Samson 3725 series Mounting And Operating Instructions - Connections
5
Connections
5.1 Pneumatic connections
NOTICE
The threaded connections in the positioner
housing are not designed for the direct con-
nection of pneumatic fittings!
The screw fittings must be screwed into the
connecting plate, the pressure gauge mount-
ing block or the connection block from the
accessories.
The pneumatic connections are optionally
designed as a bore with ¼ NPT or G ¼
thread.
The customary fittings for metal and copper
pipes or plastic hoses can be used.
Keep the length of the line as short as possi-
ble to avoid delays in control signal trans-
mission.
Note: The supply air must be dry and free
from oil and dust.
The maintenance instructions for upstream
pressure reducing stations must be ob-
served.
Blow through all air pipes and hoses thor-
oughly prior to connecting them.
If the positioner is attached directly to the
Type 3277 Actuator, the connection of the
positioner's output pressure to the actuator is
fixed.
For attachment according to IEC 60534-6
(NAMUR), the signal pressure can be routed
to either the top or bottom diaphragm
chamber of the actuator, depending on the
actuator's fail-safe action "Actuator stem ex-
tends" or "Actuator stem retracts".
For rotary actuators, the manufacturer's
specifications for connection apply.
5.1.1 Signal pressure gauges
To monitor the supply air (Supply) and sig-
nal pressure (Output), we recommend
mounting pressure gauges (see accessories
in section 4.5).
5.1.2 Supply pressure
The required supply air pressure depends on
the bench range and the actuator's operat-
ing direction (fail-safe action).
The bench range is registered on the name-
plate either as spring range or signal pres-
sure range depending on the actuator. The
direction of action is marked FA or FE, or by
a symbol.
Actuator stem extends FA (Air to open)
Fail-safe position "Valve Closed"
(for globe and angle valves):
Required supply pressure = Upper bench
range value + 0.2 bar, minimum 1.4 bar.
Actuator stem retracts FE (Air to close)
Fail-safe position "Valve 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 + d
p
A
2
4
× ×
×
p D
[bar]
28
EB 8394 EN
Connections