CEMP-E
TI 810-11
30 November 1998
Table 2-3. Available control valves with Kv (Cv) in the range of 14 to 22 (16 to 25)
3
Valve Type
Valve Size
Kv (m /hr @ ∆p = 100 kPa) /
Cv (gpm @ ∆p = 1 psi)
Normally-open water valve
25 mm (1-inch)
15.5 / 18
Normally-open water valve
32 mm (1-1/4 inch)
19.2 / 22.2
Normally-open water valve
32 mm (1-1/4 inch)
14.7 / 17
Normally-open water valve
32 mm (1-1/4 inch)
13.8 / 16
Normally-open water valve
40 mm (1-1/2 inch)
21.6 / 25
Normally-open water valve
40 mm (1-1/2 inch)
17.3 / 20
Three-way valve
25 mm (1-inch)
15.5 / 18
Three-way valve
25 mm (1-inch)
15.6 / 18.1
Three-way valve
32 mm (1-1/4 inch)
13.8 / 16
Three-way valve
32 mm (1-1/4 inch)
14.7 / 17
Three-way valve
40 mm (1-1/2 inch)
21.6 / 25
Three-way valve
40 mm (1-1/2 inch)
18.2 / 21
At this point, the designer will check the line size of the piping circuit and check the piping size of the
reducing fittings. A good choice for the designer would be to show the Kv at 14 (Cv at 16) and the maximum
close-off pressure at 140 kPa (20 psig) in this example because there are more control valves available in
the range of 14 to 17.5 (16 to 20) (a plus 25 percent deviation) than there are in the range of 17.5 to 21.25
(20 to 25) (a plus 25 percent deviation).
c. The Kv (Cv) calculations for selecting a butterfly valve are identical to those for any valve except that
the valve Kv (Cv) is selected using the calculated Kv (Cv) at a maximum of 70 degrees open when the valve
is to be used in a modulating control application. (The butterfly valve does not have a good modulating
control characteristic curve between 70 degrees and 90 degrees open.)
d. When selecting control valves for liquid service other than water, the designer will take into account
the specific gravity of the liquid. If the liquid has a specific gravity of 1.05, for the same flow rate, the liquid
flow will produce a 5 percent greater pressure drop through the valve.
14. CALCULATION OF STEAM CONTROL VALVE FLOW COEFFICIENT (Kv / Cv).
a. Calculating and selecting the required Kv (Cv) of a steam valve
requires the designer to consider:
(1) The saturated or superheated condition of the steam.
(2) The inlet pressure at the valve.
(3) The minimum required steam pressure entering the steam-condensing apparatus at peak
heating load.
2-24
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