Anyone know about twin 50's?

[kramynot2000]

I've seen a few sets of twin 50's on ebay and was wondering about these. It looks like a very compact design. Does anyone know what the neck threads are on these? I was thinking of maybe picking up a set cheap and swapping the manifold for a more modern two valve manifold.

Also, how much do these 50's weigh?

Thanks,
Tony

 

[Don Burke]

kramynot2000 once bubbled... I've seen a few sets of twin 50's on ebay and was wondering about these. It looks like a very compact design. Does anyone know what the neck threads are on these? I was thinking of maybe picking up a set cheap and swapping the manifold for a more modern two valve manifold.

Also, how much do these 50's weigh?

Thanks,
Tony

Watch youself. Many of them have the old half inch thread and some are the tapered thread.


This one is overpriced and the 1800psig rating tells me they are actually fire extinguisher bottles. Also note the reducers in the necks of the bottles. These tanks should be very light.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3630952402&category=16057

caveat emptor

 

[DA Aquamaster]

The reducers are a little odd and it makes you wonder what's what, but the 1800 psi service rating does not mean fire extinguisher bottle.

I have seen, used and owned both a set of 2015 psi steel 50's and a set of 1800 psi steel 50's and both sets were genuine came-that-way-from-the-factory scuba tanks. The 1800 psi tanks were a few inches taller than the 2015's but both styles were 6.75 in dia and weighed about the same. I'm working from memory here but I think the total weight with manifold and bands was around 50 lbs.

One issue with the 2015 psi variety of steel 50 is that they are too short to work with the nominal 11" spacing on most backplates. The back pack that came with them used a shorter spacing. In that regard the taller 1800 psi tanks are more functional and usable with a modern backplate and the 2015's will be really hard to use as doubles unless you drill another hole in your backplate.

Also, the capacity is closer to 45 cu ft with 50 cu ft. being what you got with a 10% overfill.

I broke up both sets for my son to use when he was younger and have since sold all four tanks so I can't give you much more information.

 

[Don Burke]

DA Aquamaster once bubbled... The reducers are a little odd and it makes you wonder what's what, but the 1800 psi service rating does not mean fire extinguisher bottle.

I have seen, used and owned both a set of 2015 psi steel 50's and a set of 1800 psi steel 50's and both sets were genuine came-that-way-from-the-factory scuba tanks. The 1800 psi tanks were a few inches taller than the 2015's but both styles were 6.75 in dia and weighed about the same. I'm working from memory here but I think the total weight with manifold and bands was around 50 lbs.

One issue with the 2015 psi variety of steel 50 is that they are too short to work with the nominal 11" spacing on most backplates. The back pack that came with them used a shorter spacing. In that regard the taller 1800 psi tanks are more functional and usable with a modern backplate and the 2015's will be really hard to use as doubles unless you drill another hole in your backplate.

Also, the capacity is closer to 45 cu ft with 50 cu ft. being what you got with a 10% overfill.

I broke up both sets for my son to use when he was younger and have since sold all four tanks so I can't give you much more information.

I hadn't seen the 1800psig dive bottles. Thanks for the correction.

Nice catch.

 

[Bob3]

I have a set of old 1950s vintage USN twin 50s out in the shop, they have 1" necks on them. No "+" rating, they're straight 50 cu ft @1800 psi.

If they have the 3/4" straight o-ring sealing thread you can do the "modern" valve thing.
The critters have a very sweet trim & balance thing going for them, if you try a set you'll probably fall in love with them, especially if you're used to diving aluminum 80s.

 

[Don Burke]

Bob3 once bubbled... I have a set of old 1950s vintage USN twin 50s out in the shop, they have 1" necks on them. No "+" rating, they're straight 50 cu ft @1800 psi.

If they have the 3/4" straight o-ring sealing thread you can do the "modern" valve thing.
The critters have a very sweet trim & balance thing going for them, if you try a set you'll probably fall in love with them, especially if you're used to diving aluminum 80s.

That might be the solution to the mystery of the reducers on the eBay tanks. I wonder if a set of reducers to take the one inch tanks to 3/4 would be reasonably priced.

After diving double AL80s, the small steel tanks (I have 72s) are like heaven. I'm going to see if I can figure out how to safely dive them in a wetsuit.

 

[Bob3]

That might be the solution to the mystery of the reducers on the eBay tanks.

The threads on the tanks *should* be NGT threads, as well as the manifold. The bushings are *probably* NPT. They may well have stressed the threads, as when using too much teflon tape. (loads the thread tips, not the whole depth of the thread).
The critters may well be junk due to damaged threads.

I used to dive twin 72s quite a bit, tore them all down to singles.
The "problem" with diving doubles in a wetsuit is a recent invention that shouldn't extend to twin 72s.
Your mileage may vary depending on your gear configuration, push a pencil around a bit & see what you come up with.

 

[Bob3]

I found a pic of the set I have, note the gigantic o-ring...

 

[Don Burke]

Bob3 once bubbled... I used to dive twin 72s quite a bit, tore them all down to singles.
The "problem" with diving doubles in a wetsuit is a recent invention that shouldn't extend to twin 72s.
Your mileage may vary depending on your gear configuration, push a pencil around a bit & see what you come up with.

With the 72s, my steel backplate, and my wetsuit, I'm about two pounds negative in freshwater at 400psig.

An ABS backplate is a change of about four pounds and going to saltwater would be about another seven, which (minus the two pounds above) would give me nine pounds of ditchable weight. That should be enough to get me to the surface with full tanks and a failed wing.

I'm looking/asking around to see if someone has an ABS backplate I can borrow for a test in the ocean (I'm not sure enough to buy one.). If it works, the set of AL80s won't get quite so much use except in lakes and quarries.

 

[kramynot2000]

All the recent discussion about small doubles really has me thinking and I guess curious. I love my double HP80s but am looking for something a little lighter that I can hike into the mountains for some lake diving. I think the 50 lbs is still too heavy for that. An AL80 is only 30 lbs so that still seems to be the lightest choice, although I do love diving doubles!

Tony