Control valves

Pressure reducing/surplussing valves

4.6.39

Sizing and selection

The required Kv can be calculated from the following formulae,

Where:

= Steam mass flow (kg/h)

= Liquid volume flow (m

3

/h)

= Gas flow at standard conditions: 0°C @ 1.013 bar a (m3/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 Kv from one of the adjacent

formulae. Select a valve whose Kv 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.

Critical pressure drop: P

2

£ 0.58 P

1

K

V

Non-critical pressure drop: P

2

P

1

Steam

Gas

Liquid

Recommended fluid velocities

 0.58 P

1

K

V

1

P

K

V

2

P

1

P

2

P

1

P

2

K

V

Steam

Gas

Liquids

P

1

P

2

Saturated

up to 2 bar g

10 to 40 m / s

2 to 10 m/s

Superheated

above 2 bar g

15 to 60 m / s

5 to 40 m/s

1 to 5 m/s

Page 4 of 5

TI-P186-01 CH Issue 10

SRV461S and SRV463S Stainless Steel Direct Acting Pressure Reducing Valves