Logix
®
Digital Positioners FCD LGENIM0110-0 05/16
flowserve.com
21
19.2 Connect Supply Port
The positioner ports are threaded with ¼ NPTF.
In order to maintain the recommended air quality, a
coalescing filter should always be installed in the supply
gas line. An air filter is highly recommended for all
applications where dirty air is a possibility. The positioner
passage ways are equipped with small filters, which
remove medium and coarse size dirt from the pressurized
air. If necessary, they are easily accessible for cleaning.
A supply regulator is recommended if the customer will be
using the diagnostic features of the Logix
®
but is
not required. In applications where the supply pressure is
higher than the maximum actuator pressure rating a supply
regulator is required to lower the pressure t
o the actuator’s
maximum rating.
19.3 Vented Design
A standard Logix
®
positioner is vented directly to
the atmosphere. When supply air is substituted with sweet
natural gas, piping must be used to route the exhausted
natural gas to a safe environment.
The housing chamber exhaust port is located on the
backside of the positioner. The actuator exhaust port is
located on the front of the positioner. Both ports are
tapped with ¼ NPTF and covered with a protective cap. To
control vented gas, remove the caps and connect the
necessary tubing/piping to these ports. See
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.
This piping system may cause some positioner back
pressure. Back pressure in the housing chamber is from
the modulator and regulator. Back pressure in the exhaust
port is from the actuator.
The maximum allowable back pressure from the housing
chamber is 0.14 barg (2.0 PSIG). For flow rates, see
section 16.3 Air Supply.
The maximum allowable back pressure from the exhaust
port is 0.55 barg (8.0 PSIG). Higher pressure may result in
decreased performance. For output flow rates, see section
16.2 Pneumatic Output.
CAUTION:
The back pressure in the main housing
must never rise above 0.14 barg (2.0 PSIG). This could
cause the positioner to become unresponsive under some
circumstances
CAUTION: The natural gas used must be sweet
natural gas. Use of sour natural gas may cause positioner
to fail prematurely.
Figure 16: Exhaust Vents
