Help with tank sizing (math)

[Bob DBF]

It's a monster tank Bob; noticebly bigger that a normal aluminum 80.

just saw your post, sounds like an Al 100.

I see there are Chinese ones on ebay at about $300 new, but then you have to buy a valve and hose and I haven't figured out whether the fill valves are compatible with the metric thread of the Chinese ones.

Make sure, if you buy from eBay, that the tank is DOT certified so you can get a fill. A lot of the Chinese tanks are made for Europe, CE certified, with metric threads, not DOT for authorized use here


Bob

 

[JackD342]

Well, the guy selling it has a little shop in his basement with some used gear and a huge compressor. He told me it was 91cu feet and it is much larger than the 80 and 65 sitting next to it. I didn't think to take a photo. It did have a hydro stamp 8-18 and he said if I paid for a VIS sticker he would put one on. I know, sketchy. I'm looking into alternatives. Plus it is kinda pricey. He did have an aluminum tap valve for $30 and a good brass one for a hundred over the tank price.
It is a Scuba tank, Catalina I think. 1999. Definitely limited to 3000psi. I asked if it could go 10% over. He said no. and yes 100 bar is about 1500 give or take since I'm at 800 altitude.

Sounds like some communication distortion, probably on his end. I am thinking it may be a Catalina 3300psi, 100cf. If he is saying that HE won't fill more than 3000, that fill would then be close to 91. A 3300 aluminum cylinder is not a +10% rating, it is straight up 3300 with standard hydro test, no REE required. Both numbers should be stamped on it. How much is he asking? And do you already have the connection for your airgun fill? That may affect what valve you get. (yoke, DIN, convertible) But your valve descriptions are worrying me too. What do you mean by "aluminum tap valve?" All scuba valves are brass, not counting a few parts. And $100, even new, is not a common scuba valve. If a scuba cylinder has been modified for some other type of gas valve, I'm out.

 

[Bob DBF]

But your valve descriptions are worrying me too. What do you mean by "aluminum tap valve?" All scuba valves are brass, not counting a few parts. And $100, even new, is not a common scuba valve. If a scuba cylinder has been modified for some other type of gas valve, I'm out.

It may be a paintball fill valve made to fit a SCUBA tank.


Bob

 

[JackD342]

Well, the guy selling it has a little shop in his basement with some used gear and a huge compressor. He told me it was 91cu feet and it is much larger than the 80 and 65 sitting next to it. I didn't think to take a photo. It did have a hydro stamp 8-18 and he said if I paid for a VIS sticker he would put one on. I know, sketchy. I'm looking into alternatives. Plus it is kinda pricey. He did have an aluminum tap valve for $30 and a good brass one for a hundred over the tank price.
It is a Scuba tank, Catalina I think. 1999. Definitely limited to 3000psi. I asked if it could go 10% over. He said no. and yes 100 bar is about 1500 give or take since I'm at 800 altitude.

You need a new conversion tool! The calculator on my Windows phone (yeah, that's not a typo) says 100cc is 6.1 cu in, or 0.42 coffee cups.
So, let's say you have a 100cf 3300psi cylinder only filled to 3000.
And you want to fill your gun that already has 100bar/1450psi topped back up to 2700psi. I calculate you will get just under 31 top ups before they will start to be less than 2700psi.
In practice it will be a little less, as you will bleed some pressure off every time you connect/disconnect your filling hoses/adapters. Better yet, if that cylinder starts at 3300, then double the fills.

 

[dberry]

I was ready to post that 100cc = 6.1 cubic inches, not 68, but JackD342 beat me to it.

 

[Fats]

Sounds like some communication distortion, probably on his end. I am thinking it may be a Catalina 3300psi, 100cf. If he is saying that HE won't fill more than 3000, that fill would then be close to 91. A 3300 aluminum cylinder is not a +10% rating, it is straight up 3300 with standard hydro test, no REE required. Both numbers should be stamped on it. How much is he asking? And do you already have the connection for your airgun fill? That may affect what valve you get. (yoke, DIN, convertible) But your valve descriptions are worrying me too. What do you mean by "aluminum tap valve?" All scuba valves are brass, not counting a few parts. And $100, even new, is not a common scuba valve. If a scuba cylinder has been modified for some other type of gas valve, I'm out.

You may be right. The cylinder has not been modified. I remember it being noticeably fatter than the 80 and about the same length maybe an inch or two taller? He is asking 150 + 30 for the rectangular aluminum clamp-on (yoke) tap or + 100 for the standard sort of chromed brass scuba hoop-style clamp-on (I say clamp-on meaning screws up like a clamp. I think it is the yoke type as you say). I do not yet have a hose, valve, bleed screw, and adapter to fit the yoke.

After what you said about the 3300 filled to 3000 I am thinking that there may be some corrosion inside that tank and maybe he is afraid to fill it to spec. Not a good sign. Have you seen any of those carbon cylinders from China?
(Air Rifle use 86 cu ft 4500psi Scuba Tank 2018 Gas Cylinder 300bar Carbon Fiber | eBay)
I'm guessing if i got one of those I might have trouble getting it filled, so I'm leaning towards the $200 hpa pump that is made in China. I saw a youtube video of a German air gunner who bought one, took it apart, and thought it not a bad deal at all.

 

[Fats]

just saw your post, sounds like an Al 100.



Make sure, if you buy from eBay, that the tank is DOT certified so you can get a fill. A lot of the Chinese tanks are made for Europe, CE certified, with metric threads, not DOT for authorized use here


Bob

Thanks Bob!
I was worried when I saw the Chinese tanks had metric threads. So DOT means only US threads? Or could there be a DOT certified metric tank?
(Air Rifle use 86 cu ft 4500psi Scuba Tank 2018 Gas Cylinder 300bar Carbon Fiber | eBay)

 

[Fats]

It may be a paintball fill valve made to fit a SCUBA tank.


Bob

I don't know about Paintball stuff, but it is just an aluminum rectangle about 1/2 inch thick with a cutout to make it a scuba yoke.

 

[Fats]

You need a new conversion tool! The calculator on my Windows phone (yeah, that's not a typo) says 100cc is 6.1 cu in, or 0.42 coffee cups.
So, let's say you have a 100cf 3300psi cylinder only filled to 3000.
And you want to fill your gun that already has 100bar/1450psi topped back up to 2700psi. I calculate you will get just under 31 top ups before they will start to be less than 2700psi.
In practice it will be a little less, as you will bleed some pressure off every time you connect/disconnect your filling hoses/adapters. Better yet, if that cylinder starts at 3300, then double the fills.

Well, I need a new brain. This one's not getting any younger. But I think it's too expensive, too heavy, and too "iffy" so I'm probably just going to buy a pump.

 

[rhwestfall]

those are air gun adapters for filling PCP guns off yoke scuba tank valves...

I used them as a cheap transfill by purchasing 2, a PCP hose, and a double male QD,,,,

YMMV