Split Range Operation; Initial Range Spring Extension Procedure For 3570P And 3570Pc Positioners - Fisher 3570 Instruction Manual

Instruction Manual
D200137X012

Split Range Operation

3570 valve positioners are suitable for split range operation. In split range operation, two or more control valves are
operated by one output signal from a single control device. When two control valves are split ranged, one valve
strokes fully with one half the input signal range and the second valve strokes fully with the other half of the input
signal range.
Valve positioners shipped from the factory for split range operation are constructed and adjusted accordingly. If it is
necessary to convert an existing positioner to one suitable for split range operation, consult your
Management sales office
D104021X012). For most changes, a new range spring and possibly a new bias spring will be required. A new range
spring retainer might also be required for 3570, 3570C, 3572, and 3573 positioners.
When corresponding with your Emerson sales office, supply all information possible about the desired operating
conditions and the serial numbers of the control valve assembly. This information will facilitate the proper selection of
the required parts.
To change an existing valve positioner to one suitable for split range operation, refer to the range and bias spring
removal and replacement procedures in the Maintenance section. Be certain the required new parts are on hand
before beginning any maintenance operation.
Initial Range Spring Extension Procedures for 3570P And 3570PC
Positioners
This procedure must be performed whenever the range spring has been changed or the positioner has been removed.
Key numbers used in this procedure are shown in figure 13 except where indicated.
1. With the cap screw (key 87) removed, hook the small ball of the positioner cable (key 91) into the slot of the smaller
portion of the cable spool (key 96). Wind the cable on the spool until the coils of the range spring (key 18, figure 10)
are slightly separated. Be certain the cable is wound so that it comes off the side of the spool opposite the access
opening and that the cable cannot cross itself on the spool.
2. Install the ball end of the actuator cable (key 92) into the slot of the large portion of the spool that is closer to the
access opening. Wrap the cable on the spool as many times as possible, then bring the cable out through the
bottom of the positioner extension. Be certain the cable is wound so that it comes off the side of the spool opposite
the access opening and that the cable cannot cross itself on the spool. Attach the cable to the cable strap (key 93),
leaving approximately a 0.8 mm (1/32‐inch) gap between the cable eye and cap screw head (key 94).
3. With the actuator piston rod completely retracted and the range spring coils slightly separated, attach the cable
strap to the actuator feedback arm. Use the set of cable‐strap holes closest to the range spring. Turn the spring cap
(key 86) one turn counterclockwise and install one cap screw (key 87).
4. Adjust the range spring (key 18, figure 10) to obtain full travel for the input signal range (span adjustment). Refer to
step 7 of the adjustment procedures. Adjustment of the bias spring (zero adjustment) does not need to be done at
this time.
5. Remove the screw from the spring cap and slowly release the torsion spring force by turning the spring cap
clockwise. Disconnect the cable strap from the actuator and remove all range spring extension by rotating the cable
spool.
to determine the new parts required (refer to instruction manual supplement
3570 Positioners
September 2015
Emerson Process
15