Air fill question:

[FIXXERVI6]

Even with your RIX?

I've never bothered storing the water needed. Slow is my preference, but practicality plays it's role, case by case. I've made many hot fills that will cool more than a few hundred psi. which is estimated to balance out. To me, water is for IN/OUT operations like you'd see in Florida.

My preference is dry, nice and slow... exceptionally slower w/ high O2 - & keep your tanks & valves 02 clean

nah the RIX goes slow enough its not an issue, I'm talking more about the "quick get me back up to 3600 before little river closes" type fills

 

[FIXXERVI6]

The last I heard his RIX was sick...

yea but I'm 95% sure I'm going to repair it at this point, even if I turn around and upgrade to a bigger one later down the road repairing the rix will allow me to get more money out of it, easier to sell a working compressor than one that needs work.

 

[Dark Eternal]

Personally the wet fills seem to make a difference to me. I got a fill on my 108s to 3600 when they were sitting in very cold (as in ice in it) water. Jumped into the 68* spring and watched the guage climb to 4k as they warmed up in a matter of a minute or so.

 

[GrumpyOldGuy]

An interesting tidbit, I have found several tank o-ring leaks in the fill tank. The leaks were slow enough not to be noticed while diving. The caveat of course if the tank filler needs to have an IQ above room temperature to keep water out of the valve.

 

[FIXXERVI6]

plust there is always the added benefit of watching a shower of water when a burst disk lets go in a water bath, always fun!

 

[ScottUgly]

Found two articles suggesting that wet is not the way to go.

http://www.fillexpress.com/library/dryfills.pdf

http://www.fillexpress.com/library/wetfills.pdf

 

[Thalassamania]

Those two references, the first by Fred Calhoun (a P.E. and NAUI Course Director) and Bill High (of the NOAA Diving Program and founder of PSI) are worth reading. I will copy part what Bill said here:

What about the perceived benefit that the water bath will absorb explosive energy? There simply is not enough water between the FSO and the exploding cylinder to have any
measurable effect whatsoever unless of course the tub is a nearby swimming pool. But, surely the tub itself will provide protection. Not true when you look at a great many of the
water tubs in use today. Plastic garbage cans are used as well as sheet metal buckets of one sort or another. The energy within a full, exploding cylinder is so great, well over one million
ft. lbs of potential kinetic energy, that all these containers break up and contribute shrapnel to injury and property damage. Even concrete block barriers usually disintegrate.​

 

[richerso]

Those two references, the first by Fred Calhoun (a P.E. and NAUI Course Director) and Bill High (of the NOAA Diving Program and founder of PSI) are worth reading. I will copy part what Bill said here:

What about the perceived benefit that the water bath will absorb explosive energy? There simply is not enough water between the FSO and the exploding cylinder to have any
measurable effect whatsoever unless of course the tub is a nearby swimming pool. But, surely the tub itself will provide protection. Not true when you look at a great many of the
water tubs in use today. Plastic garbage cans are used as well as sheet metal buckets of one sort or another. The energy within a full, exploding cylinder is so great, well over one million
ft. lbs of potential kinetic energy, that all these containers break up and contribute shrapnel to injury and property damage. Even concrete block barriers usually disintegrate.​

All of the above assume that a cylinder behaves (explodes) as a bomb casing. Cylinders rupture. They do not explode. Energy released through the rupture occurs at much slower rate (hundreds of milliseconds vs. 3 milliseconds or less). All the rupture will do is blow water around the room. Most water vessels I have seen simply are not strong enough to form a secondary explosion vessel. The water vessels tend to be thin plastic or sheet metal as you have noted. This material will simply rip if it even reacts that much. Most of the time, the escaping gas from the cylinder will simply blow water around and then vent to the top (assuming the water vessel is customarily loaded from the top with cylinders and is customarily open to ambient).

Having said all of this, there is a possibility that a chunk of the cylinder material could separate and become flying shrapnel that penetrates the water vessel and continues toward people; but then again this is a possibility if you stand the cylinder upright in the room. Hence, the water in a tank does serve the function of viscously absorbing some of that kinetic energy. I am not saying it absorbs all of the energy. I am not saying water tanks make the process safe. I am saying water tanks make the process safer than not having a water tank.

But even the possiblity of a piece of cylinder material separating and becoming shrapnel should not be possible if the tank material is correctly selected and heat treated. It has something to do with ductile fractures vs. brittle fractures.

 

[Thalassamania]

Actually, the scenarios that Bill describes have no assumptions, they stem from empirical tests in which rusted steel cylinders were pressurized to failure and the results observed.

 

[PvilleStang]

Actually, the scenarios that Bill describes have no assumptions, they stem from empirical tests in which rusted steel cylinders were pressurized to failure and the results observed.

Pretty sure the assumption is that the burst disk remains intact while the cylinder fills to around 10,000 PSI. Most tanks fail well beyond the 5/3 working pressure threshhold. Take into consideration that most fill stations won't get anywhere near that pressure, and now take into consideration that there are several failure points in each of the different tank types. Blowing off valves are likely, which in fact is quite dangerous (thus the VIP test on the threads on AL tanks annually). Someone show me a statistic of the number of air fills vs. number of failures and I'll start to listen to the failure arguments.

Hey, you shouldn't live within 5 miles of anyone, because the odds of a gun discharging into the air and hitting you are way too high!