The second one, the deluxe. I believe it was either Iain or swamp that recommended it to me, and I'm more than happy. I found the AE to be on OK low price item, but it leaked down often and I found I could actually tweak open/close pressure much more accurately with the LF although I just left it at the 2000psi that it's set to out of the box. When you hold that thing and really look at the workmansip, you'll never buy an AE priority again. I have a brand new AE priority valve that's been used for maybe three hours that I bought to replace a leaky one that was only about 2 years old. I thought I just had a bad priority, and went and bought a new one. Then I found out that's the m.o. with the AE priorities. Don't get me wrong, they work; but I think most that have bought the LF one are much happier.
Do you pickle your filter media?
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The second one, the deluxe. I believe it was either Iain or swamp that recommended it to me, and I'm more than happy. I found the AE to be on OK low price item, but it leaked down often and I found I could actually tweak open/close pressure much more accurately with the LF although I just left it at the 2000psi that it's set to out of the box. When you hold that thing and really look at the workmansip, you'll never buy an AE priority again. I have a brand new AE priority valve that's been used for maybe three hours that I bought to replace a leaky one that was only about 2 years old. I thought I just had a bad priority, and went and bought a new one. Then I found out that's the m.o. with the AE priorities. Don't get me wrong, they work; but I think most that have bought the LF one are much happier.
swamp diver
Contributor
Agree with Iain's statements above. Now for why.
It matters very much if the purifier reaches ambient pressure after shut down. First off the mol. sieve will not dry out in fact the opposite happens as high ambient humidity is absorbed by the porous zeolite. That is why we store MS in steel paint cans and not plastic storage bottles because moisture will penetrate the plastic and saturate the sieve in very little time.
The other problem with allowing the purifier pressure to drop to ambient pressure is that both the MS and activated charcoal (AC) will release their contaminants back into the surrounding air so on start up you will get a slug of CO2 coming off the MS and a potential slug of all the VOCs that the AC has trapped from the ambient air and the compressor oil volatiles.
I certainly would not want to be the diver breathing off that first tank if filling tank by tank. If filling storage banks you will fortunately dilute down that first slug of contaminants as it is mixed with clean air once the purifier repressurizes. I'd certainly want to check the CO2 concentration in that storage bank though if your system reverts back to ambient pressure every time it is shut down and slug of CO2 is dumped into your banks. In Australia you're only allowed up to 480 ppm of CO2 which is one of the tightest specifications when comparing global compressed air standards.
---------- Post added April 13th, 2014 at 01:48 PM ----------
Have a close look at the first link you posted and compare that to the AE priority valve on your system. Very similar I would say.
---------- Post added April 13th, 2014 at 03:10 PM ----------
Non-return valve = check valve.
The most common source of a leak is the o-ring in the AE check valve shown upstream of your filter. In order to determine if this is leaking close your fill whips and pressurize the purifier up to maximum pressure. Shut the compressor down. Your final coalescor should have zero pressure in it. Back off the inlet fitting to the final coalescor while spraying with soapy water. If that check valve is leaking you will see air escaping at this fitting when there should be none. If leaking rebuild AE check valve (o-ring sizes and type are on AE's web site under technical notes) or purchase a different design of check valve (ball and spring with no o-ring).
If that check valve is ok and you have ensured there are no other fitting leaks on the purifier then it is your AE BPR which is leaking down. Try the LF one instead.
When your system drops down to ambient pressure between compressor runs the moisture in the ambient air enters the purifier cartridge and saturates the molecular sieve. Moisture will even penetrate copper lines if you leave them long enough, and it definitely will penetrate the black thermoplastic lines if left to sit long enough even if filled with dry air. This is why one should run the compressor for a good 20 minutes to ambient before pulling a sample for analysis.
Once you locate the leak then your system will stay pressurized for weeks and you will not have to worry about filling a tank with desorbed CO2 off the molecular sieve.
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OP
Ah ok, I get it now thanks wrt the procedure
WRT to the other, moisture penetrating CU and thermo plastic lines? No, not buying that. If so we'd see a whole lot of weeping plumbing in houses. And even if they did weep, I'd still have a hard time believing that MS can pull a moisture gradient/vacuum to do it much less make any difference to ACR copper or HP thermoplastic with a 7000psi burst rating.
Trace Analytics did tell me to do a 20 min run before I sampled, but that was to make sure the compressor what completely heated up, and pumping properly - ie ring seal vs oil contamination, and to heat up any fill lines greater than 10' left "wide open" to ambient to purge them.
I don't buy the oil logic wrt a RIX which has no oil, but I can understand a need to warm up the entire system - compressor filters, etal and have it pressurized under load before filling or sampling. Everything works better when its warm, me included.
That said, empirical data trumps theory any day of the week, and if it all works better after the first 20 mins, then that's when I'll fill.
WRT 13x, from what I can read, it only regenerates at temp 200-350 degC, not wrt pressure (?). So (trying to understand this) why do you say it will dump its Co2 (or H2O) if at ambient?
Reference: http://blog.restek.com/?p=10617 "13xMS Conditioning"
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swamp diver
Contributor
We have an expression that the 'eyes can't see what the brain doesn't know' which I think applies here.
We are dealing with water vapor (gaseous) in the ppm level not free water leaking through cement wall. Buy it or not if you fill a copper pipe with dry pressurized air at - 60 C atmospheric dew point and then come back six months later there will be an increase in measured water vapor in that pipe. The same goes for thermoplastic except that the water vapor molecules will penetrate even faster if the air in the line is sitting.
Usually this is academic of course unless you are a hospital which is trying to meet a water vapor specification in the compressed air and the copper piping has not been purged for many months. The same goes for a fire hall that wonders why they have failed on the moisture spec when all their piping rather than being stainless steel is thermoplastic. These issues are real and well documented by people who actually work with these problems on a day to day basis.
Please do us a favor and search on here for Iain's guidelines for MS storage wrt moisture penetration. If I recall a plastic ziplock bag is several days, a thick plastic jug is three months, and a steel paint can is 12 months. You can put your 10% humidity disc in each one and see how long the 10% RH sector remains blue. There is a reason LF has an shelf life for its cartridges even if vacuum sealed and unopened.
At pressure more water molecules can be stored in the MS bed and the same goes for volatiles on the AC bed. If you have been running a cartridge for many months and keeping it pressurized but suddenly it loses that pressure the CO2 and VOCs will be released back into the air stream and contaminate your breathing air.
On a smaller scale this will happen with every compressor run if your system leaks back to ambient overnight such that the CO2 retained by the sieve at 3000 psig will no longer be retained and instead will re-enter the air stream. That is why Trace and all the other labs tell you to purge your system for twenty minutes before sampling. Same goes for moisture if the thermoplastic hoses are long and have been sitting for weeks.
If you look in any of the smaller Bauer compressor manuals (where the compressor does leak down to ambient pressure) they all tell the end user to purge the fill lines for several minutes to ambient before filling tanks so as to not end up with this CO2 slug in the first tank.
From the Trace web site:
"The filter will then hold the CO2 along with other removed impurities. If a sudden pressure drop should occur, like when the bleed valve to the purification chamber is opened too quickly or a sudden failure of the pressure maintaining valve occurs, then CO2 and other contaminants can be released into the air stream. Another scenario that can cause high CO2 levels is when a purification filter is not removed but moved up the chain of cartridges to a front position or when it has reached its maximum efficiency. Some filters have a moisture indicator strip on the outside of the cartridge. Even though the strip may not indicate that it is time to be removed, it should not be assumed that the filter is good as new. A filter is like a sponge, it can hold on to unknown quantities of CO2 or gaseous hydrocarbons. When it becomes completely saturated, like a sponge, it will not continue to remove but allow contaminants to simply pass through. If a pressure drop occurs at this point, large amounts of CO2 and/or gaseous hydrocarbons can be released."
Compressed Air Testing - Carbon Dioxide - Trace Analytics, The AirCheck? Lab
OP
Alright Swamp, you make good points that do make sense to me. I might note though that I don't ever remember seeing a CO2 detector on any LDS compressor or even mentioned as something that someone might want to analyze for, like we do with CO, or O2 (Nitrox) & He.
Can I infer from this that a filter dropping its CO2 load just isn't that common? Or perhaps 13x can absorb far more relative Co2 that it can H2O, so in all likelihood, you'll pull your filter because your moisture eye tells you its time, long before the CO2 ever becomes a dumpable issue?
WRT the last, I have the Rix manual, but this is beyond what it talks about....
swamp diver
Contributor
We run a CO2 detector on our nitrox compressor but for different reasons.
Molecular sieve does not remove CO2 from the ambient air rather the outlet concentration is in equilibrium with ambient CO2 so anywhere from 390 ppm to 600 ppm depending on where the intake is located outdoors.
Most breathing air standards have a CO2 limit at 500 ppm (the exception is CGA Grade E which raised the spec to 1000 ppm) so it is very easy to to fail on CO2. The labs don't like their clients failing on the air test so by purging the line beforehand it reduces the chance of failure. As the MS starts to saturate with moisture the water molecule is preferentially absorbed and can 'bump' or roll-up stored CO2 back into the air stream. This slow release of CO2 by incoming moisture will also push the CO2 above ambient levels.
There is no physiological reason to worry about CO2 at 500 ppm rather it is more a proxy marker for moisture contamination. The upper limit of allowable CO2 on the international space station and I believe US subs is 5000 ppm but they try and keep the level below this. If you have a CO2 level in your tank at 500 ppm your maximum exposure at 130 feet will only be 2500 ppm (Grade E is a different story at 5000 ppm).
Here in Canada the CO2 specification has been raised to 600 ppm to reduce the frequency of failures but in Europe many urban fill stations are having to install a sodasorb appliance on the compressor intake in order to keep the CO2 below 500 ppm. Obviously for mixed gas technical diving at deeper depths one should have a lower CO2 concentration.
You can purchase a CO2 detector for $970 from Nuvair but for recreational diving this would be unnecessary if the compressor's intake pulls in outdoor air (rather than indoor air with CO2 from human respiration), the purifier remains pressurized between compressor runs, and the filter cartridge is changed out before the RH exceeds 20%.
Molecular sieve does not remove CO2 from the ambient air rather the outlet concentration is in equilibrium with ambient CO2 so anywhere from 390 ppm to 600 ppm depending on where the intake is located outdoors.
Most breathing air standards have a CO2 limit at 500 ppm (the exception is CGA Grade E which raised the spec to 1000 ppm) so it is very easy to to fail on CO2. The labs don't like their clients failing on the air test so by purging the line beforehand it reduces the chance of failure. As the MS starts to saturate with moisture the water molecule is preferentially absorbed and can 'bump' or roll-up stored CO2 back into the air stream. This slow release of CO2 by incoming moisture will also push the CO2 above ambient levels.
There is no physiological reason to worry about CO2 at 500 ppm rather it is more a proxy marker for moisture contamination. The upper limit of allowable CO2 on the international space station and I believe US subs is 5000 ppm but they try and keep the level below this. If you have a CO2 level in your tank at 500 ppm your maximum exposure at 130 feet will only be 2500 ppm (Grade E is a different story at 5000 ppm).
Here in Canada the CO2 specification has been raised to 600 ppm to reduce the frequency of failures but in Europe many urban fill stations are having to install a sodasorb appliance on the compressor intake in order to keep the CO2 below 500 ppm. Obviously for mixed gas technical diving at deeper depths one should have a lower CO2 concentration.
You can purchase a CO2 detector for $970 from Nuvair but for recreational diving this would be unnecessary if the compressor's intake pulls in outdoor air (rather than indoor air with CO2 from human respiration), the purifier remains pressurized between compressor runs, and the filter cartridge is changed out before the RH exceeds 20%.
clownfishsydney
Contributor
After running my compressor for more than 12 years and over 3,500 fills, I can assure you that the MS does lose moisture to the surrounding filter over time when not pressurised. Even if there was something toxic given off (and there will not be unless there is something wrong with your compressor), this air is, of course, blown out of the system when the compressor starts and the filter is bled. Hence, it does not end up in your tank.
OP
So this is the bottom line right? Change out filters (ie MS) at RH 20%.?
I probably need to call LF since I'm using their carts, but just so I understand what real people are doing in the field based on real testing results....
I found this in the GMC manual: change at 40%RH (which they elude is -50F DP.....)
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swamp diver
Contributor
If you are running catalyst (Hopcalite, Monoxycon, Carulite) which I don't think you are you require air with an atmospheric dew point of at least -50 C to function effectively. That will be achieved at a relative humidity of < 20% if the disc is read at 3000 psi. Also if you are going to be cold water diving (< 5 C/40 F) with high pressure tanks you will want compressed air with a atmospheric dew point < - 53 C (-65 F) in order to prevent free flows.
As for VOCs stored on the AC bed most of the well retained compounds like toluene and ethylbenzene are tightly head up to a RH of about 40% but some of the less well held compounds desorb (re-enter the air stream) well below this. In other words changing out your filters when the RH is 20 percent or less will keep your breathing air VOC-free and optimized for cold water diving.
The fellow to speak with at Lawrence Factor is Mike Casey and he will tell you that the LF humidity strip will change color at 40% RH, however it was never meant to be used on just a one tower system. It was meant to be used in the first tower of a multi-tower train and when the first tower's humidity strip went pink you then changed out all the cartridges downstream at once. The first filter's MS bed would be at 40% RH but the ones downstream would be lower so the actual purifier outlet relative humidity would be approximately at 20 % RH which is where he will tell you a cartridge should be changed out.
Now we all know many operators are using only one LF cartridge so he suggests to change out that cartridge when the first "one-third" of the humidity strip has turned from blue to pink which probably approximates 20% RH. This is probably a reasonable answer to the problem given those cartridge strips are set at 40% RH.
The problem with putting the humidity strip in the cartridge which is better than nothing is that each time one takes the cartridge out of the purifier you are depressurizing the system and need to make sure you flow the whips to ambient for a good five minutes in order to flush out all the contaminants released from the cartridge especially near the end of its service life when the AC and MS beds are near saturation. Much better to take the humidity strip out and put it in an inline eyeball device like you have done.
Just remember that the eyeball in order to be accurate must be read while pressurized. If your system is leaking down to ambient the disc will eventually turn pink much earlier than it should and will not represent the true moisture content of the system. If you want to pass CGA Grade L air (same as fire fighters use) then you will need to switch out your cartridge when the 10% sector has gone pink in order to meet the -65 F atmospheric dew point requirement which by the way Grade E used to require but was dropped in 2004 since so many dive shops were failing on moisture. Every other compressed dew point standard in the developed world though retains the -65 F moisture requirement for compressed diver air in order to protect the efficiency of the chemical filter media, reduce corrosion in steel tanks, minimize bacterial and fungal growth in equipment, and to minimize the risk of cold water free flows.
OP
Thanks Swamp - this has been super helpful and I appreciate your patience in explaining it.
I don't ice dive (no dry suit), though I do use cold water regs for added piece of mind. At worst I'll see low 40s in the quarry teaching (mid next month), but then again that's on the LDSs air (Grade E) so who knows what the moisture content is....
I did have Trace add the moisture tests to my requirement, so I hope to have a fair idea of what comes out of my compressor. That said, its back to figuring out my filter leak ***sigh***
Thanks again mate.
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