Type 3285

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6.3. Flow characteristic

Determination of the K

V value

Note:

Once the K

V-value required for the application has been calculated, it can be compared with the KVS-values from the ordering chart. The

K

VS-value must be higher than the KV-value of the application, but should be neither too high nor too close to it - as a recommendation:

10 % higher.

Pressure drop

K

V value for liquids

K

V value for gases

[m3/h]

[m3/h]

Sub-critical

p2 > 2

p1

= Q

ρ

Δp

1000

= Q

514

QN

ρN

T

1

Δp

p2

Supercritical

p2 < 2

p1

= Q

ρ

Δp

1000

= Q

QN

ρN

T

1

257 p1

K

V

Flow coefficient

[m3/h] 1.)

Q

N

Standard flow rate

[m

N

3

/h] 2.)

p

1

Inlet pressure

[bar] 3.)

p

2

Outlet pressure

[bar] 3.)

∆p Differential pressure p

1…p2

[bar]

ρ

Density

[kg/m3]

ρ

N

Standard density

[kg/m3]

T

1

Medium temperature

[(273+t)K]

1.) Measured for water, ∆p = 1 bar

2.) At reference conditions 1.013 bar and 0 °C (273 K)

3.) Absolute pressure

Exemplary characteristic curve of the motor valve

Note:

The design of the seat size is very important for the proper functioning of electromotive proportional valves within the application. The seat

size must be selected in such a way that, on the one hand, the desired flow range is achieved and, on the other hand, when the valve is

fully open, a sufficient part of the total pressure drop takes place via the valve.

Reference value: Δp valve > 25 % of the total pressure drop

Otherwise, an ideal, linear valve characteristic is deformed into a curved system characteristic.

100

90

80

70

60

50

40

30

20

10

0

0

10

20

30

40

50

60

70

80

90 100

Stroke [%]

Linear flow characteristic - the K

VS values of the respective seat sizes can be found in chapter “6.2. Pressure range” on page 10.