
401 
679 
1,080 
1,66 
2,500 
3,540 
10 
37.3 
145 
334 
617 
1,040 
1,660 
2,560 
3,830 
5,580 
12 
53.7 
209 
481 
888 
1,500 
2,390 
3,690 
5,620 
8,080 
14 
61 
166 
650 
1,300 
2,100 
3,500 
5,220 
8,000 
13,000 
16 
81 
477 
960 
1,700 
2,900 
4,920 
7,000 
11,000 
17,000 
18 
125 
535 
1,120 
1,960 
3,500 
5,800 
8,000 
15,000 
19,000 
20 
161 
723 
1,500 
2,700 
4,800 
7,900 
12,500 
18,500 
27,000 
24 
305 
921 
2,000 
3,640 
6,175 
10,350 
17,500 
24,000 
35,000 
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