Instruction Manual
D101728X012
3710 and 3720 Positioners
September 2017
22
If the 1/4 NPT vent connection is available, a vent line can be installed from the actuator. However, the
valve/actuator/positioner assembly is not airtight. Maintain adequate ventilation and observe other safety measures.
For help in selecting the purge option for positioner/ actuator combinations, contact your
Local Business Partner
Connecting the Purge Tube
With an integral mounting, a purge tube (key 58), with two O‐rings (key 59), can be used to relay actuator exhaust
pressure from the positioner into the actuator housing. If the current actuator cover plate does not have the positioner
mounting holes and purge tube knockout, order a new cover plate. See the parts list for the specific actuator cover
plate required for each actuator.
1. The actuator cover plate features a purge tube knockout. Locate the knockout and use appropriate tools to open
this hole in the cover plate.
2. Install the actuator cover plate and then insert the purge tube with O‐ring into the purge tube hole in the cover
plate.
Note
When mounting a positioner to an actuator with the purge tube installed, guide the purge tube into the vent opening in the
positioner base plate by removing the vent screen (key 41) and then inserting an appropriate tool such as a screwdriver through
the vent opening into the purge tube.
When the positioner is secured to the actuator, install the vent screen.
3. Before mounting the positioner, be sure the second O‐ring is properly fitted to the end of the purge tube. Use care
when mounting the positioner. Be sure the purge tube with O‐ring fits into the vent opening on the rear of the
positioner base plate.
4. Secure the positioner to the mounting plate using the (hex) socket head cap screws (key 46).
5. Install the vent screen in the positioner base plate.
Electrical Connection for the 3720 Positioner
WARNING
In explosion‐proof applications, disconnect power before removing the converter housing cap.
In Class I, Division 1 explosion‐proof applications, install rigid metal conduit and a conduit seal no more than 457 mm
(18 inches) from the converter. Personal injury or property damage may result from explosion if the seal is not installed.
For intrinsically‐safe installations, refer to the loop schematics shown in figures 34 and 35 or to instructions provided by the
barrier manufacturer for proper wiring and installation.
Select wiring and/or cable glands that are rated for the environment of use (such as hazardous area, ingress protection and
temperature). Failure to use properly rated wiring and/or cable glands can result in personal injury or property damage
from fire or explosion.
Wiring connections must be in accordance with local, regional, and national codes for any given hazardous area approval.
Failure to follow the local, regional, and national codes could result in personal injury or property damage from fire or
explosion.
