Basic Documentation
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Valve Reference
2-way Flow Coefcients (Cvs)
Size
Degrees Open
10° 20° 30° 40° 50° 60° 70° 80° 90°
2" 0 1.3 5 14 26 40 52 59 60
2-1/2" 0 1.4 6 21 44 74 107 138 151
3" 0.7 1.5 8 29 67 115 175 234 262
4" 1.7 15 48 107 196 318 463 589 647
5" 3 32 99 206 362 579 832 1045 1141
6" 4 47 145 295 510 810 1160 1450 1580
8" 6 84 239 450 751 1190 1754 2385 2892
10" 9 133 360 652 1064 1683 2524 3596 4593
12" 12 192 509 899 1449 2288 3470 5085 6682
14" 75 340 770 1400 2200 3400 5600 7900 10000
16" 100 440 1000 1800 2800 4500 7400 10800 13000
18" 130 570 1300 2300 3600 5800 9600 15000 18000
20" 150 710 1600 2900 4600 7200 12000 18400 22000
Table Note:
Flow Coefcients (Cv) = The amount of water in gallons per minute, at 60°F that will pass through a given orice with a one pound pressure drop.
2-way and 3-way Proportional Control Valves
Control Valves are the most important element of a uid handling
system and proper selection of these valves is crucial for efcient
operation of the process. When sizing buttery valves for control,
it is imperative to have certain requirements of the system.
You must have:
• Maximum ow requirement: This would be equivalent to the
design ow and provided or converted to gallons per minute.
• Maximum pressure drop allowed: The Consulting Engineer
usually provides this factor and are typically 3 to 5 psi max.
However, the pressure drop should never exceed one half of
the inlet pressure.
Without these two factors, selection of a control valve would be
simply a guess.
Introduction
When selecting a buttery valve for water applications you must
rst determine the requirements of the valve assembly. The
rst question to ask is, “Will the valve be used for “Isolation” or
“Proportional Control” of the uid?” and “Does the application
require a 2-way or 3-way assembly?”
2-way and 3-way Isolation Valves
When selecting a valve for isolation purposes, it is seldom necessary
to calculate ow requirements beyond the published Cvs (ow
coefcients)* of the valve. These valves are typically line size and
require the lowest pressure drop available in the full open position.
It may be possible to supply a valve smaller than the actual line size
and still obtain a low-pressure drop. However, the cost of reducing
anges will typically offset any savings incurred by reducing the
valve size. The 2- and 3-way Flow Coefcient charts, below and on
I-16, provide Cv values for Siemens buttery valves.
Buttery Valve Selection and Sizing