Instruction Manual
D101728X012
3710 and 3720 Positioners
September 2017
31
D
Vent the actuator loading pressure.
D
Use lock‐out procedures to be sure that the above measures stay in effect while you work on the equipment.
D
Check with your process or safety engineer for any additional measures that must be taken to prevent against process
media.
1. Turn off supply pressure. Release actuator pressure. Remove the positioner cover assembly (key 7).
Note
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.
2. Unscrew the two machine screws (key 3) that hold the spool valve (key 1) onto the action block (key 28). Remove
the spool valve, taking care when separating the spool from the spool flexure on the summing beam.
3. Inspect the three O‐rings (key 2) found between the spool valve and the action block. Remove and replace the
O‐rings, if necessary.
Note
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.
4. Check the function of the new spool valve to be installed. The spool should slide freely in the valve body.
Note
properly engages the summing beam. Start the two machine screws (key 3) so the spool valve is loosely held in
position on the action block.
6.
Before tightening the machine screws holding the spool valve, make sure the end of the summing beam does not
contact the spool.
Rather, the summing beam should contact the
spool head
. If necessary, adjust the position of
the spool valve on top of the action block, making sure the summing beam does not bind on the spool throughout
the full travel of the summing beam. Tighten the two machine screws.
7. Be sure the spool head and summing beam remain engaged, but do not bind up, over the entire operating range of
the input module.