Connecting The Purge Tube - Emerson FISHER 3710 Instruction Manual

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Instruction manual (56 pages)

Table of Contents

Instruction Manual

Form 5300

July 2005

LONG-BLADED SCREW

DRIVER THROUGH VENT

W6073/IL

installs in the vent opening in the positioner base

plate. When the purge tube is used, it relays actuator

exhaust pressure from the positioner into the

actuator housing.

Within the actuator and positioner assembly,

exhaust pressure takes the following course:

D The actuator exhaust pressure vents from the

actuator through the positioner spool valve into the

positioner case.

D The exhaust pressure then exits the positioner

case through the vent opening.

D The purge tube carries the exhaust pressure

into the actuator housing.

D The exhaust pressure then purges the actuator

housing and dissipates from the housing.

Most Fisher actuators do not have vent openings.

The exhaust pressure simply dissipates from within

the actuator housing. However, the Types 1051,

1052, and 1061 actuators feature an operational

screened vent connection when a metal access

plate is specified for the actuator housing.

Figure 13. Mounting the Positioner Base Plate with Purge Tube

3710 and 3720 Positioners

PURGE TUBE (KEY 58)

O-RINGS (KEY 59)

When using the purge option, remember: The

actuator and positioner assembly is not airtight.

However, if you use the optional purge tube to

connect the positioner to the actuator and the

actuator has a vent opening, leave open the 1/4-inch

NPT vent connection in the actuator housing to

prevent pressure buildup in the positioner case.

If the 1/4-inch 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 Fisher sales

office.