Instruction Manual
D101728X012
3710 and 3720 Positioners
September 2017
32
Figure 22. Spool Valve and Summing Beam
A6044
SPOOL
FLEXURE
LARGER VIEW OF SPOOL HEAD
SPOOL
FLEXURE
SPOOL
HEAD
SPOOL VALVE ASSY
SPOOL RELIEF
SPOOL
HEAD
SUMMING
BEAM ASSY
CLEARANCE
Changing the Span Adjuster Assembly (To Change Positioner Input
Range)
The span adjuster assembly (key 4) consists of the span adjustment knob, span adjustment shaft (threaded rod), range
spring, and washer. The range spring is welded to the washer and the washer is welded to the span adjustment shaft.
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. Unscrew the cam locknut (key 37) and remove the cam (key 36).
Note
The zero adjustment locknut and zero adjustment knob are identical parts, key 35.
2. Loosen the zero adjustment locknut and turn the zero adjustment knob (key 35) until the range spring is free from
the summing beam. Move the feedback arm (key 21) until the range spring falls away from the summing beam.
Note
The feedback pivot cannot be removed from the positioner base plate.
3. Remove the retaining ring (e‐clip) (key 27) which holds the feedback arm assembly (key 21) onto the feedback
pivot. Remove the washer under the retaining ring and pull the feedback arm from the pivot.
4. Remove the span adjuster assembly from the feedback arm by removing the zero adjuster locknut and sliding the
span adjustment shaft (threaded rod) from the zero adjustment pivot on the feedback arm.
5. Remove the zero adjustment knob from the span adjuster assembly. Install the zero adjustment knob on the new
span adjuster assembly.