Black dirt coming out of tank?

[vixtor]

Hello,

Yesterday I was washing my tank (it had to stay one day unwashed after the dive). I have rinsed the valve (DIN) with warm water and then purged some air from the tank to dry it. At that moment I have noticed that some black stain was forming on the flat bottom of the DIN valve. The tank is new (I think it was filled ~8 times). I wiped out the dirt with a paper napkin and purged again. The stain formed again. It looked as either a very fine black (100% black, not rust or something else) powder sticking to the still wet inner surface of the valve or it could have even been liquid already (hard to tell).

Anyway, after a few air purges it ceased to apear again. I had the tank visually inspected - everything is shiny inside. The valve has no sign of corrosion. The regulator is also clean inside.

Any ideas what this could have been?

 

[rakkis]

bad air (contaminated with oil from a compressor in need of servicing) ?

 

[vixtor]

I forgot to add that I have dived the tank from 220atm to 40atm with no sign or simptom of any problem. The air felt fine - no smell, no taste.

 

[dannobee]

Could be charcoal from the compressor's filter. Especially if it's a repackable kind and not the disposable cartridge type.

 

[DA Aquamaster]

That would be my guess. Activated charcoal is used in addition to a dessicant to remove impurities. In a hand packed filter the charcoal is usually placed in a nylon and a dacron felt pad is usually placed over the end of the cannister to contain any dust that might otherwise come loose and follow the air into the fill whip. A spring is also used to keep the charcoal compressed to prevent it from ziggling in the filter and breaking down into dust in the first place.

Any significant degree of carbon showing up on the valve or in the filter usually indicates the filter elements are either breaking down or it is improperly packed.

Very small amounts of carbon are common and many regs that come in for annual service show traces of carbon on the HP seat.

Put a white piece of cloth over the tank valve opening, open the valve slightly and run some air through the cloth for a few seconds at a moderate flow rate. If you have carbon, rust, aluminum oxide or oil in the tank, it will usually show up on the cloth as a black, brown, grey or yellowish stain on the cloth.

 

[vixtor]

I have thought about this and tried to put a paper towel on the valve and let some air to pass (even at a higher than moderate flow rate), in various positions (valve up, valve down, horizontal and so on). The paper remained clean, but I did this test only after the valve was also not getting dirty anymore (not immediately after I have observed the issue).

Indeed, it could have been charcoal (I was tempted myself to compare it to graphite both in color and in the traces left on paper when wiping out the valve).

Considering that both the tank and regulator were considered clean at inspection, is there anything else that I should do? Is there any big risk from inhaling charcoal dust in the lungs? I think I am inhaling more common dust every day by living in a big city than the charcoal dust from the tank anyway.

I am thinking about trying to fill the tank again at all three compressors that filled this tank until now, and see if after any of the fills I will be able to find again some black dust when opening the valve.

 

[dannobee]

I am thinking about trying to fill the tank again at all three compressors that filled this tank until now, and see if after any of the fills I will be able to find again some black dust when opening the valve.

If you have access to the compressors, it's likely that the end of the fill whip will have residue from the charcoal. A quick wipe with toilet paper on the DIN fill whip should identify which compressor has the problem.

Obviously nothing extra in your lungs is better than breathing other stuff, but activated charcoal isn't as bad as some other things that a compressor could spit into your tank. Like you said, breathing city air has a lot of crap in it.

 

[DA Aquamaster]

Yes, I will never adjust to the general smell and taste of the air in the DC area - really crappy - after living somewhere where the air is actually clean.

I agree a visual inspection of the fill whips would probably indicate the faulty filter, and if not the white cloth test probably would.

 

[muddiver]

Charcoal in the lungs is a bad thing. Coal miners in the south east of the U.S. (and other parts of the world) use to get what is called "Black Lung". You might as well just smoke a pack an hour of unfiltered cigarettes. I suspect that the first stage regulator filter and inner working will capture most of the powder but you can never be to careful with your lung because usually what goes in does not come back out.