Instruction manual

High Throughput Diffusion Pumps
18
DRAFT 12/23/04
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.
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 48 through page 51.
Table 14 Thermal Cutout Temperatures
Units HS-16 HS-20 HS-32 NHS-35
Water Switch °F 185 185 220 200
Boiler Switch °F 390 390 550 600
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.