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Post by ltstanfo on Jan 14, 2009 9:14:17 GMT -8
An interesting question that I hope someone here can shed light on:
Where did the steel 72 come from (both in terms or country of origin and the volume of air)?
Back in the day my instructor told me that it was to give the most air without the chance of entering deco but there has to be more than that... if it is that simple.
So.. anyone? John?
Regards, Ltstanfo
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Post by SeaRat on Jan 14, 2009 10:54:10 GMT -8
I'm pretty sure that the steel 72 originated with U.S. Divers Company in the early 1950s. People before that were using converted fire extinguisher bottles. It may even have been earlier, when Rene had his sporting goods company before it became U.S. Divers Company. But I know that Scott Aviation had different tanks, as did the others. I'll have to look in some of my books at home, but this is my start on the question.
By the way, yes it was difficult to get into decompression problems using a single steel 72 cubic foot tank. At one cubic foot a minute, that gives you 72 minutes using the 10% overfill of a new cylinder. Basically, it was a 71.2 cubic foot of air tank (rather than a "72") at 2475 psi (2250 rated pressure plus the 10% over fill is 225 psi added, or 2475 psi). At a regular fill, it wasn't 71.2 cubic feet of air, but rather 64.7 cubic feet of air. Again, using a 1 cubic foot per minute air consumption rate, that's about 65 minutes at the surface. At 33 feet (twice the pressure) you would have half the air supply, or about 32 minutes of air. At 66 feet (3 times the pressure) you would have one third the air supply that you had an the surface, or about 21 to 22 minutes of air. As you may recall, the rule of thumb for the US Navy dive tables was 60 minutes at 60 feet, so going beyond the no-decompression limits on a single dive and a single 72 was not easy to do.
One other thing about the single 72, it is a very nicely balanced system from a buoyancy standpoint. I don't have the specs in front of me, but diving the single 72 was always easy, as even empty they were just negative buoyancy empty in fresh water, and did not vary too greatly over the dive because of the lower pressure rating.
John
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Post by ltstanfo on Jan 14, 2009 11:21:35 GMT -8
John,
You were pretty much on track with your initial thought:
(From Nick Icorn)
"In 1949, Rene' Bussoz, a distant cousin of the Cousteau family, and owner of "Rene Sports, 1045 Broxton Ave. , in Westwood, California became the first distributor of the diving apparatus, now called the "Aqua-lung".
Using a steel 70 cu. ft. cylinder, which actually held 64.7 cu. ft., a harness and regulator, the unit sold for $160. The regulator by itself was $80.
Many early divers and the people at Scripps used the French regulator combined with surplus twin 38 cu. ft. cylinders.
In 1952, Rene' changed the company name to U.S. Divers Co. In 1955, the operation was moved to Pico Blvd. in Los Angeles."
Gotta love dive history. :-)
Regards, Ltstanfo
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Post by nemrod on Jan 14, 2009 16:30:35 GMT -8
I distinctly remember being told it was "almost" impossible to get bent with a steel 72. Well, that is more or less true though there are quite a few people who could easily extend a dive with one long enough to get nicely bent.
nem
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Post by duckbill on Jan 14, 2009 20:35:19 GMT -8
According to "Basic Scuba", there was a "70-Plus" which held 71.2cf, and a "Standard 70" which held 61.3cf.
The 70-Plus was a 2250 psi tank (2475 psi 10% overfill) which may have later become known as our venerable "72". Or is it?
The Standard 70 was a 2150 psi tank (2365 psi 10% overfill).
I have a 2150 psi cylinder that I believe must be this "Standard 70", and several undisputed 2250 psi steel 72s and both types share nearly, if not exactly, the same dimensions.
But, here's where it gets confusing: --------------------------------------------
Fred's chart shows the Standard 70 to be 61.3cf at the rated 2150 psi, and so 67.4cf at the 10% overfill. Hence the "70" designation (rounded up) AT OVERFILL.
However, then contrary to everything else I have heard, the 70-Plus is shown to be 71.2 AT THE RATED 2250 psi, and so 78.3cf at the 10% overfill.
So, is the 70-Plus a 72? If so, is it 71.2cf at 2250 psi, or at 2475 psi overfill? I've always heard it was only a "72" at the overfill pressure. Did Fred make a mistake here?
Or, is Fred's chart correct, and the 70-Plus was a completely different vessel than our 72s, since the 70-Plus was really an "80" (78.3 rounded up)? Was the 70-Plus the "steel 80" I have heard about? Was the steel 80 a 2150 psi cylinder? Can anyone confirm this?
My 2150 psi cylinder is not in hydro. I don't want to hyro it as it have never been hydroed since it left the factory. Otherwise, simple pressurizing and measuring would tell me if it is a "steel 80" or a "Standard 70".
Can anyone shed some light on this?
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Post by SeaRat on Jan 14, 2009 22:47:59 GMT -8
Duckbill, I don't think we'll get resolution of this one. I just looked through about 14 books, five catelogs, and my NAUI Instructor's manual, and there is a lot of disagreement. Some references even state that the cylinders of a "72" are rated between 1800 psi and 2400 psi. They don't even say "psig." One New England Diver's catalog went so far as to say that they sold both single 71.2 and twins, and that the twins 71.2 system had a capacity of 142.2 cubic feet. They cannot even add sometimes. My take on this is that if Fred Roberts was confused, we all will be! By the way, I had a Voit 80 cubic foot cylinder, and it had a 2250 psig rating, as I recall. It was a bit longer is all (4-6 inches). Here is a photo of me wearing it in 1974: John
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Jan 15, 2009 9:10:10 GMT -8
let me throw some more confusion into this.......
When I first was going thru certification with the YMCA in Fort Worth in 1967 I had to borrow my instructors tank as the borrowed "72" I had was empty.
His tank was yellow USD steel 94 cf he said. It was long and heavy but the same diameter of the 71/2 Healthways I was using with a Healthways doublehose.
I remember stepping off into the pool and my 115 lb body was immedately on the bottom.
Does anyone remember a 94 steel? I have not seen on since.
Mossback
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Post by broxton on Jan 16, 2009 11:00:27 GMT -8
US Divers made both a steel 80 & steel 90 back in the 50's. The 80 was at 2600 psi, and the 90 at 3015 psi. I've never personally seen a steel 90, but I have a few steel 80's and they'll sink you like a rock. You could easily drop 8-10 lbs off your belt with an 80 compared to the 72. The 90 weighed 12 lbs more than the 72.
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Post by william on Oct 1, 2010 13:20:18 GMT -8
One thing I wanted to mention to help, is if you are restoreing your Scuba Tanks for Vintage Diving or for a Living Room Vintage Diving Equipment Display, you will want to do it properly. I think there are several different bottom coats that can be used. One that is Excellent & Easier to use is Meller "Marine Grade" Yellow Zinc Chromate Primer, sold in Boat Supply Stores like West Marine and is designed to bond great for metal parts on Boats, Above & Below Water on Marine Engines, Underwater Outdrives like Rudders, Drive Shafts, Outboard Engines Below the Water Line. So it is perfect for Scuba Tanks that get Hot when they are filled and often are soaked in Saltwater for hours,even days. Works perfectly.It bonds Excellently to Galvanized Metal, Bare Steel & any other types of Metalic Parts & the paint has a Very High amount of Yellow Pigment making coverage super Easy.
{ Never Use made in China Paint. MANY OF THEIR BRANDS OF SPRAYPAINT ARE NO GOOD. FIRST = READ THE LABEL! Like {"Valspar Spraypaint made in China contains LEAD"} and warns about useing it and even sanding it can cause contamination. I thought Lead in paint was Illegal since the 1960s, but it IS in the paint and being sold in Home Improvement Stores now" Takes 7 coats to equal 2 coats of USA Paint and it just will Not Cure Properly and has a Terrible Tendency to slowly "Sag or Slide" overnight. After 1 & 1/2 weeks, even useing heat curing lamps 14 hours a day, the {China Enamel was like Bubble Gum and scraped off easily with your thumbnail!} Every single type of CHINA Paint we tried( and we tried MANY ), had an EXTREMELY Low Pigment amount in the paint. It has so Many Different Types of Thinners + Way Too Much Thinner in the paint that it Mists Terribly, causing it to FLOAT in the air worse than ANY spraypaint I have Ever used in my life, getting on Everything within 100 feet of the painting area. {"This is not an exaggeration"} Even their Laquer Paint from China will NOT cure properly, Sagging Badly Overnight. I have NEVER seen Laquer Paint do that before! I think that the Great amount of Different Thinners used & the Very low amount of Pigment in the paint is what causes it to not cure correctly and is what makes the paint Slide badly overnight. The Mellers Zinc Chromate Primer has a Very High amount of Yellow Pigment and Cures Hard in 48 hours so it can then be lightly sanded and finish painted. This makes the painting Job so much easier for you to do and gives you a much Tougher Paint when it is completely cured.
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YankDownUnder
Pro Diver
Broxton 'green label' Aqua Lung and 1954 USD Rene triple 44s.
Posts: 162
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Post by YankDownUnder on Oct 13, 2010 23:05:37 GMT -8
I recall the 90, but I know little about it, other than it was heavy. Many steel 72s were made by Walter Kidd for companies like US Divers. There were two other makers too. They came in round and toed bottoms. The toed bottoms meant they could stand up without a boot. Boots cause rust. Some were made with tapered threads, while others were made with a 1/2 inch parallel or 3/4 inch parallel thread. Some tanks were marked with the WP and a +, which meant they were safe to over fill by 10%. It is hard to put to get a twin set sometime, unless you can get them from the same maker. Even two round bottomed models might have a different profile on the base. So they are not all the same. Most of them were galvanized and those seem last forever. Some were lined with vinyl which needs to be removed, because it hides the rust when a VIP is done. It also caused the air to taste like plastic when they they were new, in the 1960's. Some USD 72s had vinyl on the outside, instead of zinc and they rusted so badly, you won't see many of them today. Some Healthways tanks had vinyl over the galvanizing which wasn't a great idea either. That was my first steel 72. I bought it in 1962.
The steel 72s with toes were intended by the maker, to be used as fire extinguishers. The Spanish company Nemrod (Seamless in the USA) bought those and marketed a good and distinctive product. Steve
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robohips77
Senior Diver
First Dives 1967. Never lost the fever.
Posts: 68
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Post by robohips77 on Oct 14, 2010 20:30:51 GMT -8
I distinctly remember being told it was "almost" impossible to get bent with a steel 72. Well, that is more or less true though there are quite a few people who could easily extend a dive with one long enough to get nicely bent. nem The Barlow effect. 12 dives on one steel 72.
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Post by Seahuntjerry on Nov 6, 2010 9:03:28 GMT -8
Some cow has a Rene 44 with Brownie decal on it. Moo Moo
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jon
Regular Diver
Posts: 26
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Post by jon on Jan 16, 2014 13:32:39 GMT -8
Great old thread. I too always understood the 72 sizing was to be compatable with the navy tables. It's interesting that the steel 72's held more air at 2250psi than an aluminun 80 with equal pressure. That fact,negative bouyancy,and compactness made them more desirable in remote places with aging compressors that didn't like 3000psi.
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Post by SeaRat on Jan 16, 2014 17:00:30 GMT -8
Jon,
This is a great thread. I have switched from my AL80s to 71.2 steel for my single tanks, as my AL80s need to be retired. They are the ones which have the potential for stress fractures in the threads. I find that the buoyancy characteristics of the steel 71.2 cubic foot tanks (actually about 68 cubic feet with a 2250 psig fill) is really nice, and allows very good diving without undue weight concerns that "modern" steel tanks have.
John
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Post by george on Jan 21, 2014 6:00:54 GMT -8
Have been using 72s for ever, I use a 100 HP with my other gear and its din, wish I had a aqua master so I could convert it to din and use my 100 HP. I have 72s that go back to the early 50s and still in use today! 72s are great tanks, now I need a double back pack so I go twins.
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