5-6
EB 8359-2 EN
Installation
Risk of malfunction due to failure to comply
with air quality requirements.
Î
Only use supply air that is dry and free
of oil and dust.
Î
Read the maintenance instructions for
upstream pressure reducing stations.
Î
Blow through all air pipes and hoses
thoroughly before connecting them.
5.4.1 Pressure gauges
To monitor the positioner, we recommend in-
stalling pressure gauges for the supply air
and signal pressure (see accessories in sec-
tion
5.4.2 Supply pressure
The required supply air pressure depends on
the bench range and the actuator's direction
of action (fail-safe action).
The bench range is written on the nameplate
either as the bench range or signal pressure
range. The operating direction is marked
FA
or
FE
or by a symbol.
Actuator stem extends (FA)
Fail-close
(for globe and angle valves)
Required supply pressure =
Upper bench range value + 0.2 bar,
minimum 1.4 bar
Actuator stem retracts (FE)
Fail-open
(for globe and angle valves)
For tight-closing valves, the maximum signal
pressure pst
max
is roughly estimated as fol-
lows:
pst
max
= F +
d² · π · ∆p
[bar]
4 · A
d
= Seat diameter [cm]
∆p
= Differential pressure across the valve
[bar]
A
=
Actuator area [cm²]
F
= Upper bench range value [bar]
If there are no specifications, calculate as
follows:
Required supply pressure =
Upper bench range value + 1 bar
The positioner output pressure is routed to
the top or bottom diaphragm case of the ac-
tuator as shown in
.
5.5
Selecting the range spring
The attached lever and the installed range
spring of the positioner are assigned to the
values of rated valve travel and the set point
as in Table 5-1.
In normal operation, the set point span is
100 % = 16 mA. A smaller span of, for ex
-
ample 50 % = 8 mA is only required for
split-range operation (
, right).
The span can be changed by exchanging the
range spring. On making adjustments to the
positioner, the travel must be adapted to the
set point and vice versa.
NOTICE
!
Table 5-1:
Range springs
Rated travel
[mm]
Min./max. travel [mm]
Set point (input signal)
Range spring
Standard travels for SAMSON valves with lever l (40 to 127 mm in length)
15
7.5 to 15
100 %
50 %
1
2
30
14 to 32
100 %
50 %
2
3
60
30 to 70
100 %
3
Further travel ranges with lever l and lever extension (40 to 200 mm in length)
20
7.5 to 26
100 %
50 %
1
2
40
14 to 50
100 %
50 %
2
3
> 60
30 to 90
100 %
3
100%
0%
4
20mA
Set point (input
signal)
Open
Travel
Closed
100%
0%
4
12
20mA
Dead band
Valve 2
Valve 1
Open
Travel
Closed
Normal operation
Split-range operation, two valves operating in
opposing directions
Fig. 5-8:
Normal or split-range operation
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