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Bronkhorst EX-FLOW Mass Flow User Manual

Page 12

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BRONKHORST HIGH-TECH B.V.


1.6.2 Kv-value calculation

This calculation method can be used to determine the K

v

-value of the main orifice of a control valve.

Determine desired ∆p across valve.

p must be at least 20% of supply pressure, or in closed loop systems, of total pressure difference in loop. If

p is 20-50% of supply pressure, use formula:

K

T

p p

v

n

=

Φ

vn

514

ρ

2

undercritical

If ∆P is 50-100% of supply pressure, use formula:

K

p

T

v

vn

n

=

Φ

257

1

ρ

overcritical

Units:

Flow

:

Φ

vn

in

m h

n

3

(gasflow)

Supply pressure

: p

1

in bara

Downstream press.

: p

2

in bara

Pressure difference

:

p

= ( p

p

1

2

) in bar

Temperature

: T in Kelvin

Density

:

ρ

n

n

inkg m

/

3


The orifice diameter can be determined by: d= 7.6 K

v

[mm]

1.6.3 Maximum pressure drop

For (pilot) solenoid operated control valves with small orifices the maximum allowable pressure drop for

gases is according to the table.

Diameter [mm]

K

v

Normally closed

p max. [bard]

Normally opened

p max. [bard]

0,05

0,07

0,10

0,14

0,20

0,30

0,37

0,50

0,70

1,00

1,30

1,50

1,70

2,00

4,33 x 10

-5

8,48 x 10

-5

1,73 x 10

-4

3,39 x 10

-4

6,93 x 10

-4

1,56 x 10

-3

2,37 x 10

-3

4,33 x 10

-3

8,48 x 10

-3

1,73 x 10

-2

2,93 x 10

-2

3,90 x 10

-2

5,00 x 10

-2

6,63 x 10

-2

40

30

30

30

30

30

30

30

24

12

8

6

5

3,6

30

20

20

20

20

20

20

20

15

8

5

n.a.

n.a.

n.a.

For pilot operated valves the maximum pressure drop is limited to 20 bard. If the the pressure drop during

start-up is higher, it is preferred to install a bypass valve. During start-up this valve should be opened. Also

the minimum pressure drop is limited. For exact figures consult factory or proceed according to the technical

data and/or additional instructions given by the sales office or department.

page 12

9.17.028