Getting the max out of scuba tanks

gn303 · Post by **gn303** » Mon Nov 12, 2012 2:40 pm

I'm filling my AP cylinders from a scuba tank, like most of us do I guess. I can usually get 5 to 6 refills with the manometer of the cylinder reaching 200 bar. I was wondering if it would harm the cylinders if I put then in a freezer (5-10 min) and fill them from a tank that is at room temperature?
I guess it's alright, but I rather ask your opinions first (rather that having regrets later :-).
Thanks for your considerations.

Guy

jhmartin · Post by **jhmartin** » Mon Nov 12, 2012 3:09 pm

This works to a great extent with CO2, but not so much with air.

With air you get a tiny weeny tweak more into the cylinder, more I think from keeping the expansion caused temperature low rather than any density difference in the gas due to temp.

dschaller · Post by **dschaller** » Mon Nov 12, 2012 3:11 pm

Cooling off the tank will not make a significant difference for compressed air (unlike CO2).

Isabel1130 · Post by **Isabel1130** » Mon Nov 12, 2012 4:31 pm

I find the whole scuba thank thing horribly frustrating, especially since the closest place to fill it is 60 miles away. If I get one large enough to get several fills out of, I need help to move it. Small enough to move, it has to be refilled too often.
I bought a pump, and have been much happier.

shooter560 · Post by **shooter560** » Mon Nov 12, 2012 4:48 pm

What pressure tank are you using? I have a 7lt 300bar tank and so far I'm still getting 200 bar in my pistol cylinder after 30 refills , all you have to do is fill slowly and watch the cylinder manometer to make sure its topped up properly

j-team · Post by **j-team** » Mon Nov 12, 2012 5:39 pm

So what if you don't get 200bar fills every time?

The pistol has a regulator and only needs about 30bar to work, so even if your SCUBA tank is down to 150bar you will still easily get enough air to shoot a match and final. I only get mine filled when it gets to about 140bar and I'm only 5 minutes from my local dive shop.

gn303 · Post by **gn303** » Tue Nov 13, 2012 10:50 am

Thank you for your suggestions. The general conclusion is that it isn't worth the hassle.
Indeed the pistol doesn't need 200 bar, but I feel better starting a competition will a cylinder top filled. I'm using a 'regular' scuba tank approved to 200 Bar. The shop owner is willing to put a little more (e.g. 5 bar) but that's it. And I think he's right.
Thank you and continue to enjoy shooting.
Guy

rmca · Post by **rmca** » Tue Nov 13, 2012 11:09 am

I personally have a pump, but some of my shooting mates do fill their cylinders with a tank. What they normally do before a competition is ask me for my pump to top off their cylinders just for peace of mind.

You could do the same... use your tank to fill the cylinders and then top them off with a pump. It´s far less work than the pump alone ;)
Also with a pump you never run out of air...

Good shooting

John C · Post by **John C** » Tue Nov 13, 2012 2:48 pm

You can also get a second scuba tank. Use the one with the lower pressure to initially fill the cylinder, then top off with the second tank. You can drain the lower tank almost to empty, which will dramatically increase the amount of usable air you get out of a scuba tank. Then you refill the empty tank, and it becomes your "full" cylinder, and your previous "full" tank becomes the the first tank.

I just bought a used, full scuba tank with fresh hydro for $100 from a scuba shop, so the price here isn't prohibitive.

The issue with pumping, from what I understand, is that if you're in a humid environment, moisture can enter the cylinder, causing corrosion. Although there are air dryer attachments for pumps, scuba air is bone dry.

-John