Maintenance
3. Install the inlet louver after checking that the indium gaskets are in place. Install the
stainless steel flat washers and lock washers.
Torque the M4 x 0.7 hex nuts to fasten the inlet louver to the first-stage cryopanel to
1.4 N-m (12.5 in. lb).
This completes the procedure for reassembling the cryopanels.
Clean the Relief Valve
EXPLOSION HAZARD. AVOID INJURY. Establish a cleaning schedule based
on pressure rise to keep the relief valve free of dirt generated during the vacuum
process.
Tool required: Flat nose pliers.
The relief valve is designed to open and vent gases if the pressure rises to 7 kPa (1 psig).
The valve should be checked and cleaned if dirt prevents proper seating and causes leaks,
indicated by the inability to attain an adequate vacuum level when rough pumping.
1. If the relief valve leaks, remove it by unscrewing the knurled cap.
2. Remove the snap ring and the spring. Disassemble the relief valve assembly. Remove
both O-rings.
3. Clean the O-ring seats and the entire assembly with a solvent on a clean, lint-free cloth.
Blow the parts dry with dry, nitrogen gas.
4. Wipe both O-rings with a dry, clean, lint-free cloth. Examine both and replace them
if they are damaged. Be sure the seating O-ring has no dirt inclusions embedded in its
surface. Apply vacuum grease sparingly to the O-rings. Use only enough grease to give a
shiny appearance to the O-rings. Remove excess grease with a dry, clean, lint-free cloth.
5. Reassemble the valve. Reinstall it, turning the knurled cap only hand tight.
Clean the Relief Valve’s Filter Screen
Inspect the filter screen whenever the cryopump’s first stage cryopanel is removed. If there is
any visible debris accumulated on the screen, remove the relief valve as described above. Blow
dry, compressed air into the open end of the relief valve elbow to remove any accumulated
debris from the screen. If this procedure does not remove all the debris from the screen,
replace the relief valve base subassembly.
Rupture Disc
A rupture disc is normally supplied with copper-gasketed cryopumps. Because no threads or
O-rings interconnect with the vacuum area, rupture discs form a tighter seal than do relief
valves.
As the cryopump warms to ambient temperature, the rupture disc automatically bursts if the
cryopump chamber pressure reaches 124 kPa (18 psia). Once the disc has failed, the
assembly must be replaced.
1. Remove the six socket head cap screws on the utility port flange.
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