Solenoid valves - Bürkert Fluid Control Systems

3.2.2. k v value
The k v value, which is defined as follows,
has been introduced to describe
the flow behavior of valves:
■ The k v value is the volume flow
·
V (in m 3 /h) of water ( 0 =1kg/dm 3 )
at a temperature between 5 and 40
°C at a pressure drop (permanent
pressure loss) at the valve of
0 =100 kPa.
Since the k v value designates a volume
flow (m 3 /h), the frequently encountered
designations “flow-rate coefficient” or
“valve coefficient” are misleading since
they presuppose that k v is non-dimensional.
3.2.3. c v value and Q Nn value
In countries using the Imperial system,
the cv value is used as the flow parameter
instead of the k v value.
From this equation, we can then deduce
the following for the k v value:
k v = · A
2 · p 0
0
Equation 3
For a valve, the k v value can be determined
experimentally on the basis of
the assumptions contained in the definition
( 0 und 0 ). It thus represents
a parameter for characterizing a valve.
Thus, the k v value can initially be used
as a measure of the quality of the flowdynamics
design of valves. If, for example,
we compare several valves
with the same nominal diameter, the
valve with the highest k v value is the
best-designed valve from a flow dynamics
perspective.
■ The c v value is the volume flow (in
US gallons/minute) of water at a
temperature of 60 °F with a pressure
loss of 1 psi through the valve.
Where:
1USgallon/minute = 0.227 m 3 /h and
1 psi = 0.069 bar (psi: pounds per
square inch).
The QNn value, which is defined as
follows, is another flow parameter used
for valves in pneumatics. The Q Nn value
is the volume flow (in liters/minute) of
air at a temperature of +20 °C and at
an input pressure of 6 bar and a pressure
drop through the valve of 1 bar.
The following conversion factors apply
for converting k v to c v and Q Nn :
k v = 0.86 c v
k v = 1078 Q Nn .
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