GA05141_0702 - 09/2004
67
Operation
Venting
As to suitable gases, see Section 2.6.
Venting Method
The pump must be vented via the purge gas and venting valve or the
vent port when shutting the pump down.
When additionally venting the vacuum chamber, the venting function of the
purge gas and venting valve must be opened before opening the chamber
valve. This will ensure the presence of a higher pressure in the magnetic
bearings compared to the remaining vacuum area. This will prevent parti-
cles, dust or aggressive gases from being forced into the not yet vented
motor chamber of the pump.
Speed of the pressure rise
All turbomolecular pumps may be vented at full speed. However, the pres-
sure must not increase faster than specified through the pressure rise
curve.
The pump must be vented significantly slower when there is the risk of par-
ticles entering into the pump from the process. During venting, the flow
must be of the laminar type in both the vacuum chamber and the turbo-
molecular pump.
The pump must not be vented to pressures above atmospheric pressure.
10
3
mbar
10
2
10
1
10
0
10
-1
10
-2
10
-3
Fig. 50 Curve for safe venting of the MAG;
pressure rise as a function of venting time
010 20304050 60
Time/s
Forevacuum pressure
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