Maintenance
Cold Head Maintenance
Tools required: 5-mm hex key wrench
Slotted screwdriver
Metric socket head torque wrench.
Cold head maintenance can be performed and the displacer can be removed from the
cryopump without relieving the vacuum in the cryopump. Allow the cryopump to warm to room
temperature. Cryopanels need not be removed to withdraw the valve motor and the displacer
from the cold head cylinder. See Figure 3.
Cold Head Removal from the Cryopump
The complete cold head can be removed from the cryopump, if required. The cryopanels have
been removed from the cryopump. Disconnect the gas lines using two wrenches and following
the procedure Disconnect the Gas Lines.
1. Use a screwdriver to remove the M4 x 0.7 flat head, brass screw from the cold head's
second-stage heat station. Remove the diode housing and indium gasket. Inspect the
gasket.
2. Use a 5-mm hex key wrench to remove the socket head cap screws and washers holding
the cold head to the vacuum enclosure. Carefully withdraw the cold head from the
cryopump.
Cold Head Installation into the Cryopump
The seal between the cold head’s warm flange and the flange of the vacuum
enclosure may be either an O-ring or a metal seal. Choose the appropriate
procedure from step 1 below.
Procedure for cold head installation:
1. Examine the O-ring between the cold head's warm flange and the flange of the vacuum
enclosure assembly. Replace the O-ring if it is damaged. Wipe the O-ring with a light coat
of vacuum grease. Insert the cold head into the vacuum enclosure.
A metal seal is not reusable. Discard the used seal and install a new Helicoflex seal. See
the Parts section.
2. Insert the flat washers, lock washers and hex socket head cap screws into the vacuum
enclosure flange and hand-tighten the cap screws.
3. Using a cross pattern, tighten diametrically opposed cap screws. Torque them to 18.6 N-m
(165 in. lbs.).
4. Insert the diode housing into the second-stage heat station. Place the indium gasket over
the hole in the heat station. Install the flat head, brass, M4 x 0.7 x 10-mm long screw.
Tighten with a screwdriver.
5. Reconnect the gas lines. Use two wrenches.
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