44
Sizing and selection The required K v can be calculated from the following formulae. Where: = Steam mass flow (kg/h) Control systems Pressure reducing/surplussing valves
= Liquid volume flow (m 3 /h)
= Gas flow at standard conditions: 0 °C @ 1.013 bar a (m ³ /h)
= Upstream pressure (bar absolute)
= Downstream pressure (bar absolute)
P 1 - P 2
=
(pressure drop factor)
P 1 = Specific gravity
= Absolute average gas temperature (Kelvin = °C + 273)
Selecting valve type and nominal diameter Using the required maximum flowrate and smallest differential pressure P 1 - P 2 , calculate the required K v from one of the adjacent formulae. Select a valve whose K v value is 30% greater than the calculated K v . The optimum working range of the selected valve should ideally be within the range of 10 to 70% of its K v . You should also note the reduction ratio (inlet pressure P 1 divided by outlet pressure P 2 ). If this exceeds the quoted pressure reduction ratio for the valve being considered the valve will not close.
4.6 62
Critical pressure drop: P 2
£ 0.58 P 1
K V
P 1
Steam
Non-critical pressure drop: P 2
0.58 P 1
K V
P
2
1
K V
Gas
P 1
P 1 P 2
P 2
K V
Liquid
P 1 P 2
Steam
Saturated
Superheated
10 to 40 m/s
15 to 60 m/s
Recommended fluid velocities
Gas
up to 2 bar g
above 2 bar g
2 to 10 m/s
5 to 40 m/s
Liquids
1 to 5 m/s
TI-P186-01 CTLS Issue 13
Page 6 of 7
SRV461S and SRV463S, SRV461S Food+ and SRV463S Food+ Stainless Steel Direct Acting Pressure Reducing Valves
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