Installation and Operation
22
P1700040
5.8 Oil for Drawing off Oxygen
WARNING!
Pump should be not used for oxygen service! Oxygen at atmospheric pressure is
exceptionally dangerous!
For drawing off oxygen containing mixtures or pure oxygen the following must be taken into
consideration:
Mineral oils are flammable and not suitable for oxygen contents above 30%
The more they oxidise, the quicker they lose their properties. For this reason they
only can be used up to an oxygen percentage of maximum 30 per cent in the
medium to be delivered.
For higher oxygen contents synthetic oils have to be used, i.e., LABOVAC 13
(PFPE)
In order to prevent any accumulation of oxygen in the discharge space, neutral gas such as nitrogen
may be let in through a special inlet assembly. The percentage of oxygen is being reduced. The added
amount of gas should be 5 times as much as the percentage of oxygen.
For pumping oxygen please order a CRVpro 65 specially prepared with PFPE oil (Order no. 3657T-
01-03)
CAUTION! / WARNING!
There is a risk of explosion when pumping oxygen at a concentration above
30 percent.
5.9 Gas Ballast Control
The principle of the gas ballast is described in chapter 3.4.7 Gas Ballast.
To open or close the gas ballast turn the gas ballast switch to the position open or close.
Operation with gas ballast when drawing off condensable vapours
We suggest operation
with the gas ballast valve open, provided that the composition of gas in the
vacuum pump to be drawn off is not known and cannot be ruled out.
If condensable gas and vapours are to be delivered, the latter or their condensates will mix with the oil.
As a result of this, the pump performance will degrade.
5.10 Trap installation and maintenance
Where corrosive vapours or large quantities of condensable vapours are evolved from vacuum
processing, a cold trap may be used in the connecting line to the pump. It will help prevent damage to
the pump mechanism and reduce oil contamination. The cold trap, immersed in a suitable Dewier
flask, is installed so that the vapours may come in contact with the surfaces of the trap and condense.
Commonly used refrigerants are liquid nitrogen or dry ice and acetone. The refrigerant to be used
depends upon the freezing point of the contaminants. A variety of cold traps are available
– see
chapter 8 Accessories.
When using a cold trap the refrigerant should be maintained at a high level in the flask to keep the trap
at a uniformly low temperature. If the trap is rewarded it may allow re-evaporation of the condensate.
The refrigerant add tube on the liquid nitrogen trap should not be obstructed as the refrigerant boil-off
