Burkert 8626 Instructions De Service page 15

In this case, in analogy to equations (1) and (2), one first determines from the
desired nominal flow rate Q
coefficient of the overall system k
2
2
⎛ ⎞
⎛ ⎞
1 1
⎜ ⎟
⎜ ⎜ ⎟ ⎟
= +
⎜ ⎟
k k
⎝ ⎠
⎝ ⎠
Vges Vs
which describes series connection of the resistances of the MFC (k
system (k ), one can determine, with known k
Va
MFC or the nominal diameter of the servo element. This will be greater than if the
other flow resistances were not present.
The so-called valve authority
( )
∆
p k
ψ
= =
V 0 [ Vs
( )
∆ 2
p
+
k
0
Va
is important for the control characteristics of the MFC in the system. It should not
be less than 0.3 ... 0.5.
Meaning of the symbols in the equations:
k flow coefficient of the system with MFC installed
Vges
k flow coefficient of the system with MFC not installed (to be determined by
Va
"short-circuiting" the piping at the point of installation)
k flow coefficient of the MFC with fully opened servo element in [m³/h]
Vs
ρ
density of the medium in [kg/m
N
273 K)
T temperature of the gas in K
1
p , p absolute pressures in [bar] before and after the MFC
1 2
∆p = p
- p
1 2
Q maximum flow rate of the valve in [l
max
Q maximum flow rate of the MFC in [l
nenn
the setpoint has been made
(∆p) pressure drop over the entire system
0
(∆p) fraction of the pressure drop occurring over the MFC with the valve fully
V0
open
and the pressures p
nom
. Via the relationship
Vges
2
⎛ ⎞
1
⎜ ⎜ ⎟ ⎟
k
⎝ ⎠
Va
Va
2
]
2
k
Vs
3
] under standard conditions (1013 mbar,
/min]
N
/min] when correction to 100 % of
N
* *
and p , the minimum flow
1 2
(3)
) and the
Vs
, the required k value of the
Vs
(4)
MFC/MFM - 15