Disassembling And Assembling The Bypass Valve - Fisher 3660 Instruction Manual

3660 and 3661 Positioners
September 2015
8. Carefully lift the flapper spring at the location shown by key 10. Install the flapper (key 9) so that the desired letter
(D or R for direct and reverse) is nearest the adjusting screw (key 18). When inserting the flapper, be sure the end of
the flapper engages the grove in the end of the screw, and that the flapper spring (key 10) sets into the V‐notches of
the flapper.
9. With the flapper (key 9) in place, visually ensure that it is aligned parallel to the cover plate assembly (key 8) as
shown in figure 22. Realign if necessary by repositioning the flapper spring (key 10). The flapper alignment affects
the performance of the positioner. Be careful not to damage the lapped surfaces on the cover plate and nozzle.
10. Reinstall the range spring (key 30). Push the feedback lever assembly (key 19) back into position and retighten the
retaining screw (key 19P).
11. With the output at supply pressure, check the output diaphragm assembly joints for leaks.
12. Refer to the Calibration section for the calibration procedure.

Disassembling and Assembling the Bypass Valve

During the following bypass valve disassembly and assembly procedures, refer to figure 23, unless otherwise
indicated.
Figure 23. Fisher 3660 Bypass Valve
11B3925‐B
1. Remove all pressure from the positioner. Disconnect the supply, instrument and output tubing.
2. Remove the two cheese head screws (key 47). Lift the bypass valve from the positioner being careful not to loose
the three O‐rings (key 49).
3. Remove the plastic wire tie (key 79) and retaining ring (key 46).
4. Using a gentle pulling and turning motion, slide the bypass lever assembly (key 42) from the bypass body (key 41).
5. Inspect the O‐rings (keys 43, 44, 45 and 49) for nicks and wear, and replace as necessary. When installing new
O‐rings (keys 43, 44 and 45) on the shaft of the bypass lever assembly, lubricate them sparingly using lubricant
(key 48).
6. Install the bypass lever assembly (key 42) into the body assembly (key 41) using a gentle turning and pushing
motion to avoid nicking an O‐ring.
7. Install the retaining ring (key 46).
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Instruction Manual
D101402X012