Flowserve 1878 Double-Disc Gate Valve - Manual (Page 12)

12
9.0 MAINTENANCE INSTRUCTIONS (Continued)
9.1.1
Disassembly (Continued)
(g) The Lower Wedge (071) can now be separated from the Upper
Wedge (069). When separating the two wedges, take care that the
Wedge Spring (269) does not fly out and become lost.
9.1.2
Assembly
Assembly of the valves is simply the reverse of disassembly. Prior to
reassembly, read the following special instructions.
(a) All dirt, scale and foreign matter should be removed from inside the
valve body and bonnet.
(b) Check the seating surfaces to determine that scratches or minor
imperfections do not exist on the discs or seat rings. If any are
evident, lap these surfaces until none are visible. (Reference Para.
9.3.)
(c) When replacing the Bonnet Studs and Nuts (200 & 230) consult the
applicable drawing or Section 11.0 for correct torque to assure
tightness of the seal. Prior to tightening, the studs and nuts should
be lightly lubricated with a nuclear grade lubricant.
(d) The nuts should be tightened evenly using a criss-cross pattern as
shown in Figure 2. Tighten all of the nuts to 1/3 of the recommended
value initially. Then repeat the sequence raising the torque to 2/3 of
the full torque.
(e) Finally, torque all of the nuts to the recommended value following the
criss-cross pattern. It is essential that the flange faces remain
parallel and all of the bolting has uniform tension. Failure to achieve
this may cause gasket weepage when the joint is subjected to
operating pressures and temperatures.
NOTE: As an extra aid to ensure proper bolt tightening, the valve
bonnets have been permanently marked with sequence
numbers for bolt tightening.