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Operation
2-2
a. Switch off the power to the diffusion pump heaters.
b. Admit cooling water to the quick-cool coil if necessary and continue to circulate it until the
pump body just above the boiler heat shield can be touched (approximately 130°F or 54°C).
In valved systems which have tight inlet and foreline connections, it is possible to close valves
to isolate the diffusion pump at inlet and discharge, to air-release the remainder of the sys-
tem, shut off the heat to the diffusion pump, and stop the mechanical pump. With this method,
the quick-cool coil does not have to be used. However, the water flow through the pump must
be maintained until the boiler cools down below approximately 300°F (150°C).
d. Check inlet and forepressure performance by means of the system instrumentation.
e. During operation, the gas load at the inlet of the diffusion pump should not exceed the maxi-
mum throughput capability of the pump. This means that the pressure at the inlet flange
should not (except in transient conditions) exceed approximately 1 x 10
-3
Torr (.133 Pa). Dur-
ing operation, the discharge or fore pressure must be below the specified tolerable forepres-
sure.
2-2 SHUTDOWN PROCEDURE
WARNING
_____________
Boiler temperatures reach 530°F (275°C) which can cause serious
burns when touched. Always ensure surfaces have cooled near room
temperature before touching them.
CAUTION
________
Do not operate the quick-cool coil when the pump is cold or out of ser-
vice to prevent harmful collection of condensation on the boiler plate,
heater, and heater terminals.
Air release or admitting air to a pump with a hot boiler, especially when it is under vacuum, permits a
strong oxidizer to contact the hot pump oil and thereby increases the risk of an explosion.