Vacuum pump to dry inside of tank? Refrigeration people?

[spoolin01]

Any amount of vacuum would accelerate the evaporation - and there are cheap ways of making at least some vacuum - but vacuum without a moisture trap of some sort won't remove the humid air very quickly since there's no flushing. Maybe you could alternate vacuum with ambient air. As cited, simple air circulation will drive it off quickly, and a little heat will of course make that go even faster.

 

[NAM001]

after i get my tanks where i think thery are dry i fill to 500-1000# and then vent them empty a couple of times. this should remove the moisture residue in the air. as long as your compressor has good dry air this should do the trick after you get it blow dried.

 

[Doc Harry]

I got some rigid brake line from an auto shop and attached it to a blower nozzle (all degreased and thoroughly cleaned, of course). I put a little bend in the end of the brake line to facilitate blowing water out of the cylinders.

Hooke the nozzle up to your BC inflator hose, stick it into your cylinder, and blow your tank dry in 60 seconds.

 

[mvidos]

In HVAC we use also Nitrogen through pipes if we need to weld joints. Nitrogen pushes out air and there is no oxidation. I have just found out Nitrogen can not hold humid. I would vacuum tanks with HVAC vacuum pump and I would possibly fill and flush/vacuum again with Nitrogen. If I would have tanks sitting over winter or other I would probably leave nitrogen inside. Nitrogen is inexpensive and inert , and can not hold vapore… so sounds perfect

 

[Still Kicking]

In HVAC we use also Nitrogen through pipes if we need to weld joints. Nitrogen pushes out air and there is no oxidation. I have just found out Nitrogen can not hold humid. I would vacuum tanks with HVAC vacuum pump and I would possibly fill and flush/vacuum again with Nitrogen. If I would have tanks sitting over winter or other I would probably leave nitrogen inside. Nitrogen is inexpensive and inert , and can not hold vapore… so sounds perfect

Until you forget you put N2 in there and go diving....

Non-breathing gas in breathing tanks is a very bad idea. I know, you'll label them and how could you possibly forget but it happens....you pass on and a friend/neighbor/relative takes up scuba......

 

[Tracy]

Yes, it works fine. I use it to dry large ASME tanks when I am installing them. They tend to sit unsealed for long periods of time.
Without a micro gauge, you are wasting your time as you won't really have any idea when the moisture is gone.

 

[Waterwulf]

Why not warm the tank to evaporate the moisture? Water boils at 212 degrees but that wouldn't have any effect on the metal of the tank.

 

[spoolin01]

... I have just found out Nitrogen can not hold humid....

This seemed surprising so I poked around a bit - there seems to be enthusiasm in HVAC and some other areas for making a big deal out of the semantic point that gases like N2 or air are not literally "holding" water vapor - in the sense of inter-molecular attraction I suppose - it's just sitting there in the mix like another gas. I guess that's something of an analog to the "ha ha - oxygen tank - ha ha" scuba meme. I don't think there's much difference if any in the vapor pressure profiles between 100% N2 and air.

 

[lucca brassi]

vacuum helps to evaporate water , but you still needs some water absorber inside tank ( even HAVAC have it ) like zeolite or silica

 

[mlavigne]

This seemed surprising so I poked around a bit - there seems to be enthusiasm in HVAC and some other areas for making a big deal out of the semantic point that gases like N2 or air are not literally "holding" water vapor - in the sense of inter-molecular attraction I suppose - it's just sitting there in the mix like another gas. I guess that's something of an analog to the "ha ha - oxygen tank - ha ha" scuba meme. I don't think there's much difference if any in the vapor pressure profiles between 100% N2 and air.

I think the (oversimplified to the point of being wrong) thought process here is that high-pressure tanks of N2 are low humidity, just like high-pressure tanks of air are low humidity to prevent the vapor from condensing in the tanks. N2 will still "hold" water vapor, as will a vacuum (well, i guess it wouldn't be a vacuum anymore...).

In HVAC, the system is typically prepurged with dry (bottled) N2 to do most of the drying, and then the vacuum process (typically to <500 microns of pressure... 500 um of Hg, i think...) will get the last bit. Even in HVAC, if its taking too long to vacuum (too much water in the system), its often easier to re-pressurize with more dry (bottled) N2 to flush more of the vapor out and then re-vacuum (the pumps move more mass flow rate at lower vacuums, so you are sweeping more gas faster with these purge-vacuum cycles than vacuum alone).

The only benefit of the HVAC method vs normal scuba tank dry-air would be the lack of O2, which may slightly prevent surface rusting while drying. You can also heat the tank to speed things along (also done in HVAC).

@lucca brassi - those absorbers should be completely dry on installation- those are to grab any moister due to minor leaks as water likes to get in the oil and make fun organic acids that motors love.

YMMV.