Flowserve 3400MD Digital Positioner - Manual (Page 44)

Logix 3400MD Digital Positioner FCD LGENIM3404-08-AQ –5/15
44
Figure 20: Main Housing Vent
Replacing the User Interface Board
To replace the user interface board, refer to Figures 6, 12, 16 and 22
and proceed as outlined below. The following tools are required:
• Phillips screwdriver
c DANGER: Observe precautions for handling electrostatically sensi-
tive devices.
1. Make sure the valve is bypassed or in a safe condition.
2. Disconnect the power and air supply to the unit.
3. Remove the main cover.
4. Remove the plastic board cover by removing the three retaining
screws (see Figure 16).
5. Remove the retaining screw from the main PCB assembly and
lift the main PCB out of the housing (see Figure 16). It is not
necessary to disconnect all of the wires, only the UI plug.
6. Remove the user interface cover.
7. Disconnect the field wiring from the user interface board termi-
nals and remove the three screws that hold the user interface
board in the housing (see Figure 6).
8. Remove the user interface board, carefully pulling the wiring
through the bore.
9. Verify that the O-ring is in place in the counterbore in the
positioner housing, or on the plug on the back of the UI tray.
10. Feed the wires on the back of the new user interface board
through the passageway into the main chamber of the housing.
11. Set the user interface board in place and secure with three screws
(see Figure 6).
12. Reconnect the field wiring to the user interface board terminals.
13. Install the main PCB into the housing. Insert the retaining screw
through the board into the threaded boss and tighten evenly,
using a Phillips screwdriver. Do not overtighten.
14. Install the plastic board cover. Insert the three retaining screws
through the plastic cover into the threaded boss and tighten
evenly, using a Phillips screwdriver. Do not overtighten (see
Figure 16).
15. Reinstall the UI wire connection (see Figure 12).
16. Reinstall all covers.
9 Optional Vented Design
NOTE: See Figures 19 and 20.
A standard Logix 3400MD 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. This piping system may cause some positioner back
pressure in the main chamber (from the modulator and regulator)
and spool chamber (from the actuator). Back pressure limitations are
described below.
Two chambers must be vented on the Logix 3400MD positioners:
the main housing chamber and the spool valve chamber (Figures 20
and 21). The main chamber vent is located on the backside of the
positioner (see Figure 20). Vented-design Logix 3400MD positioners
are supplied from the factory with a fitting installed in the main
chamber vent. Connect the necessary tubing/piping to this fitting to
route the exhausted natural gas to a safe environment.
The maximum allowable back pressure from the collection device on
the main housing vent is 2.0 psig (0.14 barg). Vent flow rate is
0.5 std ft
3 /min (1.4 std liter/min).
c DANGER: The back pressure in the main housing must never rise
above 2.0 psig (0.14 barg).
The spool valve chamber (see Figure 21) must also be vented
through the spool valve cover. Vented-design Logix 3400MD
positioners are supplied from the factory with a fitting installed in
the spool valve cover (item SKU 179477). Connect the necessary
tubing/piping to this fitting to route the exhausted natural gas to
a safe environment. The maximum allowable back pressure in the
spool valve chamber is 8 psig (0.55 barg). Pressures greater than
8 psig will cause vented gas to leak past the spool cover O-ring to
the atmosphere and will result in overshoot of the positioner.