41
Start-up
Type 3280, 3285
The flow characteristic k
V
= f(s) indicates the flow-rate of a valve, expressed by the k
V
value depending on the
position/angle s. It is specified by the design of the valve seat and the seat seal. In general two types of flow char-
acteristics are implemented, the linear and the equal percentage.
In the case of linear characteristics identical k
V
value changes k
V
are assigned to identical stroke changes ds
(dk
v
=n
lin
*ds). In the case of an equal percentage characteristic an equal percentage change of the k
V
value cor-
responds to a stroke change ds (dk
v
/k
v
=n
eqlprct
*ds). The operating characteristic Q = f(s) states the correlation
between the volume flow Q, which flows through the valve installed in the system, and the position/angle s.
In the case of control tasks for closed-loop control systems it is usually particular demands which are placed on
the course of the operating characteristic, e.g. linearity. For this reason it is occasionally necessary to correct the
course of the operating characteristic in a suitable way. Equal percentage characteristics 1:25, 1:33, 1:50, 25:1,
33:1 and 50:1 and a linear characteristic can be set. Furthermore, a characteristic can be freely programmed.
Position set-point value [%]
CMD
Standardised valve stroke [%] (POS)
Figure 24: Characteristics
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