Instruction Manual
D101728X012
3710 and 3720 Positioners
September 2017
38
Figure 26. Spool Valve Body and Spool
W5917
SPOOL VALVE
BODY
SPOOL HEAD
SPOOL
1. 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 flexure on the summing beam.
2. Inspect the three O‐rings (key 2) found between the spool valve and the action block. Remove and replace the
O‐rings, if necessary. Lubricate (key 63) O‐rings before installation.
3. Unscrew the four machine screws (key 3) that hold the action block onto the positioner base plate. Lift off the
action block and inspect the gasket (key 29) underneath it. Replace the gasket, if necessary.
4. Check the function of the spool valve. The spool should slide freely in the valve body. If it doesn't, clean the spool
valve or replace it.
Disassembling the Input Module and Summing Beam Assembly
1. Remove the four machine screws (key 3) that hold the input module assembly (key 30) to the positioner base plate.
If the spool valve has not been removed, use care when lifting off the input module and summing beam assembly.
Be sure to properly separate the spool from the spool flexure.
2. Inspect the one O‐ring (key 31) in the positioner base plate. Replace it, if necessary.
CAUTION
Avoid damage to the diaphragm (key 30B) when removing the machine screw (key 30E) that joins the diaphragm
connector and the summing beam assembly. Use a wrench or other tool to hold the diaphragm connector while removing
the machine screw.
3. Remove the machine screw (key 30E) holding the diaphragm connector to the summing beam assembly, taking
care not to twist the diaphragm connector and diaphragm. Use a wrench or other tool to hold the diaphragm
connector while removing the machine screw.