Fills dry or in water bath?

[MaxBottomtime]

I always overfill by 2-300 psi, let the tank cool and then overfill again. My tanks typically are overfilled by 1-200 psi when I get in the water. When I had low pressure tanks I used to give them cave fills. They didn't pass hydro their second cycle.

 

[RayfromTX]

You have probably adressed every important point of this issue. Its all about knowing what you are doing. Most tank monkeys do not. By theory the dry process is the best but in reality customer demand rules. I FILL AT HOME WITH A WET TOWEL ON THE TANK. That is a wet fill.

This seems like it would be highly effective if there was a fan blowing on the wet towel. Depending on where you are filling, it may add unwanted humidity to the space.

 

[rddvet]

I always overfill by 2-300 psi, let the tank cool and then overfill again. My tanks typically are overfilled by 1-200 psi when I get in the water. When I had low pressure tanks I used to give them cave fills. They didn't pass hydro their second cycle.

Then I would have seriously questioned the quality of the hydro. "Hydro Dave" is the gold standard of hydroing overfilled tanks as he does a good majority of the tanks in cave country. He could entertain you for a year with stories of tanks not passing hydro at hydro facilities not performing proper tests. This is especially prevalent with hot dipped galvanized tanks. He fails more tanks due to questionable dings and divots on VIP than hydro I believe.

 

[NAM001]

This seems like it would be highly effective if there was a fan blowing on the wet towel. Depending on where you are filling, it may add unwanted humidity to the space.

The issue is heat removal. Moisture removal is taken care of in the mechanical and desicant filtering stacks. Water removes heat what? 20-25 times faster than air. Natural evaporation will do a lot but surely a fan will super charge the effect. I fill in my garage in east texas and he humidity is often 80% and above. we often like to say its 95/95 that is temp and humidity. The point is that you don't necesasarily have to be in a wet bath to get the effect a wet wrap will do nearly the same. The crux of the whole issue is,,,, can you for a business environment afford to have a customer wait 1 hour for a fill with a station that has say 10 whips doing a slow fill and maybe a top off. Especially those stations that say 3000 psi is the limit disregarding the cooling factor. The rule for full lis that pressure that when cooled to 70 degrees at sea level will be working pressure. Most shops have a good idea how much is hot fill psi for the fill rate. A big benefit of a bath is that you can cool the tank to room temp prior to filling. The tank only gets hotter during a fill and if you bring a hot tank from the car that is already at 100+ degrees F. Now complicate that will a compressor that is outside sucking 100+ F air and then heating that up with the compressor. Every station has its own pros and cons. It would be wonderful is all air was pumped inside an A/C space with 40% humidity and the station had 20+ whips.

 

[NAM001]

I always overfill by 2-300 psi, let the tank cool and then overfill again. My tanks typically are overfilled by 1-200 psi when I get in the water. When I had low pressure tanks I used to give them cave fills. They didn't pass hydro their second cycle.

That is very hard to believe, and the 2-300 psi is permitted and not considered to be an over fill by definition. The hitch is that you can do it if you actually calculate the amount of above WP psi that is allowed. So that if you bring a tank in that is 100F it is 30 above basiline temp by 30 degrees. with that you can fill the tank to 3150 and it not be an over fill. 3150 is under the assumption the tank will not heat up from the fill. so minimum fill for an al80 at 100F will be 3150.

 

[MaxBottomtime]

The low pressure tanks were rated to 2400. I used to fill them to 3000 and beyond.

 

[RayfromTX]

The issue is heat removal. Moisture removal is taken care of in the mechanical and desicant filtering stacks. Water removes heat what? 20-25 times faster than air. Natural evaporation will do a lot but surely a fan will super charge the effect. I fill in my garage in east texas and he humidity is often 80% and above. we often like to say its 95/95 that is temp and humidity. The point is that you don't necesasarily have to be in a wet bath to get the effect a wet wrap will do nearly the same. The crux of the whole issue is,,,, can you for a business environment afford to have a customer wait 1 hour for a fill with a station that has say 10 whips doing a slow fill and maybe a top off. Especially those stations that say 3000 psi is the limit disregarding the cooling factor. The rule for full lis that pressure that when cooled to 70 degrees at sea level will be working pressure. Most shops have a good idea how much is hot fill psi for the fill rate. A big benefit of a bath is that you can cool the tank to room temp prior to filling. The tank only gets hotter during a fill and if you bring a hot tank from the car that is already at 100+ degrees F. Now complicate that will a compressor that is outside sucking 100+ F air and then heating that up with the compressor. Every station has its own pros and cons. It would be wonderful is all air was pumped inside an A/C space with 40% humidity and the station had 20+ whips.

I was only talking about moisture being added to the space. Since you fill in your garage(basically outdoors) that isn't an issue. I fill in my house, so it would be. I crank the AC to 71 degrees and my RH is going to be 50%. I have a fan on my compressor to keep head temperatures lower. My filter stacks measure 110 degrees on their surface after several hours of pumping. In my case if I used a wet towel, I would cool the tanks but I would add the moisture to the air in the space.

I know that people like to say that whole 95/95 or 100/100 thing but it isn't even close to right. Yes, it will be 95 degrees and 95% relative humidity on the same day but not at the same time, ever. By the time it is 95 degrees the rh is going to be down around 45%. Regardless that is humid! the wet towel will be more effective in the 45% condition but of course you are probably trying to avoid pumping in the heat of the day.

When you say "you don't necesasarily have to be in a wet bath to get the effect a wet wrap will do nearly the same" that will only be true if the deck is stacked. Factors at play are these. How cool is the water in the tank? Is it circulated? For the wet towel approach it is more complicated. How cool is the water in the towel? Is it renewed as it dries? What is the air temperature and RH? Is there air movement? What is the density and composition of the towel? Those variables make the towel method range in effectiveness from good to almost worthless. For instance, If the towel is allowed to dry out or if you used say an old army blanket, I could see it becoming insulative. With the water bath it is straight up delta T and water movement.

I am not trying to be argumentative. I find the study and discussion of heat and heat transfer mechanisms to be fascinating. Our understanding of what heat even is only occured recently. (late 1800s) Often it is not intuitive. Latent heat and the heat of phase change (evaporation, condensation etc) is highly discounted and is nontrivial. For instance, evaporation requires large amounts of heat which is why it is so effective as a means for cooling. The energy that it takes to raise the temperature of water from room temperature to boiling is only 1/7 of the amount of energy that is required to change that same water that is already at the boiling point, completely to vapor.

You are right, every setup has it's own set of issues. In your case a fan on your wet towel and using a towel with lots of loft or surface area could make it far more effective but only in the drier part of the day. If it is 100% RH then it will do very little and at that point it is more limited to the amount of heat that can be transferred into the limited amount of water(mass) in the towel.

Here is my setup. I am fortunate to be able to top up hours later from my cascade. Point of interest. If my cascade is low and equalizes at say, 3,000 psi and I come back later to top off, the tanks I'm filling will be at 2,700. The cool part(pun intended) is that the bank tank will now be at 3,200 because it had cooled down below ambient from the pressure drop and has how warmed back up. I love this stuff.

Pumping Nitrox - YouTube

• RayfromTX
• Aug 18, 2017

Filling the cascade with 32% while transfilling four scuba tanks

 

[NAM001]

I was only talking about moisture being added to the space. Since you fill in your garage(basically outdoors) that isn't an issue. I fill in my house, so it would be. I crank the AC to 71 degrees and my RH is going to be 50%. I have a fan on my compressor to keep head temperatures lower. My filter stacks measure 110 degrees on their surface after several hours of pumping. In my case if I used a wet towel, I would cool the tanks but I would add the moisture to the air in the space.

I know that people like to say that whole 95/95 or 100/100 thing but it isn't even close to right. Yes, it will be 95 degrees and 95% relative humidity on the same day but not at the same time, ever. By the time it is 95 degrees the rh is going to be down around 45%. Regardless that is humid! the wet towel will be more effective in the 45% condition but of course you are probably trying to avoid pumping in the heat of the day.

When you say "you don't necesasarily have to be in a wet bath to get the effect a wet wrap will do nearly the same" that will only be true if the deck is stacked. Factors at play are these. How cool is the water in the tank? Is it circulated? For the wet towel approach it is more complicated. How cool is the water in the towel? Is it renewed as it dries? What is the air temperature and RH? Is there air movement? What is the density and composition of the towel? Those variables make the towel method range in effectiveness from good to almost worthless. For instance, If the towel is allowed to dry out or if you used say an old army blanket, I could see it becoming insulative. With the water bath it is straight up delta T and water movement.

I am not trying to be argumentative. I find the study and discussion of heat and heat transfer mechanisms to be fascinating. Our understanding of what heat even is only occured recently. (late 1800s) Often it is not intuitive. Latent heat and the heat of phase change (evaporation, condensation etc) is highly discounted and is nontrivial. For instance, evaporation requires large amounts of heat which is why it is so effective as a means for cooling. The energy that it takes to raise the temperature of water from room temperature to boiling is only 1/7 of the amount of energy that is required to change that same water that is already at the boiling point, completely to vapor.

You are right, every setup has it's own set of issues. In your case a fan on your wet towel and using a towel with lots of loft or surface area could make it far more effective but only in the drier part of the day. If it is 100% RH then it will do very little and at that point it is more limited to the amount of heat that can be transferred into the limited amount of water(mass) in the towel.

Here is my setup. I am fortunate to be able to top up hours later from my cascade. Point of interest. If my cascade is low and equalizes at say, 3,000 psi and I come back later to top off, the tanks I'm filling will be at 2,700. The cool part(pun intended) is that the bank tank will now be at 3,200 because it had cooled down below ambient from the pressure drop and has how warmed back up. I love this stuff.

Pumping Nitrox - YouTube

• RayfromTX
• Aug 18, 2017

Filling the cascade with 32% while transfilling four scuba tanks

I dont know where yo are living but here ithe temp and humidity is often both sky high. I can count on one hand the days we have 95 drgrees and less than 50% rh.
Any towel on a tank will cool as long as evaperation occurs and a tank in the 100+ temps from heating during compression will evaperate the wet towels and remove heat, often better than sitting in a wet bath since the heat will leave the tank and not limit the temp drop by sitting in say 80 degree water. . I prefer a bath to put the tanks in but i fill 2 at a time and i have nothing to put them in that has solid walls to hang the tank from. I will soon get a watering trough from a feed store or a metal garbage can.
although you ention the factors of using a wet towel, the end result is that it does cool the tank from fill heat but will not lower the temp below ambient temps. My tanks get very warm filling 2 on a 5 cu ft compressor. I f i had more whips i would do that and fill 4 at a time.
yes i keep wetting the towel as it drys.

 

[Diving Dubai]

Look, wet towels and water baths don't make a real impact on cooling

It's down to simple physics and cross sectional area. The surface area of a Scuba cylinder simply isn't big enough. The walls are thick and store thermal energy, much faster than you can remove it. They are a heat sink. If you fitted them with fins to assist

There's a reason why your car radiator is filled with cooling fins.

Aside from water-baths being lethal in the event of a failure, unless you have the water constantly circulating you get a boundary layer which works as an insulator.

If' you're in a high humidity area, then evaporation is minimal thus the small amounts of cooling are reduced.

Where I live (95F is our autumn and spring temps - the temp doesn't drop that far overnight in the summer) we have properly high temps and because we're on the coast, very high humidity

Cooling is assisted by intercoolers which sit between the compressor and the tank. They get the air down to 5C (-15). The fill room is kept very cold as is the tank storage, and you get a good fill

In a home set up, simply fill the tanks, let them cool over night and top them off. Much easier

 

[RayfromTX]

Diving Dubai
You make valid points. Of course the rate of fill is a factor because the difference that water bath or evaporative cooling does make is greater with time so a short hot fill is hardly worth it. There are however strategies that can be used to make it more effective.

I will point out that if a dense warm object didn’t exchange a significant amount heat in water then we would not need a wetsuit and if evaporative cooling didn’t work in the tropics then we wouldn’t need to strip off our wetsuits once we got back on the boat.