Brooks On-Board 8, Installation And Maintenance Instructions Manual

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1-10 ©2013 Brooks Automation Inc. Pub. No. 8040564, Rev. AA, 01/15/13 ECO No. 64541
head provides cooling to the three arrays. Gases are removed from your
vacuum chamber, thereby creating a vacuum when they are condensed or
adsorbed on the cryogenically-cooled arrays.
Cold Head
The cold head consists of a two-stage cold head cylinder (part of the
vacuum vessel) and drive unit displacer assembly, that together produce
closed-cycle refrigeration at temperatures that range from 60 to 120K for
the first-stage cold station and 10 to 20K for the second-stage cold station,
depending on operating conditions. Within the drive unit displacer
assembly, the drive unit actuates the displacer-regenerator assembly
located in the cold head cylinder and thereby controls the flow of helium
into the cold head. Within the drive unit are located the crankcase and drive
motor, which is a direct-drive constant-speed motor, operating at 72 rpm on
60 Hz power and 60 rpm on 50 Hz power.
During operation, high pressure helium from the compressor enters the
cold head at the helium supply connector, and flows through the displacer-
regenerator assembly, crankcase, and motor housing before exiting through
the helium gas return connector and returning to the compressor. Helium
expansion in the displacer-regenerator assembly provides cooling at the
first and second stage cold stations.
Vacuum Vessel and Arrays
The 80K array, as shown in Figure 1-4 or Figure 1-5 , condenses water and
hydrocarbon vapors. The 15K array condenses nitrogen, oxygen, and argon
while the specially processed charcoal of this array traps helium, hydrogen,
and neon. The temperature of the cold head stations to which the 15K array
and 80K radiation shield are attached, is measured by temperature sensors
and transmitted to the On-Board controller for display.
Compressor Gas and Oil Flows
Helium returning from the cryopump cold head enters the compressor, and
a small quantity of oil is injected into the gas stream, thereby overcoming
helium's low specific heat and inability to carry heat produced during
compression. Helium is then compressed and passed through a heat
exchanger for removal of compression-caused heat.
The helium continues its flow through an oil-mist separator and a charcoal
filter adsorber (cartridge), within the compressor, where oil and
contaminants are removed. A differential pressure relief valve in the
compressor limits the operating pressure differential between the helium
supply and return lines, thereby allowing compressor operation without