Thermal Switches, Initial Vacuum Test

Installation

1-6-4 Electrical Connections (See Figure 1-4 and 1-5, Diffusion Pump Wiring Diagram)

WARNING

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

a.The pump heater has been designed to operate at a certain voltage. Check the heater for cor- rect supply voltage and, in the case of multiphase connections, for load balance by measuring the resistance of each branch. (See pages 1-9, 1-10 for proper resistance.)

b.Make connections to the terminals in the junction box (at the foreline). The use of flexible con- duit is recommended to facilitate removal of the pump for service. The pump should not be operated at more than 5% over the rated voltage. Make connections in accordance with the wiring diagram provided with each pump.

1-6-5 Thermal Switches

The thermal switches have been pre-set at the factory and should not require adjustment. The lower thermal switch is set at 390°F; the upper switch is set at 185°F. Should any thermal switch be thrown out of adjustment, it can be adjusted as follows.

1.Boiler thermal switch

The boiler thermal switch is mounted on the bottom of the brass strap on the side of the pump. The thermal switch should be adjusted, with the pump operating, as follows:

a)After several hours operation, disconnect the lead wires and place an ohmmeter across the terminals of the thermal switch.

b)Turn the adjusting screw until 1⁄16 of a turn either way will make the contact open or close.

c)Turn the adjusting screw clockwise 1⁄4 turn.

2.Cooling water thermal switch

The cooling water thermal switch is mounted on the top of the same brass strap located on the side of the pump. The switch should be adjusted with the pump in operation as follows:

a)Disconnect the lead wires and place an ohmmeter across the terminals of the switch.

b)Turn the switch adjusting screw until 1⁄16 of a turn either way will make the contact open or close.

c)Turn the adjusting screw clockwise 1⁄4 turn.

Thermal switches are to be operated on AC power only and should be connected in series with the coil of the diffusion pump heater contactor.

1-6-6 Initial Vacuum Test

The purpose of this test is to establish the leak tightness of the system, specifically the vacuum connec- tions to the diffusion pump. (To eliminate misleading indications and the masking of leaks by the fluid, the tests should be carried out with the diffusion pump "dry", i.e., before it is charged with the pumping fluid.)

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