Rebreather World - View Single Post

Genesis · 2nd January 2007, 16:49

To get an ACCURATE correlation you need both the pressure at the time of the measurement AND the temperature of the gas at the measurement point.

The former is pretty easy, but the latter is not (accurately.) Without the temperature you cannot correlate the RH to an absolute (mg/m^3) value.

Monitoring online does not tell you that you are within dewpoint specs generally (the big risk here is taking a tank filled in the middle of summer, and letting it sit until winter, then diving with it - you could have free condensed water in the tank, and thus have corrosion problems if that's a steel cylinder, or have problems in cold water with a regulator first-stage freeze)

What it does tell you is that your dessicant is working and thus your activated carbon is still effective in removing hydrocarbons.

That is the point of online monitoring with an "eyeball" - to know that you are still effectively removing contaminents from your product gas.

Note that a lot of the "compressor guys" will sell you 20/40% cards. Those are completely worthless as once the 20% one turns your stack is already rubbish and by the time the 40% one turns you're not only pumping water-laden gas but LOTS of oil vapor as well!

For those who say "that doesn't work" - yes it does. I've verified my setup with a montoring test and meet OCA (Mod-J) air quality standards just as my indicator card says I need to change the primary filter stack. Most "commercial" shops change the filters and then test for their "certificate." That, of course, is backwards - they should be testing with used filters at maximum life so they see the worst case - not the best case!

The shop is concerned with getting sued if they are out of complience. I'm concerned with not blowing up or killing myself while underwater due to contaminated breathing gas.

Try diving in the Caribbean sometime if you want to breathe truly foul "air". I just got back from there a week or so and found it basically impossible to find air that didn't have a "taste" to it. I'm not sure I want to know what a test would have shown......

2nd January 2007, 16:49	#10 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,453	Re: Compressor humidity indicator To get an ACCURATE correlation you need both the pressure at the time of the measurement AND the temperature of the gas at the measurement point. The former is pretty easy, but the latter is not (accurately.) Without the temperature you cannot correlate the RH to an absolute (mg/m^3) value. Monitoring online does not tell you that you are within dewpoint specs generally (the big risk here is taking a tank filled in the middle of summer, and letting it sit until winter, then diving with it - you could have free condensed water in the tank, and thus have corrosion problems if that's a steel cylinder, or have problems in cold water with a regulator first-stage freeze) What it does tell you is that your dessicant is working and thus your activated carbon is still effective in removing hydrocarbons. That is the point of online monitoring with an "eyeball" - to know that you are still effectively removing contaminents from your product gas. Note that a lot of the "compressor guys" will sell you 20/40% cards. Those are completely worthless as once the 20% one turns your stack is already rubbish and by the time the 40% one turns you're not only pumping water-laden gas but LOTS of oil vapor as well! For those who say "that doesn't work" - yes it does. I've verified my setup with a montoring test and meet OCA (Mod-J) air quality standards just as my indicator card says I need to change the primary filter stack. Most "commercial" shops change the filters and then test for their "certificate." That, of course, is backwards - they should be testing with used filters at maximum life so they see the worst case - not the best case! The shop is concerned with getting sued if they are out of complience. I'm concerned with not blowing up or killing myself while underwater due to contaminated breathing gas. Try diving in the Caribbean sometime if you want to breathe truly foul "air". I just got back from there a week or so and found it basically impossible to find air that didn't have a "taste" to it. I'm not sure I want to know what a test would have shown...... __________________ "A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American." http://www.denninger.net http://www.diversunion.org/liability.htm - Fix the Diving Cert racket
(Offline)