Operation
51
130000761_002_A0 - 08/2008 - © Oerlikon Leybold Vacuum
Unplug any connectors only when the mains voltage is switched off
and
the pump does no longer turn (the green LED is off).
3.6
Venting
Refer to Section 3.1 for suited gases.
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 additio-
nal 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.
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 turbomolecular
pump.
The speed of the pressure rise during venting of the running pump will greatly
influence the load on the rotor/stator pack and the bearings. The slower the
pump is vented, the longer the service life of the bearings will be.
The pump must not be vented to pressures above atmospheric pressure.
Warning
Speed
Particles
Pressure rise curve
