You can use the pump to pump oxygen and water vapour, subject to the following conditions :
·
Oxygen
The oxygen concentration must be less than 20% by volume.
·
Water vapour
You must ensure that vapour does not condense inside the pump;
refer to Section 3.7.1.
If you wish to pump a gas not in the list above, contact your supplier for advice. If you do not
contact your supplier, you may invalidate the warranty on the pump. The EXT250M is not
suitable for pumping explosive, aggressive or corrosive gases.
2.2.2
EXT250M with gas purge
When purged with an inert gas, the EXT250M pump can be used to pump oxygen in
concentrations above 20% by volume.
The recommended purge gas flow for typical applications is 25 sccm (0.42 mbar l s
-1
, 42 Pa l s
-1
).
If you pump oxygen-rich gas mixtures, adjust the purge gas flow to dilute the oxygen
concentration to less than 20% by volume.
2.3
Vent gas specification and vent control data
Although the pump may be vented to atmospheric air, high relative humidity of the air may
greatly increase the subsequent pumping time. To reduce pump-down times you should vent
the pump with dry, clean gases.
Vent gas
Dry air, nitrogen, argon or other
inert gases
Maximum dew point at atmospheric pressure
- 22
o
C
Maximum size of particulates
1
m
m
Maximum concentration of oil
0.1 parts per million
Maximum allowed rate of pressure rise
See Figure 2
Vent-valve orifice diameter
See Tables 4 and 5
Maximum pressure
2 bar (gauge), 29 psig, 3 x 10
5
Pa
2.4
Purge gas specification
Purge gas
Dry nitrogen, argon or other
inert gases
Maximum dew point at atmospheric pressure
-22
o
C
Maximum size of particulates
1
m
m
Maximum concentration of oil
0.1 parts per million
Purge gas flow (when required)
20 to 100 sccm (0.33 to 1.67 mbar l s
-1
,
33 to 167 Pa l s
-1
)
Recommended purge gas flow
25 sccm (0.42 mbar l s
-1
, 42 Pa l s
-1
)
Maximum allowable purge gas supply pressure
2 bar (gauge), 29 psig, 3 x 10
5
Pa
EXT250M Turbomolecular Pump
7
