Quote: (Originally Posted by Marc T)
does someone have serious information about the maxi O2 level you can safely use in a compressor when the diluent is hélium?
Etherybody know its 40% with nitrogen
With héliox I often use 15% and 20 % without problem and one time 36%
Do you think its dangerous and why?
Mark,
The fraction of O2 you can put through a compressor depends on the compressor and the operator, especially how well maintained the compressor is, O2 is fairly predictable up to 40% pumped to 230 Bar above 40% and 230 Bar things become less predictable.
There is no reason for not pumping bottom mix Heliox through a compressor as this normally has a low O2% but if pumping bailout Heliox eg 50/50 you have to be cautious.
Helium by it's nature will as Joe said cause the compressor to run hotter but it will also find it's way passed the piston and into the crank at the same time "washing" the lubricant as it passes, this can be roughly calculated by putting a known bottom mix through the compressor and checking the helium % after compression.
A good quality well maintained compressor will lose a few % of Helium in the process, a Nitrox compressor will loose less and should have a feed back from the crankcase to the first stage.The danger is when mixing bailout Heliox eg 50/50 the compressor is hotter and the lubrication is diminished by the passing Helium so caution is required.
Now if you pump rich Nitrox immediately after pumping Heliox you could have a major problem even with much less than 40% O2, letting the compressor run for a while between different types of filling will help but again the mix's being pumped and the compressor are variables that have to be considered by the operator.
Cheers