Shops in the area that fill using a water bath

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winte.r
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Re: Shops in the area that fill using a water bath

Post by winte.r » Sat Oct 19, 2013 9:06 pm

My dive shop fills them from the bank, dunks them in the water for a while and then tops them off dry again. I don't think that at the temperatures involved that thermal cycling is an issue for steel but I wouldn't want them to do it with an aluminum tank because of its much higher thermal conductivity (although offset by higher specific heat) and lack of fatigue limit.

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Re: Shops in the area that fill using a water bath

Post by BASSMAN » Thu Oct 17, 2013 10:27 pm

Put my tanks in a bath, pump them up to 4,000 psi and I have a 15 minute fill with nearly 3500 psi when I hit the water! And that's all I have to say about this! :neener:
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Re: Shops in the area that fill using a water bath

Post by Mateo1147 » Thu Oct 17, 2013 9:06 pm

Mateo1147 wrote:The slower the fill rate the less heat generated. Wasn't it the master on Kung Fu that always told Grasshopper to have patience?


[/quote]Not exactly. There's the same amount of heat of compression going to 500 to 3000 psi in 3 minutes vs. 20 mins (in joules or whatever unit you want to measure in). That heat just has more time to dissipate during the 20 min fill so that at the end of your fill time the gas isn't as hot. Hence the lower pressure drop upon cooling from the slow fill. Same total heat generated just more heat was lost in the extra 17mins of fill time.[/quote]


You are most correct. Same heat generated regardless of time but the fact that it has a chance to dissipate during the fill reduces the need to top off or overfill IMHO. The lower the gas or cylinder temp at the end of the fill the less pressure loss due to cooling after the fill whip is removed.
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Re: Shops in the area that fill using a water bath

Post by CaptnJack » Thu Oct 17, 2013 3:21 pm

rcontrera wrote:
CaptnJack wrote:This is much different than a steel tube set in the floor. The mesh baskets distribute the force of a rupture in many directions.


Oh ... OK . Now I understand the mortar reference. (It's tough getting old :rawlings: )

Yeah, a pop can set into the floor would be almost as dangerous as not having one at all. Especially since the fill station operator would most likely be occasionally standing directly in the blast zone. In the fire department fill box above, you have to close the door to fill and the pop can has a blast floor and ceiling inside to prevent shrapnel escape but lots of escape paths for the air.


As long as you don't stand over them, they'll just blow off the roof. What could go wrong eh? :D
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Re: Shops in the area that fill using a water bath

Post by Jeff Pack » Thu Oct 17, 2013 2:10 pm

For water bath, you really need to use a water cooling system for it, like my tig welder uses to water cool the torch, otherwise the water just warms up, and says warm.
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Re: Shops in the area that fill using a water bath

Post by rcontrera » Thu Oct 17, 2013 2:06 pm

CaptnJack wrote:This is much different than a steel tube set in the floor. The mesh baskets distribute the force of a rupture in many directions.


Oh ... OK . Now I understand the mortar reference. (It's tough getting old :rawlings: )

Yeah, a pop can set into the floor would be almost as dangerous as not having one at all. Especially since the fill station operator would most likely be occasionally standing directly in the blast zone. In the fire department fill box above, you have to close the door to fill and the pop can has a blast floor and ceiling inside to prevent shrapnel escape but lots of escape paths for the air.

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Re: Shops in the area that fill using a water bath

Post by CaptnJack » Thu Oct 17, 2013 1:00 pm

If I fill bank bottles or 4 AL80s at a time they don't cool down more than ~200 psi. HP fills from empty cool down about 400 psi no matter what I do, that gas is just much hotter and steel is a poor conductor of heat compared to aluminum.
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Re: Shops in the area that fill using a water bath

Post by Desert Diver » Thu Oct 17, 2013 12:03 pm

I fill 2 HP100's or 120's at a time with my toy 1.9cfm compressor. Takes over an hour, I run them to 3700 or so and still need to come back and top them off when they cool. I have a double barreled mortar sitting here but have never filled it with water and used it. I'll be trying that and report.

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Re: Shops in the area that fill using a water bath

Post by CaptnJack » Thu Oct 17, 2013 11:58 am

Mateo1147 wrote:My LDS doesn't use a water bath and has two articles post on the wall that support the practice of dry filling. He has also taught me the thumb over opening pressure purge to try and be sure not to blow water / debris into tanks when filling.


Be extremely careful putting any body part close to a high pressure gas outlet (fill whip or a tank). You can actually blow gas hard enough on your skin to force air into/under your skin and essentially give yourself an embolism this way. Although its obviously less life threatening than a venous or arterial embolism. Ditto foreign objects like a little sliver of brass from the threads on a DIN valve, or sand etc.

Mateo1147 wrote:The slower the fill rate the less heat generated. Wasn't it the master on Kung Fu that always told Grasshopper to have patience?


Not exactly. There's the same amount of heat of compression going to 500 to 3000 psi in 3 minutes vs. 20 mins (in joules or whatever unit you want to measure in). That heat just has more time to dissipate during the 20 min fill so that at the end of your fill time the gas isn't as hot. Hence the lower pressure drop upon cooling from the slow fill. Same total heat generated just more heat was lost in the extra 17mins of fill time.
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Re: Shops in the area that fill using a water bath

Post by Mateo1147 » Thu Oct 17, 2013 11:37 am

fmerkel wrote:
CaptnJack wrote: generally in a splatter pattern on the bottoms.


That's been my experience. No longer filling at a shop with a water bath, no more tumbles. But, I'm also diligent now to purge the valve.

My LDS doesn't use a water bath and has two articles post on the wall that support the practice of dry filling. He has also taught me the thumb over opening pressure purge to try and be sure not to blow water / debris into tanks when filling. His other mantra is that slower filling is better filling. The slower the fill rate the less heat generated. Wasn't it the master on Kung Fu that always told Grasshopper to have patience?
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Re: Shops in the area that fill using a water bath

Post by fmerkel » Thu Oct 17, 2013 10:29 am

CaptnJack wrote: generally in a splatter pattern on the bottoms.


That's been my experience. No longer filling at a shop with a water bath, no more tumbles. But, I'm also diligent now to purge the valve.
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Re: Shops in the area that fill using a water bath

Post by CaptnJack » Thu Oct 17, 2013 8:24 am

rcontrera wrote:
CaptnJack wrote:sounds alot like a mortar to me ;)

That is the idea. If a tank fails, the "pop can" directs the force of the blast straight up instead of out. Most dive shops don't use them because they are expensive. Plus, as has already been mentioned, you can't drop a set of twins into them.

Image


This is much different than a steel tube set in the floor. The mesh baskets distribute the force of a rupture in many directions.

nwbobber wrote:This is an interesting subject. I keep hearing about the water bath causing water problems inside the tank. This could only happen if there were water somewhere on the whip or the valve before the whip was pressurized, otherwise the pressure differential would keep the water at bay. Can the higher temperature differential be causing condensation on the walls of the tank during the fill, thus causing flash rust? If so it would seem filling slower would be the best way, keep the delta T to a minimum.


No properly filtered air has a way lower dew point than this (-65F).
The issue with water baths is that people either drop the whip into the bucket or it gets into the valve opening when the tanks are dunked, this is especially likely if the tanks are put into the bath before the whips are hooked up. Basically having lots of water around the whip/valve at fill time generally means some gets into the whip or valve opening and then blow into the tanks during the fill. A few drops each eventually evaporating (in the dry fill gas) still leads to corrosion where it sprays into the tanks, generally in a splatter pattern on the bottoms.
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Re: Shops in the area that fill using a water bath

Post by BillZ » Thu Oct 17, 2013 7:56 am

nwbobber wrote:This is an interesting subject. I keep hearing about the water bath causing water problems inside the tank. This could only happen if there were water somewhere on the whip or the valve before the whip was pressurized, otherwise the pressure differential would keep the water at bay. Can the higher temperature differential be causing condensation on the walls of the tank during the fill, thus causing flash rust? If so it would seem filling slower would be the best way, keep the delta T to a minimum.



Not if you have dry air inside your tank, which you should have unless the compressor filtration where you got your fill is bad. It takes moisture in the air to cause condensation.

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Re: Shops in the area that fill using a water bath

Post by nwbobber » Thu Oct 17, 2013 6:27 am

This is an interesting subject. I keep hearing about the water bath causing water problems inside the tank. This could only happen if there were water somewhere on the whip or the valve before the whip was pressurized, otherwise the pressure differential would keep the water at bay. Can the higher temperature differential be causing condensation on the walls of the tank during the fill, thus causing flash rust? If so it would seem filling slower would be the best way, keep the delta T to a minimum.
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Re: Shops in the area that fill using a water bath

Post by rcontrera » Wed Oct 16, 2013 5:54 pm

CaptnJack wrote:sounds alot like a mortar to me ;)

That is the idea. If a tank fails, the "pop can" directs the force of the blast straight up instead of out. Most dive shops don't use them because they are expensive. Plus, as has already been mentioned, you can't drop a set of twins into them.

Image

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Re: Shops in the area that fill using a water bath

Post by Nwbrewer » Wed Oct 16, 2013 8:32 am

CaptnJack wrote:

However, this
Others basically have heavy wall pipe you drop the tank into it
sounds alot like a mortar to me ;)


But that makes it your neighbor's problem, not yours! :taco:
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Re: Shops in the area that fill using a water bath

Post by CaptnJack » Tue Oct 15, 2013 10:36 pm

Nwcid wrote:One thing I have found interesting is that in Fire/EMS filling tanks is generally done in some kind of "container". A lot of fire stations have big steel enclosures that the tanks go in. Others basically have heavy wall pipe you drop the tank into it.

I have not seen anything like that in SCUBA yet.



They exist and are commercially available. Scott Christopher's fill station has one although it won't hold doubles.

However, this
Others basically have heavy wall pipe you drop the tank into it
sounds alot like a mortar to me ;)
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Re: Shops in the area that fill using a water bath

Post by Nwcid » Tue Oct 15, 2013 10:21 pm

One thing I have found interesting is that in Fire/EMS filling tanks is generally done in some kind of "container". A lot of fire stations have big steel enclosures that the tanks go in. Others basically have heavy wall pipe you drop the tank into it.

I have not seen anything like that in SCUBA yet.
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Re: Shops in the area that fill using a water bath

Post by coulterboy » Tue Oct 15, 2013 9:58 pm

Paulicarp wrote:
CaptnJack wrote:
DiverChris wrote:I believe one of the reasons water baths were used originally was in case a tank failed during filling. The water bath would absorb some of the energy of the explosion.


-Chris


While it sounds plausible, this definitely does not work. The water bath container ends up adding to the shrapnel flying around.


Plus, if the idea is that you fill a tank faster because it's in a water bath, how much faster do imagine you can fill it without increasing the likelihood of causing a catastrophic failure? I really don't want to be the one to find out.


Not naming the LDS, I have witnessed the catastrophic failure you're talking about. No bueno!
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Re: Shops in the area that fill using a water bath

Post by Paulicarp » Tue Oct 15, 2013 9:35 pm

CaptnJack wrote:
DiverChris wrote:I believe one of the reasons water baths were used originally was in case a tank failed during filling. The water bath would absorb some of the energy of the explosion.


-Chris


While it sounds plausible, this definitely does not work. The water bath container ends up adding to the shrapnel flying around.


Plus, if the idea is that you fill a tank faster because it's in a water bath, how much faster do imagine you can fill it without increasing the likelihood of causing a catastrophic failure? I really don't want to be the one to find out.

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Re: Shops in the area that fill using a water bath

Post by CaptnJack » Tue Oct 15, 2013 3:20 pm

DiverChris wrote:I believe one of the reasons water baths were used originally was in case a tank failed during filling. The water bath would absorb some of the energy of the explosion.


-Chris


While it sounds plausible, this definitely does not work. The water bath container ends up adding to the shrapnel flying around.
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Re: Shops in the area that fill using a water bath

Post by DiverChris » Tue Oct 15, 2013 2:40 pm

I believe one of the reasons water baths were used originally was in case a tank failed during filling. The water bath would absorb some of the energy of the explosion.


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Re: Shops in the area that fill using a water bath

Post by Nwbrewer » Tue Oct 15, 2013 2:25 pm

To me as the owner of the tanks being filled, any perceived advantage of the water bath in cooling the tanks is greatly outweighed by the increased chance of negative consequences associated with getting water blown into my tanks.
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Re: Shops in the area that fill using a water bath

Post by kdupreez » Tue Oct 15, 2013 2:17 pm

I know that my steel tanks will drop about 300-350psi when i fill them from my banks.. so all I do is overfill them with about 400psi.. so when they cool down, they are at the pressure i want..

Some shops however will not overfill for liability, so a water bath can help them get to a stable rated pressure easier without giving customers a "short fill" when the tanks have cooled down..
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Re: Shops in the area that fill using a water bath

Post by CaptnJack » Tue Oct 15, 2013 1:50 pm

Desert Diver wrote:
CaptnJack wrote:
FlyinV wrote:The Area = The Northwest
Just wondering since I read an article about filling in a water bath and that it wasn't a useful technique.


The answer is "it depends" on:
fill rate
tank material (steel, aluminum, or composite)
tank size (aka volume to surface area ratio)
starting pressure
ending pressure
air temp
water temp
compressor temp (just started or run for a long time already and making the hottest gas it can on that day?
compressor cooling (extra coils, chilled coils etc)
compressor filtration (ie oversized filters would let the gas from a small compressor cool alot before it even got to the tank)

and probably a few more variables I can't think of off the top of my head.

In some circumstances its useful, in others its not. Given the state of the internets, you will be able to find a virtually infinite number of circumstances and people arguing about it.


So under which of the circumstances would it not provide a benefit assuming water temperature cooler than filling tank temperature?


Topping off partially filled lp108 steel tanks 8 at a time from a 3cfm compressor on a 40F day. The temp difference between the metal of those tanks and ambient air is basically nil. Yes they the gas inside gets warmer, but +1F ends up being inconsequential. Smaller the volume they need, the less heat they will gain and the less useful getting rid of that heat a tiny amount faster will matter.

Remember its the gas inside the tank which is warm. You have to transfer that heat to the metal, then you can either transfer that heat to ambient air or to the water in the bath. The rate limiting step is often the transfer of heat from the gas inside to the tank, not from the tank to its surroundings. This is especially true for steel tanks.

Converssely, filling a 6cf aluminum inflation bottle from a 12cfm compressor a bath makes a huge difference - although you still have to let the 6cf bottle sit in the water for awhile and then retop it to achieve 3000psi. So what's the point if you must retop the bottle 400psi vs 800 psi? You still have to top off your 6cf bottle.

The drop in pressure or lack thereof is what creates people's perception of "useful" or "beneficial". That pressure drop is some sort of nonadradic equation of the variables above. Sometimes the rate of heat transfer is so tiny it becomes not worth the bother or impossible to measure any post fill pressure drop that baths become pointless.
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