Bronkhorst EX-FLOW Mass Flow Bedienungsanleitung PDF herunterladen (Seite 12)

BRONKHORST HIGH-TECH B.V.

1.6.2 Kv-value calculation

This calculation method can be used to determine the K

-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:

p p

⋅

∆

514

undercritical

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

⋅

257

overcritical

Units:

Flow :

m h

(gasflow)

Supply pressure :

in bara

Downstream press. :

in bara

Pressure difference :

∆p

= (

p p

1 2

−

) in bar

Temperature : T in Kelvin

Density :

n n

inkg m/ 3

The orifice diameter can be determined by: d= 7.6

[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]

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

3,6

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

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