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Startup Procedure
To start the pump:
1. Evacuate the diffusion pump using a mechanical
roughing pump to below 0.5 Torr (0.67 mbar). The
diffusion pump will not function unless the discharge
pressure is less than the tolerable forepressure.
2. Turn on the cooling water supply to the pump
body and check that adequate flow is provided by
examining the amount of water discharged at the
visual drain points.
CAUTION
To prevent harmful collection of
condensate on the boiler plate, heater,
and heater terminals, do not operate the
Quick Cool coil when the pump is cold
or out of service.
3. Switch on the power to the diffusion pump heater.
4. Check inlet and forepressure performance by means
of the system instrumentation.
Humid Environments
Due to their inherent design, diffusion pump heaters
absorb moisture. This results in a decrease in heater insu-
lation resistance (higher leakage current). Under normal
conditions, the decrease in insulation resistance is a
momentary condition that occurs on startup. The amount
of moisture adsorbed is depends on the temperature,
humidity, and the length of time the heaters have been
exposed to this environment without power being
applied. If diffusion pumps are started in high humidity
environments, the heaters may be damaged on startup at
full power. To overcome the effect of moisture absorbed
in the heaters, start pumps at a low line voltage, e.g., 50%
of line voltage, for a period or time to slowly expel any
moisture.
High Throughput Diffusion Pumps
40
Shutdown Procedure
WARNING
1. Releasing 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 fluid and greatly increases
the risk of an explosion.
2. Boiler temperatures reach 530° F
(275 °C) which can cause serious
burns. Always check that surfaces
have cooled to near room tempera-
ture before touching them.
To shut down the pump:
1. Close the inlet valve on the system, if equipped.
2. Turn off the power to the heaters.
3. For pumps equipped with the optional Quick Cool
Coil, admit water into the coil.
4. Continue to flow cooling water through the pump
(and Quick Cool Coil, if equipped) for at least the
time period listed under "Cooldown Time Without
Quick Cool With Quick Cool" in Table 4 on
page 13.
5. Once the pump is cooled, shut off the mechanical
backing pump.
6. Air release the pump.
7. Continue cooling water flow until the pump is at
room temperature, then shut off the water supply.
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