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To wire the pump:
1. Check the heater for correct supply voltage and find
the appropriate wiring diagram. The correct voltage is
shown.
2. Check load balance by measuring the resistance of
each branch. The heater resistances are given on
their respective wiring diagrams.
3. Make the connections to the terminals in the
electrical main junction box at the foreline shown in
the appropriate outline drawing. Use flexible conduit
to make it easier to remove the pump for service.
4. Connect the earth ground wire directly to the
aluminum set screw ground lug.
5. Connect the input wires to the terminal block
positions L1, L2 and L3(& N). For added safety, to
prevent the wires from being disconnected, secure
these wires together with the earth ground wire inside
the junction box with a tie-wrap, similar to what has
been done with the heater wires.
6. Wire the thermal switches to a control mechanism to
ensure that power to the pump is shut off if one of the
switches opens. The thermal switch wires can be
found in the electrical box.
7. Complete the wiring of the pump and double-check
that the proper terminal arrangement has been used
for the source voltage at the site.
High Throughput Diffusion Pumps
25
Overheating: Detection by
Thermal Switches
An overheat condition is detected by two normally closed
thermal cutout switches, one of which monitors the boiler
temperature while the other monitors the water tempera-
ture. These switches are set at the factory and do not
require adjustment. The cutout temperatures for the water
and boiler switches are given in Table 14.
Table 14 Thermal Cutout Temperatures
Units HS-16 HS-20
Water Switch
°F
Boiler Switch
°F
Wire the pump such that if the contacts open on either
the boiler or the water switch, power to the pump shuts
off. If this happens during operation, check for one of the
failure conditions listed below. When the problem has
been corrected and the temperature lowered, the thermal
switch automatically resets.
A rise in pump temperature can be caused by:
❑
Failure of cooling water flow
❑
High inlet pressure
❑
Low fluid level in the boiler
If you determine that the pump has not overheated and
that the thermal switch has failed or drifted out of calibra-
tion, replace the switch with the device listed for your
pump type in the appropriate Replacement Parts table,
page 53 through page 56.
CAUTION
Thermal switches set to measure the
temperature in the diffusion pump fluid
are not designed to protect against
overheating or backstreamed
mechanical pump fluids.
HS-32
185
185
220
200
390
390
550
600
NHS-35
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