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Post by scubadiverbob on Jul 3, 2007 20:54:58 GMT -8
Just a thought that came to my mind ... I wonder if the person, who was rich enough to pay over $1000, has his own compressor? (well, everyones talking about hydros and vis inspections). Of course, I'm not implying someone would fill their own tanks that were out of hydro ...
I was told what causes cracks in the neck was over tightening the valve after doing a vis.
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Post by SeaRat on Jul 3, 2007 22:30:19 GMT -8
Bob,
I don't think it is overtightening the valve, but I'll let Luis talk to the specifics. I have heard that it is the tanks under constant stress from the fill over time that creates the crack, caused by imperfections in the neck of the cylinder. Some people over-fill these tanks too, which would be bad for them. There is a term for this kind of stress, which I cannot think of right now. Luis, what is it?
John
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Post by time2dive on Jul 4, 2007 0:18:55 GMT -8
Sustained Load Cracking
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Post by luis on Jul 4, 2007 3:18:40 GMT -8
Bob, I don't think it is overtightening the valve, but I'll let Luis talk to the specifics. I have heard that it is the tanks under constant stress from the fill over time that creates the crack, caused by imperfections in the neck of the cylinder. Some people over-fill these tanks too, which would be bad for them. There is a term for this kind of stress, which I cannot think of right now. Luis, what is it? John Are you referring about hoop stresses? I mentioned it on mt first post. Hoop stress is the primary stress experienced by a cylindrical pressure vessel. It occurs tangential to the cylinder wall. Sustain Load Cracking is the result of sustained hoop stresses (not valve torque). It occurs from the cylinder being exposed to stress (due to pressure) for extended periods of time. I have examined several tanks with crack, I even had the neck cut off of a couple of tanks for closer inspection, and there was no mechanical damage to the threads (from over torquing, etc.). The cracks looked like classic brittle failure originating at a minute imperfection or "crack starter": perhaps can also be consider a stress riser. The crack plane (for SLC) is perfectly perpendicular to the hoop stresses as expected.
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Post by SeaRat on Jul 4, 2007 7:33:40 GMT -8
Sustained Load Cracking, that was what I was trying to remember yesterday. Luis, thanks for the explainations. I appreciate this amount of detail. My hope is to keep my UDS-1 going, but if worst comes to worst, I would probably trade them for some new cylinders from the LDS, who's owner does collect old gear (which she doesn't dive). At one point, I'd like to set up a set of small doubles, much like the jump tanks we had in the USAF. Those tanks were twin 42s, made from twenty-man life raft bottles that we had tapped to a 1/2 inch tapered thread for scuba tanks. They were very nice, and could be used with double hose regulators too. Here's a photo of them: I had to have those tanks drilled, as the threads were no longer stable. The USAF got rid of theirs too. But in the 1960-1980s, they were used as our jump tanks, and sometimes traded to the US Navy. The Navy divers did not like the extremely heavy doubles they had, and these filled a need when we traded them. But, I would like to keep the UDS-1 going as long as possible. John
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Post by Michel on Jul 4, 2007 12:14:24 GMT -8
I'll trade my UDS-1 with broken filler hose pin for 2 RAM hp nozzles with or without the guts! I,ve given up on the aggravation of owning a UDS-1 system! Other wise it was a fabulous system when new! Michel A.
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jviss
Pro Diver
Posts: 209
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Post by jviss on Aug 11, 2007 4:23:49 GMT -8
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Post by nemrod on Aug 11, 2007 12:26:11 GMT -8
I don't think it should be a aurprise they are selling beyond 1,000 dollars, heck, a 50 dollar Voit with rotten hoses and two tinnermans went for over 600 dollars ! I don't think it is insanity, perhaps desperation? Perhaps somebody just wants it really bad.
It would not take exactly super science to build them new using aluminum30 cf cylinders, tube manifolds and even a recess built in for the double hose. Once could even build a wing type BC, something small like an OxyCheq Razor 18 into the underside.
The real problem with these units is lackof portability, nobody carries their tanks on vacation to Bonaire and a system that incorporates tank is a airline nightmare.
Nemrod
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Post by SeaRat on Aug 11, 2007 17:31:12 GMT -8
'Sounds like I'm about the only one still diving a UDS-1. I had it out about two weeks ago, and thoroughly enjoyed it. Nemrod, the UDS-1 became a problem almost as soon as it was introduced. Dive shops hated it, it was hard to maintain, VIPs cost 3x as much (three cylinders), and three engineering problems had to be solved before they were "nice" in the water. Here's the engineering problems: --The main one is the upside-down valve assembly caused a buoyancy problem at the top end--the top tended to float above the diver's back, and then the large surface area "caught" the water very badly, causing a lot of drag. --The harness system was not made for the USA, and included a waist strap (which shouldn't have been used, as it was meant to hook the crotch strap into the weight belt, the same as the Quad rigs used in "World Without Sun," Cousteau's second Academy Award Winning film. --The filler hose had a problem with the one-way valve, which leaked air and kept that hose pressurized. That made it exceedingly hard to get off the knob that was designed to hold it. Concerning sustained load cracking, I found this website by looking on the one above, and following the link. It is interesting how Luxfer in Australia views sustained load cracking: www.luxfercylinders.com/support/faq/sustainedloadcracking-australia.shtml#q3John
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Post by duckbill on Aug 11, 2007 22:36:00 GMT -8
"Last Hydro/VIP June 2006" They didn't mention if it had the VIP-plus performed or not. Would be nice to know.
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Post by BLT on Aug 12, 2007 0:25:35 GMT -8
WOW!!! That's quite a different spin than you usually hear about SLC and those evil "dangerous" aluminum tanks. I have had the same opinion of the al80's that Luxfer does. Yes, there are some problems with the older tanks alloy, but, to use Luxfers statistic, only about 1.25% of their tanks exhibit the SLC and (again using their numbers) out of the 40 million or so Aluminum tanks of all alloys, there have only been about 20 that have exploded globally. I have always considered them safe, especially when subjected to proper inspections and care, such as slow fills and not overfilling them. Just think about those 40 million tanks. How many are in third world nation resorts, being subjected to instantaneous fills, overfilling, getting breathed down to empty allowing saltwater in then getting left in the sea air before getting tossed into a panga with a bunch more tanks? If they were really the ticking time bomb that people on the internet claim they are, you would be hearing about them exploding on a weekly basis, and that simply isn't happening. Yes, there have been a couple tragic incidents over the past twenty years or so, but we can never forget that the cylinders are considered to be hazardous materials and needed to be treated as such and will always have a certain amount of inherent risk attached to them... (excuse me as I step down off my soapbox)
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Post by Broxton Carol on Aug 12, 2007 5:29:53 GMT -8
Regarding the comments about 50 dollar voits, those voit regs havent been 50 dollars since they were new. They have fluctuated with the market up and down and now are riding the crest. Over the past few months they have sold, the early green label single stage, and da types and the popular navy model too, from 500 to over 1800 dollars. These early ones are spurred on by the charisma of the SEA HUNT series of the 1950's, and this gear is at a premium because of its association to Mike Nelson the star character. Yesterday a vulcan knife, worth perhaps 25.00 sold for over 300.00 to some collector. There will be vulcan knives, and green voits appearing in the future, and there will be an appreciating number of divers and collectors who will recognise their intrinsic value, and buy them for investment, as well as diving enjoyment.
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Post by nemrod on Aug 12, 2007 20:04:06 GMT -8
I would be cautious about considering some of these things investments in the strictest since. It is a great hobby to collect, restore etc but there are only about five people putting the pressure on the Voit market for example. No guarantees in the stock market either of course but if those five people quit bidding every Voit or rare USD then what? Just how deep is this market really? Now, if all those new Voits and USD Aqua Master that we all saw, myself included, being thrown in dumpsters and tossed into metal scrap we had instead squirrled them away and sold them today to those five people who buy everything on ebay, heck, that would be an investment.
James
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Post by Broxton Carol on Aug 13, 2007 5:04:57 GMT -8
Regarding 5 people bidding in the voit market, look at whats on there now. There are different people bidding on the items, some we know, some newcomers. Though tiffany made thousands of lamps, bronzes, and decorated cabinet vases, they always get strong attention and bids from a large group of investors as well as those who appreciate the inherant value of the aura of a tiffany piece. This market has ripened over the past 30 years and the 500.00 lamp of 1972 is now worth 5000.00! Sure voit regs arent on the same strata, they do have a strong following, as do the rest of the rare marques. Even aquamasters and mistrals are bringing high prices for decent pieces. I sold 2 mistrals in the last 3 weeks to people I never heard of. There are plenty of buyers out there, interested in enjoying the gear we are already accustomed to. Sure there are some greedy ones who have to have it all, and that goes with the territory of collecting, but I see a new "wave" of collectors and divers of vintage gear who will pay the price to make their dream come true.
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Post by Captain on Aug 13, 2007 6:07:25 GMT -8
Regarding 5 people bidding in the voit market, look at whats on there now. There are different people bidding on the items, some we know, some newcomers. Though tiffany made thousands of lamps, bronzes, and decorated cabinet vases, they always get strong attention and bids from a large group of investors as well as those who appreciate the inherant value of the aura of a tiffany piece. This market has ripened over the past 30 years and the 500.00 lamp of 1972 is now worth 5000.00! Sure voit regs arent on the same strata, they do have a strong following, as do the rest of the rare marques. Even aquamasters and mistrals are bringing high prices for decent pieces. I sold 2 mistrals in the last 3 weeks to people I never heard of. There are plenty of buyers out there, interested in enjoying the gear we are already accustomed to. Sure there are some greedy ones who have to have it all, and that goes with the territory of collecting, but I see a new "wave" of collectors and divers of vintage gear who will pay the price to make their dream come true. Exactly as the baby boomers have done to 50's and 60's muscle car prices
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