Maintenance
3-7
b
Remove the heater cover and insulation from the bottom of the diffusion pump.
c
Remove the nuts holding the clamping plate.
d
Lower the entire heating unit (heater element, clamping plate and heater shield, see
Figure 3-3) until it is off the mounting studs.
e
Coat the boiler studs with anti-seize compound such as FEL-PRO-C-5A or common milk
of magnesia.
f
Assemble the new unit (heater element, clamping plate, and crush plate).
g.
Support the heating unit by the clamping plate, line up the holes with the boiler studs, and
push the unit up against the boiler plate. Use two nuts finger-tight to hold it in place.
h.
Screw on the remainder of the nuts finger-tight, then tighten the nuts evenly up to 250 inch-
pounds of torque.
i
Label the heater leads according to the schematic diagram, then run the wires around the
periphery of the pump, under the wire retaining clips, into the conduit, and up into the junction
box. Connect the leads to the terminal strip then replace the elbow cover plate.
j
Replace the heater cover and insulation.
CAUTION
Should it be necessary to use a new wire in the following step, it is
important that no. 10 stranded nickel wire with high-temperature insula-
tion is used. The terminal lugs must be solid nickel. If copper or copper-
plated wire and/or lugs are used, they will oxidize rapidly because of the
high temperature and the terminals will overheat and fail.
Figure 3-3. Heater Element Assembly