Woodward 3171A, Руководство по эксплуатации продукта, Страница: 29 / 47

Manual 26731 EM35MR1/3171A Gas Valve
Woodward 19
Chapter 6.
Valve Sizing—Non-DLE Applications
Determination of Effective Area
In order to choose the proper size of valve for an application, the
effective area
required to meet your maximum flow requirement must first be determined. The
effective area is determined using the following equations.
Where:

P1 = Valve inlet pressure (psia)

P2 = Valve discharge pressure (psia)

K = Ratio of specific heats for the gas
(1.300 typical for standard natural gas at 60 °F)

Sg = Specific gravity relative to air for the gas
(0.60 typical for standard natural gas)

Flow = Valve metered flow (lb/h)

T = Temperature of the gas (Deg Rankine)
(Deg R = Deg F + 459.7)

Z = Gas Compressibility Factor
(essentially 1 for most applications—see the following graph)
The valve size selected should be sized to be adequate for worst-
case flow conditions. This would be minimum P1, maximum P2,
maximum flow, and maximum temperature.
R7( ) K
2
1 K
K
K 1
If
P2
P1
R7 Effective_Area
FLOW
. .
3955.289 P1
.
.
K Sg
. .
( ) K 1 T Z
P2
P1
2
K
P2
P1
1 K
K
If
<
P2
P1
R7 Effective_Area
FLOW
. .
3955.289 P1
.
.
K Sg
. .
( ) K 1 T Z
R7
2
K
R7
1 K
K