PRESSURE DROP

Flow coefficient Kv anc Cv

The fl ow coeffi cient Kv is the fl ow in m3/h of water at an average temperature of 20 °C, crossing the valve while creating a headloss of 1 bar.

The relation between Cv and Kv coefficients is : Cv = 7/ 6 Kv

Simplified formula

Kv : Flow coefficient of the valve
Q : Flow in m3/h
Δp : Pressure drop in the valve in bar
p1 : Absolute upstream pressure in bar
p2 : Absolue downstream pressure in bar
QN : Flow in normal conditions (0 °C, 76 mm Hg) en m3/h
T : Absolute temperature of the fluid in °k
φp1 : Volumic weight of the fluid in kg/cm3
φN : Volumic weight in normal conditions in kg/cm3

PRESSURE

• Ø 1/2" - 3/4" : PN 25
• Ø 1" - 4" : PN 16
• Ø 5" - 8" : PN 10

TEMPERATURES

From -20°C to 150°C according to the diaphragm

VACUUM SERVICE

Fives grades of vacuum may be given

• rough vacuum : suitable for use down to 1 Torr
• primary vacuum : from 1 to 10-3 Torr
• secondary vacuum : from 10-3 to 10-6 Torr
• high vacuum : from 10-6 to 10-8 Torr
• ultravacuum : higher than 10-8 Torr

Pressure units

1 Pa = 0,01 mbar = 0,0075 Torr
1 Torr = 1 mm de Hg = 1,3332 mbar = 133,32 Pa

Others units

1 mbar.1/s = 1 atm.cm3/s = 0,76 Torr.1/s = 760 lusec
1 lusec = 1,3.10-3 mbar.1/s = 10-3 Torr.1/s.

Leakage rate

The notion of leakage gas flow is used. The leakage gas flow is 1 mbar.1/s when a closed tank of 1 liter under vaccum increases of 1 mbar into 1 s.

Use of diaphragm valves

The diaphragm valves are particularly suitable for vaccum applications.
A standard valve may be used for rough and primary vaccum. For secondary vaccum, a machined body and low permeability diaphragms as butyl and viton are recommended.

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