Scalding hot tanks

[Colliam7]

I was driven there by a friend, who commented he had not seen tanks filled before out of the water.

For future reference your friend apparently has VERY limited experience. Some would just say your friend is ignorant, but I won't use that term as it may be offensive (even if I think it applies). The majority of scuba cylinders are filled 'out of the water'.

Another diver had just walked out of the store after his first visit, and commented there was no way they filled them without being in the water. He then felt the tank, and said, yup, filled out of the water. He said he would not have his tanks filled here.

LOL. It is certainly the prerogative of that diver to take that position. I suspect he also has very limited experience. And, I would not necessarily follow his lead on the subject. The challenge here is very much like the issues with the Internet in general. Absurd comments are made, and somehow become accepted as fact. You could do the same with mine, if you wish, although i suspect mine are factual.

]Is it normal to give them back very very hot? Is it normal to fill them without cooling in water?

No, and Yes. But, in reality, it depends. I have received filled cylinders on many occasions that were quite hot to the touch - I was traveling, I needed a quick fill at a local fill site, and they were hot when I took them. I didn't have time for cooling them in water. I have also filled cylinders for customers, and myself, where time was limited, and I just needed 'most of the rated capacity', and the cylinders were hot when given back to the customer. Ordinarily, what we will do is fill the cylinder, take it outside and place it in a fresh water bath to let it cool for a few minutes, then bring it back in and finish filling back to, or slightly above, the rated service pressure. Where the customer doesn't pick the cylinder up for several days, the cylinder temperature returns to ambient over that period (as heat dissipates from the metal into the atmosphere), so it doesn't feel hot. Getting water in the cylinder? Please. If you open the valve and blow air (and residual water) out of the aperture, if you take a paper towel and wipe the valve aperture, ETC. you will not inject any significant amount of water. More water would be injected if the fill air is humid and not filtered.

As for concerns about the fresh rinse water being contaminated with salt water with repeated use, yes that can happen. Most competent fill operators drain and refill water baths each day, if there are salt water-immersed cylinders being brought in. We are an inland shop, where most of the cylinders will have been in fresh quarry water. Nonetheless, we refresh at least every other day.

A fill station that puts bleach in their water rinse bath and doesn't bother to mention it to their customers - twits. Customers who don't bother to ask - . . .

 

[Shasta_man]

<<Even after just 18 dives>> you are letting your ego get WAY beyond your skills. Hopefully the next post about you isn't made by DandyDon (he posts incidents from around the world if you didn't know). THe diff from his usual posts will be we will already know what the problem was.

How did you go from "gee sirs, are hot tanks a problem?" to "I don't need no damn safety or visibility, I can outdive all of you!'"? And since explosive force is directional, make sure you are standing where that protected spot you mention is, not the open part. And an explosion in a confined space will be fun...but we don't need no stinkin' safety.

 

[g1138]

As far as safety I would say a tank in water is more safe. Water may not compress much, but just like lead plates, it can slow down shrapnel.
I know this because I am a physical chemist, not because I am an old time diver

Right, but it's not the tanks that will shrapnel. It's the water trough, 5mm's of steel or plastic container that you're housing all that junk in.
That stuff is propelling through air with water right behind it.

The tanks will peel away nice and "cleanly". You are just left with a tank with one big crack or peeled hole in the wall.




If you want to have protection against a tank failure during fill, they make that too. They're called blast chambers.
And they don't use water.
You are safer using an empty steel trough than a water filled trough, because once again. Water doesn't compress, air does, and Air pushing against the inside of a trough will distort it way less than water.

Why do you think they use depth charges against submarines instead of balloons?
Why do you think dynamite fishing is so effective?

 

[GrandpaScuba]

Filling in water is an antiquated process for all the reasons given by g1138. All the local stores, in our area, that are professionally run, have removed their water tanks.

 

[String]

The only conceivable advantage in water is if you have a pumped/radiation cooling system. That will allow you to fill *slightly* faster for less overall heating. The difference is absolutely negligible though which is why nobody does it.

 

[j yaeger]

...it's far more fun to watch a burst disc go in a water bath...

 

[DogDiver]

...it's far more fun to watch a burst disc go in a water bath...

Burst disc??????? What are those????? Could start a whole new thread on double and triple disc.


Sent from my iPhone using Tapatalk

 

[g1138]

The first thing I had to disregard after my scuba class was safety. All the never dive alone, buddy system stuff went out the window, and was saved for a diving holiday. I think this has made me a bit better of a diver. There is no one to catch my mistake, or pick me up when I fall. Even after just 18 dives, I know my gear very well, and I am confident in skills most people never even master. EG I can dive in a body of water with no visibility at all. At times it is so bad I see the reflection in my goggles. I can mostly see things less then 3" in front of my face. The best visibility I have ever had while working, was 3' one day. I am not saying I am ready to cave dive, decompression dive, ECT. What I am saying I have learned a lot of advanced diving, within the first week. I think I also dive much more then the average person, at least once per week. So safety? I have enough safety, and all that I need to dive to 12-16' solo, weekly, in 0 visibility.

I read your blog. You dive in a 15ft harbor cleaning boats. You move with your hands on a hull, if you make a mistake in bouyancy or position you go to the solid bottom or 3 ft to the surface. That is neither advanced or skillful.
Real commercial boat cleaning operations will use powertools, zinc blocks, drills, and 1000lbslift bags for salvage.

If you die under a boat with your plunger and scrubby pad you will be a laughing stock. That's how "advanced" you're touting to be.
There is nothing advanced about maintaining a hold onto a boat that's bottom reaches 5-10feet below the surface. Viz or no viz.
There is minimal risk in your dive operation, which gives you the perception that you have enough safety. You aren't facing many safety issues to begin with other than keeping the engines off and breathing.
Students in an 8ft pool doing BC ditch, surface, and recoveries face more safety issues than that.


You need to suck up and listen to us. Many of us here understand what it is like passing the Basic OW course with flying colors; which I assume you did. Those of us felt superb and competent, but looking back it is the same for all of us in that position. There was a lot that we did not know, and even more that we didn't even know there was to know.

 

[NAM001]

There is a lot of feelings on both sides of the issue. You put the tank in water to remove heat. Technically you should not have a need to do that. The heat build up is a physical symptom of filling too fast. If you think the out side is hot then you should feel the inside. (If it were possible). The outside has only the heat that has made it through the walls of the tank. An AL80 is say 1/2 inch thick. That means the inside is expanding faster than the outside of the tank. Filling slower is the key to low heat generation. Keep in mind that the AL tanks are tempered at I think 180 f. The outside temp is no indication of the inside temps. Can anyone say neck cracks. Steel is much more forgiving.

On the prowater side of things. A tank that is put in water with fill hose put on first can be cooled from the temps from outside air prior to starting the fill. You are never going to get a good fill depending on who you ask when you bring a 100 f tank in for a fill and they jam it in 2 min to 3000 psi and 150 f and you hit the 75 f water. Thats a 75 f drop in temp and about 400+ psi drop. I have always filled in water or with a wet towel on the tank to remove the heat. There are shops that fill in AC rooms. so the room and water tank is 70 f or in the neighbor hood of that. Working pressure is the pressure that is allowed to be filled to at i think 70 f. There are those that belief that ie 3000 can not be exceeded on a fill. 3000psi on a 100 degree F tank is an underfill cause it is not 3000 psi at 70 f. So you cool the tank first to 70 then fill as oppose to filling and coolinig to remove the fast fill heat.

If you are not going to top off the tank to make up for the cooling when it cools, then there is no real need to wet fill.

There are other ways to accomplish the fill generated heat and that is to cool the air before you put it in your tank. Many compressors have water heat exchangers on the final output to cool the air for the purpose of improving filtration precesses. What is attempted by those who do wet fill would be partially fixed if you were filling your tank with say 50 F air and not 100+ F air. All these options would be better than thinking your inside tank is staying cool in water based on outside temperature.

Fill stations outside in hot temps are the worse for getting a good fill. Especially if you are filing from he compressor. Banked gas is much better to fill with as the gas has already cooled to surrounding temps. I have seen fill units that have piped a cooling coil in a ice bath in line with the fill whip. Still all in all a nice slow fill is te way to go.so long as you can do it. By that i mean , Dont even expect to have a cool tank if you are filling your tank directly off a 6-10 cu ft compressor. Its not going to happen. Shops are not going to give you a slow fill at the expence of not being able to use that whip time on other tanks. Why do a slow 20 minute fill when you can do 10 x 2 minute fills and make 10 x more money. I have found that when enting tanks I am often told that for those who check any tank with greater than 26-2700 is considered a full tank.

So I waited today while the dive shop filled my tanks. I was driven there by a friend, who commented he had not seen tanks filled before out of the water. I said, wow, these are hot. Another diver had just walked out of the store after his first visit, and commented there was no way they filled them without being in the water. He then felt the tank, and said, yup, filled out of the water. He said he would not have his tanks filled here.

Being newer to this sport/occupation I was unsure, as I had never waited before for my tanks while being filled. Is it normal to give them back very very hot? Is it normal to fill them without cooling in water?

 

[spectrum]

I think the folks that had good luck filling wet were also filling gently (self included) and taken as a whole had good results as long as they handled things to prevent the introduction of water.

A fast fill will be a bad fill any fill short of one taking hours will result in heat and a post fill pressure reduction. Even at 300 PSI / minute you can expect a 200-300 PSI pressure drop. That means having the pressure creep up over 8-10 minutes.

Forgive me if it was mentioned in an interim post but the insulating properties of air are often ignored. Molecules of air enter the tank and get to expand as they enter a lower pressure space. They are doing the happy dance. As the pressure rises they get more and more crowded and like a crowded bar room friction is generated and things get hot. Once this happens you have a body of hot air. Just as we insulate our homes or dry suits with stagnant air the air in the cylinder is not in a big hurry to conduct air to the cylinder wall which can dissipate it. Since we don't have a circulating fan in the cylinder to promote the heat exchange it can take about 4 hours for the whole thing to reach ambient temperature to allow for a meaningful pressure check.

When you consider what is going on in the cylinder you can start to see how limited the effect of a cooling bath is.

Pete