Disassembling The Feedback Arm Assembly And Span Adjuster Assembly; Removing The Feedback Shaft (Cam Shaft); Disassembling The Spool Valve, Action Block, And Gasket - Emerson Fisher 3710 Instruction Manual

Instruction Manual
D101728X012

Disassembling the Feedback Arm Assembly and Span Adjuster Assembly

Note
The zero adjustment locknut and zero adjustment knob are identical parts, key 35.
Note
To identify the span adjuster assembly for 0.4 to 2.0 bar (6 to 30 psig) input range, red color coding appears on the range spring.
1. Remove the feedback arm assembly and flanged bearing (key 22) from the feedback pivot in the positioner base
plate. Then, remove the span adjuster assembly (key 4) by unscrewing the zero adjuster locknut (key 35) and sliding
the span adjustment shaft (threaded rod) from the zero adjustment pivot on the feedback arm (key 21).
2. Inspect the flanged bearing. If the bearing shows signs of wear or damage, replace it.
3. Inspect the zero adjustment pivot. Be sure the pivot rotates freely. If necessary, remove the retaining ring (e‐clip)
(key 34), washer (key 33), and zero adjustment pivot (key 32).
4. After removing the retaining ring, washer, and pivot, inspect the needle bearing (key 25). The needle bearing is
pressed into the feedback arm. If the needle bearing must be replaced, replace the feedback arm assembly (key 21).
5. If necessary, replace the retaining ring, washer, and zero adjustment pivot.
6. Be sure the cam roller (key 23) turns freely. If necessary, remove the shoulder screw (key 24) and cam roller from
the feedback arm and replace them.

Removing the Feedback Shaft (Cam Shaft)

1. Unscrew the cam locknut (key 37) and remove the cam (key 36).
2. Remove the retaining ring (e‐clip) (key 40) and washer (key 39) that hold the feedback shaft (key 38) in place.
3. Grasp the feedback shaft where it extends from the back of the positioner base plate. Pull the feedback shaft from
the base plate, being careful not to scratch the outside diameter of the shaft.
4. Inspect the spacer (key 69) on the shaft. Inspect the flanged bearings (key 17) in the positioner base plate. If the
spacer or bearings show signs of wear or damage, replace them. When re‐installing the feedback shaft, spacer, and
bearings, be sure the shaft rotates freely.

Disassembling the Spool Valve, Action Block, and Gasket

Note
See figure 26. Handle the spool valve body and spool with care. The body and spool are manufactured to precise tolerances and
are prepared as a matched set.
3710 and 3720 Positioners
September 2017
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