Agilent Technologies TwisTorr 305-IC SF, User Manual

Page: 239 / 279

Technical Information
Agilent TwisTorr 305-ICQ & 305-IC SF User Manual 239
Pump Used with Corrosive and Oxidizing Gases
To prevent damage to the bearings, an inert gas must flow into the pump body
around the upper bearing towards the forevacuum line. To supply the inert purge
gas (e. g. nitrogen) to the pump through the purge port, connect a gas purge valve
between the pressure regulator and the pump.
Adjust the pressure regulator in order to read a gas flow rate of 0.1 to 0.8 mbar l/s.
CAUTION
To prevent bearing damage, Agilent suggests a minimum purge gas flow rate of
10 sccm (0.17 mbar l/s). This value can be exceeded, according to the process
requirements. Please contact Agilent for specific applications.
When a purge gas is used with the recommended forepump of 15 m 3 /h
(8.82 CFM) a high vacuum pressure in the 10 -8 mbar range can be achieved.
The recommended gas flow maintains a pressure into the pump body higher than
the fore-vacuum pressure. The recommended procedure to vent the system and
the pump avoiding the contact between the pump bearings and the corrosive gas is
described in the following points:
1 Close the corrosive gas flow into the system.
2 Leave the Turbo pump and the backing pump running and the purge gas
flowing, wait for enough time to evacuate the corrosive gas from the system.
3 Turn off the Turbopump and the backing pump.
4 Open the Turbo vent port slowly until to reach atmospheric pressure in the
system.
5 When the Turbo pump and the backing pump are stopped and the system is at
atmospheric pressure, for a better bearing protection it is advisable to leave the
purge gas flowing into the Turbo pump, with the chamber or the Turbo vent
valve open, to avoid system overpressures. If the vent valve can't be kept open,
the backing pump should be left operating.