Basic Documentation

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Example
The line size is 6" and the required ow is 600 GPM with a
maximum pressure drop of 5 psi. The square root of 5 is equal to
2.236. When divided into 600, the required Cv for this application
is: 268.336.
2. Select your valve size: Using the Flow Coefcients (Cvs), select
the appropriate valve size. If your required Cv is in between
valve sizes, choose the larger size valve. When selecting a 3–way
assembly, the Cv of the run should be selected.
Example
The line size is 6" and the calculated required Cv is 268.336.
The valve selected is a 4" with a rated Cv of 647.
Buttery valves are high capacity valves and require very little
pressure drop to control ow, which allows for reduction from the
line size when sizing valves. This pipe reduction affects the ow
characteristics and will reduce the effective Cv of the valve. This
phenomenon is known as the piping geometry factor (Fp), which
brings us to the nal step in valves sizing.
3- way Flow Coefcients (Cvs)
Degrees Open
0° 10° 20° 30° 40° 50° 60° 70° 80° 90°
90° 80° 70° 60° 50° 40° 30° 20° 10° 0°
2" 54 53 49 43 38 40 44 52 57 58
2-1/2" 114 108 93 74 52 64 78 102 126 135
3" 188 178 148 114 55 95 120 165 210 229
4" 385 374 348 313 150 295 345 419 482 511
5" 642 627 600 563 270 549 630 740 829 870
6" 935 909 867 809 483 780 895 1051 1180 1242
8" 1688 1573 1424 1271 796 1175 1367 1661 1994 2254
10" 2667 2430 2132 1856 1142 1685 1971 2439 3046 3570
12" 3938 3531 3019 2579 1629 2312 2715 3401 4368 5240
14" 5109 4825 4416 3719 2433 3514 3992 5259 6342 7173
16" 6735 6462 5832 4904 3213 4498 5265 6943 8567 9410
18" 9060 8724 7650 6372 4433 5778 6815 9056 11695 12785
20" 11229 10799 9545 7901 5619 7339 8449 11309 14423 15770
Table Notes:
Three-way valve assemblies Cvs are corrected from published two-way Cvs to account for line losses generated by the tee, and are calculated values only.
The pipe friction losses are a function of uid velocity through the pipe and the three-way Cvs listed are apparent for full ow through the pipe. Operation at
less than full capacity (lower velocity) will increase the actual Cvs
Buttery Valve Selection and Sizing
Sizing Example
With this information and assuming the media is water or a similar
media (glycol/water mix), a control valve can be properly sized for
the application by following these steps:
1. Calculate the required Cv: Using the following formula and
the information required above, you could calculate the ow
coefcient (Cv) of the control valve.
Whereas: GPM = The maximum ow requirement
P = The max. pressure drop (5 psi)
Cv=
GPM
∆ P