Cooling tanks before filling

[Sintax604]

Logistics dictate that my tanks have to sit in my car all day while I'm at work before I can stop in the shop to get them filled. Now that it's summer the tanks end up roasting in the car and can be quite hot to touch by the time I make it to the shop.

So far I've been leaving the tanks with the shop overnight and having them filled and picked up the next day to avoid short fills and extra stress on the tanks. It just ocurred to me that if I was to open the valve and quickly bleed off most of the remaining air (I usually have 500-1000psi left), the tank would cool down.

I haven't tried this yet so I don't know how effective the cooling will be but does anyone have reservations about this idea or a better idea for getting the job done?

Many thanks!

 

[300bar]

Tanks would indeed cool down somewhat but if it would be of much use.
It might be the same as putting a tank in water.No use what so ever.Heat production happens on the inside of a tank.(we did try this with our compressor maintenance company)
The way you do it now IMO is the best way.Fill-let cool down and topoff.
The other option we found and is running at a diveshop overhere,is deepfreezing compreesed air in the casade.Works fine but costs are skyhigh.

 

[Indian Valley Scuba]

Hey there Sintax -

Rapid cooling by the pressure drop method (letting the air blast our of the tank valve) can cause any moisture contained in the gas remaining in the tank to actually condense on the interior of the tank or valve. I know, the air you get is supposed to be very low in moisture content, but unless your filler is religious in replacing their dryer cartridge, or uses a refrigerated cooling system, then it has moisture (humidity) trapped in it.

So now, when you refill it, the condensate that formed needs to re-vaporize into the new gas. While it remains on the walls or bottom of your tank, it can do whatever it can to corrode the tank, similar to any other water you may get in your tank.

Regarding your concern about stress, there is no measurable degree of increasded stress in filling a warm cylinder versus a cold one. In fact, since the cylinder will actually warm while filling, due to the compression of the gas being put itto it, then starting with a warm cylinder will in fact reduce stress, since there is less of a temperature change. however, as I noted, the stress factor in talking about differences from 40 degrees F to 140 degrees F is insignificant.

If you are concerned about a short fill, suggest that your shop fill the tank, then let it sit at the fill station, with the fill whip connected, and the fill station regulator set at the desired end pressure. As the gas in the tank cools, and the volume is reduced, then more gas will be allowed to pass through the regulator and enter the tank.

If your fill station doesn't have a regulator on their output, then you are stuck with the "turn many valves, day after day" method of shufling from cascade bottle to cascade, and reading tank pressure off a gauge. Find a shop that uses a regulated supply system and get complete fills, every time. Short of that, have them fill them the night you drop them off, then top them off the few hundred psi they need when you pick them up. The fill will be much more accurate.

Hope this helps you in your decision making!

 

[Walter]

Lay several towels over the tanks. They won't be as hot when you get to the shop.

 

[cool_hardware52]

Logistics dictate that my tanks have to sit in my car all day while I'm at work before I can stop in the shop to get them filled. Now that it's summer the tanks end up roasting in the car and can be quite hot to touch by the time I make it to the shop.

So far I've been leaving the tanks with the shop overnight and having them filled and picked up the next day to avoid short fills and extra stress on the tanks. It just ocurred to me that if I was to open the valve and quickly bleed off most of the remaining air (I usually have 500-1000psi left), the tank would cool down.

I haven't tried this yet so I don't know how effective the cooling will be but does anyone have reservations about this idea or a better idea for getting the job done?

Many thanks!

When gas expands it cools and when it is compressed it heats up.

Whatever cooling you gain by venting will be lost by the heat of compressing that same amount of gas back into your tank. No net gain, sorry. In fact depending on the fill station the gas being introduced into your cylinder maybe at a higher initial temperature than the "hot" remaining gas in your tank.

BTW, if venting your gas results in condensing moisture on the inside of your tank you need to find a new fill station.

Wet gas is an indication that the entire filter apparatus has failed and is passing moisture AND other nasty stuff.

Tobin

 

[divinginn]

I keep the ac cranked up high on my truck on the way there to cool them off some,not sure how much good it does but cannot see where it would hurt. My tanks get very hot sitting in the truck all day during work before I get off and take them to get filled.

 

[chrisc]

Becareful leaving tanks in hot cars... I had 1 burst disk let go while driving scared the ***** out of me and the cars around me. Don't know why it happened, had 7 other tanks in the rack with no problem and it was mid morning and only 90 outside.

 

[Sintax604]

Thanks a bunch for all the great info and ideas! I didn't think about the mosture issue at all. And I'll definitly give the towel trick a try.

 

[SparticleBrane]

It might be the same as putting a tank in water.No use what so ever.Heat production happens on the inside of a tank.(we did try this with our compressor maintenance company)

And yet this happens every day in cave country in Florida, and their fills are great.

Using a water bath works very nicely. Just because the inside of the cylinder heats up doesn't mean that the heat can't be transferred to the water surrounding it -- in fact, it transfers quite quickly and efficiently.


If you have moisture condensing inside your cylinder, then the air being put in there by the shop is dirty. Grade-E air is supposed to have a dew point of -65F or something ridiculously low.

 

[Gombessa]

And yet this happens every day in cave country in Florida, and their fills are great.

Using a water bath works very nicely. Just because the inside of the cylinder heats up doesn't mean that the heat can't be transferred to the water surrounding it -- in fact, it transfers quite quickly and efficiently.

Agreed. If you take two tanks, one dry and one in water, and fill the crap out of both of them and immediately pull the immersed tank out, maybe you wouldn't see much of a difference.

But, IME if you slow fill, and give each a few minutes of cool-down time before topping off, the immersed tank is significantly cooler, and nets a couple hundred PSI more than the dry tank.