4.6
Venting
As to suitable gases, see Section 4.1.
Venting Methods
There are three different methods of venting the turbomolecular pump.
In the case processes requiring a purge gas, the pump must be vented via
the purge gas and venting valve 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 area of the ball
bearings compared to the remaining vacuum area. This will prevent particles,
dust or aggressive gases from being forced through the bearings into the not
yet vented motor chamber of the pump.
Cautious venting of the pump is possible from the high vacuum side, since
here the bearing forces will be lowest. When doing so, no free jet of gas must
be allowed to form on the rotor so as to avoid exposing the rotor to addi-
tional forces.
When venting the pump through its foreline connection, neither oil nor par-
ticles may be entrained in the gas flow from the forevacuum side into the
pump.
Operation
27
GA05118_1502 - 12/2006 - © Oerlikon Leybold Vacuum
0
40
35
30
25
20
15
10
5
s
10
-2
10
-1
10
3
10
2
10
1
mbar
For
evacuum pr
essur
e
Time
TURBOVAC 35 LS(2), 50
TURBOVAC 151, 361
TURBOVAC 600, 1000
Fig. 9 Curves showing the pressure rise
Purge gas and venting valve
High vacuum side
Foreline connection
