Maintenance

WARNING

High voltages (up to 480V) can kill. Always break the primary circuit to the power supply before starting to work on the heater and/or its wiring.

CAUTION

Poor clamping resulting in inadequate thermal contact may result in reduced heater life and poor pump performance. Tighten nuts finger- tight on clamping plate, then gradually and evenly tighten them to 250 in-pounds of torque.

1Determine which heater element has failed at the junction box, then disconnect the two corre- sponding leads from the terminal strip. Pull the leads out of the terminal box then out the elbow cover plate.

2Remove the heater cover from the bottom of the diffusion pump. Move the insulation to expose the faulty heater(s).

3Remove the nuts holding the clamping plate.

4Lower the entire heating unit (heater element, clamping plate and crush plate) until it is off the mounting studs.

5Apply an anti-seize compound such as FEL-PRO-C-5A or common milk of magnesia to the studs as needed.

6Assemble the new unit (heater element, clamping plate, and crush plate).

7Support 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.

8Screw on the remaining nut finger-tight, then tighten all nuts evenly up to 250 inch-pounds of torque.

9Label the heater leads according to the schematic diagram, then run the wires into the con- duit and up into the junction box. Connect the leads to the terminal strip then replace the elbow cover plate.

10Replace the insulation and heater cover.

CAUTION

Should it be necessary to use a new wire, it is important that no. 14 stranded nickel wire with high-temperature insulation is used. If copper or copper-plated wire is used, they will oxidize rapidly because of the high temperature and the terminals will overheat and fail.

3-10