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Frank, those of us (ie/ almost everyone) who mix trimix (not heliar) use partial pressure blending of oxygen, helium and air. So, all the issues with nitrox exist with trimix. At 07:52 PM 4/7/1999 +0200, you wrote: >S I L E N T I M M E R S I O N wrote: > >> Frank, >> >> >I can understand that someone doesnt want to do the more dangerous Nitrox fills, but with >Trimix... >> >> What's the dangerous part????? >> Care to explain? > >There are several ways to produce Nitrox these are continous blending, molecular weight mixing, >nitrox membrane and partial pressure filling. The typical home brewer will use partial pressure >filling which is the least expensive. > >The main hazard of Nitrox filling results from the oxidizing properties of oxygen and its abiltiy to >accelerate combustion. Oxygen will lower the ignitation temperature of any fuel and increase the >combustion rate dramaticaly. The danger is that some fuel (gaseous hydrocarbons, oil, grease, >lubricants) inside the tank or filling setup will explode. You can imagine that an exploding tank is >not healthy (btw. explosion pressure of a hand granade is ~ 1200psi). > >How does partial pressure filling work? > - Transfill some amount of Oxygen with a whip to the scuba tank > - Fill the tank with air from a compressor > >So where are the problems? > - All parts that will see high pressure oxygen must be oxygen serviced, this includes tanks, valves, > regulators, filling whip, pressure gauges > - The air which is used for topping must be free of hydro cabon fumes and oil. A typical requirement > is less than 25ppm hydrocarbons and 0.1mg oil mist per m3. > >Common failures > - A piece of equipment is not oxygen serviced > - The filling air contains to much oil mist > - Oxygen tranfilling is done to fast (this will warm up the scuba tank due to adiabatic compression) > >For partial pressure mixing it is vital that you use an extra nitrox filter stage after the compressor. >This filter should be equiped with a check valve that avoids back flow of nitrox/oxygen into the >filter and compressor system. >Filling an oxygen serviced tank only ONCE on a compressor without the extra nitrox filter may put >enough oil into it to create a serious DANGER next time. > > >Regards, > >Frank > >P.S. You should have heard about that in your Nitrox course. > > >-- >Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. >Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > ----------------------------------------------- Kevin Connell <kevin@nw*.co*> NW Labor Systems, Inc http://www.nwls.com And I suppose you want a user interface with that..... ----------------------------------------------- -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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