Burkert 8630 Instructions De Service page 155

A practical rule for the determination of the k
called 'valve authority Ψ :
( )
∆
p
Ψ = =
V 0
( )
∆
p
0
with
(∆p) : pressure drop with a fully open valve
V0
(∆p) : pressured drop over the complete installation
0
For valve authority Ψ Ψ Ψ Ψ Ψ < 0,3 the valve is oversized.
NOTE
In this case, the flow resistance with a fully open valve is much lower than the other components of the
installation. This means that only in the lower opening range, the valve position is working according to the
characteristics. For that reason the characteristics are strongly deviated. This can be partially compensated
and the characteristics linearized within the limits by using an equal percentage characteristic between set
position and the plug travel.The valve authority Ψ Ψ Ψ Ψ Ψ should, even when using a corrected characteristic, be
> 0,1.
The control behaviour (standard choice, maximum adjustment time) is strongly dependent on the working
point when using a corrected characteristic.
154
value for the upper limits in respect to continuous valves consists of using the so
VS
2
k
Va
+
2 2
k k
Va VS
(3)
Operating instructions no. 800607