Check Valve - Need Help Installing on Alkin W31

[realdiver7]

Pesky.....once I get a feel for how many tanks I can fill before changing filter media, I feel the need to be over-redundant and over-cautious (if there is such a thing with breathing air). I appreciate your input and thanks for the additional data, which is beneficial to know.

 

[rjack321]

There's no pressure level specified. But the RH sensors need to be read "at pressure". If you drain the stack, the indicator the indicator can turn back to blueish.
The same mass of water in an "expanded" volume of gas ends up being a lower RH %age.

rjack, do you have a published source for this or was it calculated independently? I was not aware that CGA grade E specified a pressure level which correllates with the moisture limit. However, the Europeans have dual moisture requirements under EN12201 which depend on final cylinder pressure and but I'm not up to date on this; I wonder about the current specific level specified for 200 bar, eg if they have actually lowered the volumetric humidity to the level of 20 mg/m3 @ 200 bar and 15 mg/m3 @ >200 bar as they were planning to do. These levels would be equivalent to 20% RH at 200 bar and 300 bar respectively at temp of about 24C. Furthermore, the numbers should be equivalent to dew point of about 0 C at the respective pressures. That is the point, really, to restrict condensation in cylinders of high and very high pressure ratings to fairly low ambient temps.

 

[rjack321]

Fire departments who work when air temperatures outside are -20F do not want their regulators freezing up -- the diver underwater is never going to have that occur.

Not exactly. Between abiabatic cooling and the fact that dew point is measured at 1ATA (not tank pressure) you can get 1st stages freezing (both outside and inside) in alot warmer water than you expect. I neither ice dive nor dive in Lake Superior so its not really much of a concern of mine.

 

[pescador775]

BTH just for information -- I also tested my two accumulator filter system after 25 hours of 6CFM compressor run time and was still better than grade E specs.
Jim

Jim, the revised grade E spec for humidity (24 ppm) is similar to the new (proposed?) EN 12021. No way a regulator would freeze using that spec. Many moons ago, divers in the great lakes area were concerned about ice crystals coming from the air supply and the local clubs or shops were backing and filling their filters with extra desiccant, and that was at a time when desiccants were not in widespread use. Also, they were packing the regulator first stages with vaseline. Anyway, your info is very interesting. Any details on hand regarding the amount of dessicant in your tandem filtration system? Any other filtration components upstream of the accumulators such as single or multiple coalescers (moisture separators)? Back pressure valve settings?

 

[pescador775]

There's no pressure level specified. But the RH sensors need to be read "at pressure". If you drain the stack, the indicator the indicator can turn back to blueish.
The same mass of water in an "expanded" volume of gas ends up being a lower RH %age.

Your answer makes sense, I was curious about the particular pressure mentioned in the previous message Of course, the absolute humidity would drop as air pressure falls. That is, the volume of air would increase due to the pressure drop and change the relationship between the fixed amount of vapor and the expanding size of the air bubble. I assume that is what the "RH" sensors indicate unless they can also integrate temp into the output. Personally, I would just specify a temperature range for the sensor and design it to read absolute humidity or use a calibration chart to read RH. I don't know how the Texas strips work but just saying. .

 

[rjack321]

They don't integrate temp at all. They pretty much turn pink upon any exposure to ambient air at all. Since even in AZ heat you have >20% humidity most of the time. I don't exactly know their composition, just like the strips in the LF filters I think.
Humidity Indicator Plugs & Plug Cards, Desiccator Plugs from TexasTechnologies.com
As long as they don't get greasy they are reversible using a hair dryer. Careful trying to reverse one with a heat gun, they do scorch.

Your answer makes sense, I was curious about the particular pressure mentioned in the previous message Of course, the absolute humidity would drop as air pressure falls. That is, the volume of air would increase due to the pressure drop and change the relationship between the fixed amount of vapor and the expanding size of the air bubble. I assume that is what the "RH" sensors indicate unless they can also integrate temp into the output. Personally, I would just specify a temperature range for the sensor and design it to read absolute humidity or use a calibration chart to read RH. I don't know how the Texas strips work but just saying. .

 

[rjack321]

Spy glass indicator for indicator cards
High pressure breathing air compressors, scuba air compressors, Scuba air

 

[pescador775]

They don't integrate temp at all. They pretty much turn pink upon any exposure to ambient air at all. Since even in AZ heat you have >20% humidity most of the time. I don't exactly know their composition, just like the strips in the LF filters I think....As long as they don't get greasy they are reversible using a hair dryer. Careful trying to reverse one with a heat gun, they do scorch.

Hmmm. If the strips surrender some moisture as temperature rises that would be an indication that the strips are temperature compensated and thus give a rough indication of RH as opposed to AH. You see, if one assumes that the atmosphere to which the strip were exposed could vary in temperature and furthermore, assuming that the air contained the same absolute humidity at the varying temps, then the non compensated strip would simply interpret the readings at different temps as the same RH (which would be wrong). However, if the strip gave up water molecules at a more rapid rate at the higher temps then it would chemically record lower absolute humidity at higher temps. This change in perception by the strip at higher temps, eg, that it thinks there is less humidity because it is giving up some water, would give the correct interpretation of lower RH at higher temps even though the same quantity of molecules per volume of air were present. That would be the correct result, eg the RH is lower at higher temps even though the number of molecules per volume of air had not changed in our hypothetical example.

 

[rjack321]

While they can be dried with a hair dryer I'm not sure that has much to do with their sensitivity at realistic compressor temps. 13x can release moisture at high temps as well but for most breathing air compressor installations its not really relevant. I suspect the RH strip reactions are slightly faster in summertime temps, but this may be a function of the air carrying more moisture at filter breakthru time. Too many variables to know for sure.

I do know that these little suckers work. They change within ~30mins of the gas exceeding grade E moisture limits. Like I said before, moisture is the first contaminant to pass the little P0 design filter that Alkins using on the W31. Not wanting to push it and allow the next, more toxic or odorous contaminant to come through, that's when I change my primary filter. Repacking is pretty cheap since it doesn't hold much media.

I did discover that the table in the W31 manual is totally wrong. Alkins stole Bauer filter life data, then substituted filter inlet temp with compressor inlet temp. I wrote to both Airtex and US-CPSC to inform them of the erroneous information. I did not get a satisfactory answer from either. Summertime around here (75F average pumping temp) I get max 11 hrs from the little P0 filter. Winter (average temp ~45F) I get up to 22-24hrs.

 

[pescador775]

I believe it was said that your compressor is equipped with a CO monitor. In that case, and considering that the compressor is electric motor driven, it seems reasonable to omit hopcalite from the stack and just use desiccant and charcoal. This practice might afford some extra filter life if this has not already been done. I don't use hopcalite in the dive locker compressor, but do so with the portables.