Table des Matières
Publicité
PUMP TROUBLESHOOTING
SYMPTOM
1) - Slow starting
2) - Slow starting (more than 30
minutes).
3) - Slow pump-down due to long
exposure of viton parts to air.
4) - Slow pump-down due to ab-
sorption of vapours on pump and
system walls.
5) - Slow starting or slow pump-
down.
6) - Current higher than expected
at any given pressure.
7) - System fails to achieve desired
UHV vacuum pressure.
8) - System fails to achieve desired
UHV vacuum pressure.
POSSIBLE CAUSE
Starting vacuum pressure too high.
Air leaks which limit pressure to
-6
above 10
Torr (mbar) and cause
longer starting time.
Viton releases considerable gas
after long exposure to air. (A bell-
jar system which reached 1.5 x 10
8
-8
Torr (2 x 10
mbar) in 24 hours
after 30 minutes air exposure, will
-8
only reach 7.5 x 10
Torr (1 x 10
mbar) in 24 hours after 20 hours
air exposure).
Vapours and gases admitted to a
system are absorbed on the walls
of the system and pump. Subse-
quent reduction in pressure de-
pends on the rate of depletion of
this vapour. Heavy hydrocarbons
are most troublesome because of
their relative low vapour pressure
and are very difficult to remove,
even by baking.
High voltage feedthrough is leak-
ing.
Ion pump leakage current causing
higher pressure reading.
System not fully baked. Water va-
pour limits base pressure
System not appropriately cleaned
for UHV. Excessive outgassing
from walls limits base pressure.
19
TECHNICAL INFORMATION
CORRECTION PROCEDURE
Reduce pressure to 10
-3
ommended 10
Torr minimum.
Leak check the vacuum system
with a helium leak detector.
With the system under vacuum,
pump for several days, or heat to
-
100-150°C for up to 15 hours.
-7
Bake the system walls, thereby
accelerating the desorption proc-
ess. Baking mobilizes the vapours
so they can be cracked and
pumped by discharge (see para.
"BAKEOUT OPERATION").
Replace the feedthrough.
Highpot the pump.
Bake the system walls, thereby
accelerating the desorption proc-
ess. Baking mobilizes the vapours
so they can be cracked and
pumped by discharge (see para.
"BAKEOUT OPERATION").
Clean all components for UHV and
bake the system again.
87-900-063-01(C)
-5
Torr rec-
Publicité
Table des Matières
