Portable compressors / air quality ?

[Mverick]

Hello,
Please email me at mverick160@aol.com. I have some questions about the filter assemblies for the mil surplus compressors.

I have 2 of them. One with a 3hp 220 motor. With a water condensor. It will go to 4500psi. No problem. But I haven't used it for scuba yet since I don't have a filter. I use it for my Pellet guns. I bought it finished from a guy. He builds them for Pellet gun use.

One with a 5hp Briggs OHV motor. It's not put together yet. I want it to take on lake trips with me.

Basicly I need to know what type of filter assembly and where to get one. Also where to get the hose too...

And you're right. The compressors are little. Mine are both the 4cfm models. They don't weigh more than 10lbs for the pump. The motor weighs more than the pump.

 

[zboss]

So - where would one find a surplus military air compressor suitable for scuba use? I have need of one in the British Virgin Islands but can ship from mainland USA.

 

[pescador775]

Maybe I didn't make it clear. So, to repeat in short form: try E Bay or protecair.com or airtimeair.com, or plansandkits.com Protec sells on EBay as 'insanelyjane'. Ask for Scott and say 'Dennis sent me'.

 

[oxyhacker]

A few comments on small compressors:

- The little Coltri (which is what a MaxAir 35 is, an Italian Coltri MCH6, and, incidently available for about $800 less from others suppliers as other have pointed out here) has a very small filter cartridge, and while both MaxAir and Lawrence Factor, who makes the cartidges, says it will deliver grade E air, it doesn't do so for long and doesn't take much neglect (like forgetting to drain the separator, which must be done every 15 minutes or so, just once) to knock the filter out, at which point the compressor wil start delivering dangerously contaminated air. Extra filtration is a real good idea with these machines.

- Extra filtration doesn't have to be expensive if you don't mind hand packing (which is much cheaper too) - it's often possible to find a used stack from a slightly larger machine, or even make one from SS pipe or a surplus hydraulic accumulator (which I notice some of the vendors of surplus compressors are also doing). You don't want to get carried away with size since little compressors like the Coltri aren't rated for continuous use, so you won't be pumping all that much air anyhow, and a large filter will take forever to pressurize.

- the little Bauer or Poseidon (they are the same) are much better rigs for only a bit more money, and have larger filters.

- If you are thinking about a surplus compressor, like the South Wind/Kiddes currently turning up on Ebay, grill the vendor about long term parts availability, or buy it with the understanding that it will be a throw-away machine. A lot of these were made years ago to military contract, and have no civilian equivilent or current source of parts. The vendor may have gotten an inventory of surplus parts with them, or just the compressors and may be cannabalizing some machines to get parts for others, in which case the parts most in demand will quickly become unavailable.

- flash point isn't the only factor in CO production. All oil lubed compressors produce carbon to one degree or another, and carbon can start smoldering at as little as 500-700 degrees.

- Hopcalite is not a complete answer to CO. According to Lawrence Factor, the hopcalite in an average filter (and the little Coltri/Maxair filters are considerably smaller than average!) can handle only 300 ppm CO or so, which is much less than the lethal threshold. Take Pescador's advice and add a remote intake!

- Pescador says that water is the main contaminant and that we are overreacting. True, but it's water mixed with oil - the oil is the real problem but once the water wipes out the filter the oil starts getting in the air. Wet sump piston compressors are all inherently filthy, since some oil by design always gets past the rings. Inhaled oil can cause an irreversible and sometimes fatal condition caused lypoid pneumonia where the lungs become coated and function is impaired. Too much water in the system will saturate the filter, at which point it will no longer remove the oil. That's why good filtration is absolutely essential. Did someone mention asbestos? Inhaled oil is every bit as bad, and synthetic and even food grade oils are equally bad (in fact the diester synthetics may even be worse). It's likely that many users of older compressors from the days when just carbon was used in the filters suffer from LP to one degree or another.

BTW re power loss on small engines at altitude this is often due as much to carburetor mix as to the effects of the thinner air -the thinner air in effect richens the mix, so the engine is no longer in tune and doesn't run as well. Since most small engines have carbs with adjustable needle jets they can easily be retuned for altitude.

 

[Genesis]

A Rix?

 

[pescador775]

NO, RIX is not the answer. Those expensive things eat piston rings and need rebuilding too often. Buy a RIX for pumping pure oxygen, otherwise, you're better off with an oil lubricated compressor.

Hacker gives some good points but he veers off into wild statements such as compressor oil is 'as bad as asbestos'. This is nonsense. Drinking a powerful diester oil will give you diarhea, so don't do it. It won't kill you however. You see, I started off by kidding divers about the fear factor and that's what we've come down to.

In contrast, fearless Bauer Co's compressors use a positive crankcase ventilation system. A small tube vents crankcase oil vapor back into the first stage of the compressor. Most dive pubs were horrified by this back in the 70's when this change was introduced but Bauer engineers know what they are doing.

Virtually all of the surplus compressors use large condensators manufactured by Walter Kidde or Stewart Warner. The manual for the US Navy divers' Stewart Warner compressor says that the condensator must be drained at least "every two hours". If you can't adhere to this minimum requirement you should let somebody else fill your tanks. Best practice is to drain after every tank fill. In any event, condensators remove most of the oil with the water. The rest is removed by the final filter. The resulting air is perfectly healthful to breath, even if a little dry to the taste. Yes, as 'hacker' says, oil and water form an emulsion and this is what the condensator removes through a drain. If you see any water in your tank there is also possibly some trace oil, just a TRACE. Since the SCUBA tank itself acts like a condensor, it holds the majority of any deposits of water and oil as a liquid, and even in this extreme example mostly does not enter the breathing air in any but extremely tiny amounts. You know what to do, have your tank cleaned and check your air source, whatever it may be. As long as your oil lubed compressor has a good condensator and fresh filter you could breath from this source for 20 years and get about the same total toxicity as smoking one cigarette. However, if you pump exhaust fumes all bets are off. Bingo, 1,000,000 cigarettes. Same for RIX, by the way, and worse since some of these don't even use a final filter.

Why are you people so willing to believe anything negative? Look at it this way, buy a compressor, use it, feign a headache and seek a lawyer. Tell him Omar sent you.

Pesky

 

[pescador775]

The main improvement to the final filter has been the development of 'molecular sieves' like Vaporshell 13X. This does knock out residual humidity and oil in the air supply. The other improvement to air quality management is not obvious to anybody but a compressor engineer or tinkerer, like me. This involves the use of micronic filters in the separator. These started out as 'air stones' and later, stainless steel elements. Either one is designed to a five micron mesh. However, they don't really filter as one might imagine. They are 'labyrnthine' devices with cause humidity to coalesce into water. They do this by increasing effective surface area and are a huge improvement over the old nozzle type devices.

Oh yes, CO...how well does hopcalite work? Hopcalite, a mixture of manganese oxide/copper oxide with some doping compounds, is an effective catalyst. It's effective up to 300ppm using a short tower of the stuff. Atmospheric CO ranges from 1-50 ppm depending on where you are. One would think that the small amount of expensive hoppy which is contained in a typical filter would be sufficient. However, one must consider that the effective concentration of CO at 200 bar is 200-10,000ppm, or up to one percent CO when it meets the hoppy. This is way beyond 300 ppm. One wonders why even bother. Fortunately, the effective level of CO when breathing underwater will only range from about 2-500 ppm (worst case, 300 foot dive). Did I say 'fortunate'? This is one good reason to not fill tanks in an exhaust stream or near the freeway! Seriously, we're always breathing a bit of CO and the concern to tank fillers is to use common sense and a bit of advice. If you are using your portable at sea where you both belong, keep the intake away from exhaust. If the boat is underway keep an eye out for boat exhaust being suck back over the transom. If you're home, don't fill at rush hour.
Pesky

 

[pescador775]

It's all relative. The question should be is compressor oil too hazardous for use in breathing air compressors. I bring this subject up because of the bad rap that synthetic oils are getting from the purveyors of 'food grade oil', namely UBS of DNAX fame. Also, similar remarks from 'hacker'.

Firstly, every drum of compressor oil is accompanied by a 'hazard' sheet as required by law for chemical shipments. Nowhere on this sheet is mentioned any problem with pneumonia or cancer. There has been no such finding by the DOT or EPA. Secondly, with the current climate of litigation, no compressor maker would touch these oils if there was any hint of health risk when used as intended.

Let's look at a severe case situation where the compressor is operated without a final filter. In this way, some moisture and oil vapor would enter the SCUBA tank. What does this mean for the divers' air supply? Right away, one will notice that the air from the tank valve has a funky odor, the smell of oil. A test done on the air supply will show that the humidity is higher than normal (higher than -40 dewpoint) but the oil vapor is so low as to be difficult to measure. Why is this? Understand that water is much more volatile than oil. The boiling and evaporation points for water are much lower than oil. This means that water will not only collect on the walls of the tank but form a gas called 'humidity'. This gas will travel with the air stream to the diver. However, the (much smaller) amount of oil collecting on the tank wall is non volatile and will mostly lay on the walls of a tank without evaporating. A few molecules of the oil will evaporate, however. This is what causes the odor. The human nose and particularly, the taste buds, can detect incredibly small concentrations of a foreign substance like oil, just a few molecules per liter of air.

With a final filter, the small amount of oil vapor coming from the compressor's separator is trapped, at least enough is trapped that it cannot be subsequently be detected by the divers' senses. That is 'grade E' air for the layman, and is not hazardous in any way.

 

[Uncle Pug]

It is a shame to see you carrying on a conversation with yourself here is this thread... seems like everyone else left the room.

Anyway... I surmise from your posts that you are not a layman... though from your profile I cannot see just what kind of expert you are I can tell that you must be an authority in this (as well as many other fields no doubt)... correct?

So perhaps you can help me out here since you also seem to be an expert in RIX compressors.

I have a RIX SA-6B that I feed O2 to so that I can continuously blend EAN32.

How many hours can I expect a set of rings to last?

 

[pescador775]

Depends, they seem to last about half as long as a comparable oil lubricated compressor. Fortunately, the RIX is designed to allow routine replacement of the rings.

I think the people who need to see my remarks are around.