A Brief Scuba Cylinder History
By Bill High, PSI, Inc., NAUI #175

The first non-military scuba system arrived in the USA in 1949. Within months, a small group of scuba divers emerged from among geology, oceanography, and biology students at Scripps Institute of Oceanography, La Jolla, California.

Throughout the 1950s and early 1960s, several steel cylinder sizes were marketed having pressures ranging from 2150 psig to 3000 psig. Between 1958 and 1960, valves changed from mostly 1/2 inch tapered thread to 3/4 inch, 14 turns to the inch, straight thread with O-ring. However, there were some 1/2 inch straight threaded cylinders as well. In the late 1980s, the DIN valve was introduced into the US from Europe for use with cylinders rated above 3000 psig. Only steel cylinders were authorized for commercial service until late 1971.

Most early commercial steel scuba cylinders ranged in volume capacity from about 65 cu.ft. to 95 cu.ft. cylinders with a service pressure of 1800 psig were used, commonly as doubles. Some "38s" still pass their quality assurance tests and remain in service today.

The US manufacturers of steel scuba cylinders included Pressed Steel Tank Co. (PST), Norris Industries, and Walter Kidde Co. the Italian firm Faber makes US, Department of Transportation (DOT) approved cylinders sold by the brand names Scubapro and OMS. Other US distributors of approved Faber cylinders have emerged since the summer of 1998. In the early 1990s, Heiser manufactured steel cylinders with several volumes un the brand name Beauchat for sale in the US. Because of excessive weight, these cylinders were not popular.

By the mid 1950s, PST and perhaps one other company began making aluminum, cylinders from 6061 alloy for the US Navy. The fabrication process was very different from the way aluminum cylinders are made today. Although many of those round bottom aluminum cylinders found their way into civilian service, they are illegal for most purposes because they have no DOT designation. Those cylinders must not be hydrostatic retested and should not be filled at commercial air stations. WARNING-there are no legal round or semi-round aluminum scuba cylinders. Even though many of the old US Navy and Kaiser (SP6576) cylinders are used today, they are illegally retested by careless retesters and filled by unknowing fill station operators.

Newly formed Luxfer USA Ltd, (in 1997 the company name was changed to Luxfer Gas Cylinders), with DOT special permit SP6498, began producing aluminum cylinders in late 1971. Using 6351 alloy in a cold extrusion process, the cylinder did not require a bottom plug as did the former military type. The Luxfer approved cylinder had a flat bottom, as must all approved aluminum scuba cylinders. In order to be equivalent to the then popular steel cylinders, Luxfer made its cylinder 6.8 inches in diameter to fit existing nonadjustable backpacks and with a similar 2475 psig service pressure. To achieve the 72 cu.ft. capacity, the Luxfer cylinder was longer but, as a consequence, it was about 11 pounds buoyant when near empty. Divers quickly named it the "floater".

Walter Kidde (with special permit SP7042), Norris Industries (SP6688), and Kaiser (SP6576) followed Luxfer into the aluminum cylinder business during the early 1970s. The Kaiser cylinder (brand name AMF) has a 2700 psig service pressure and a somewhat rounded (beveled) bottom.

Luxfer and Walter Kidde continued production under the DOT SP6498, E6498 or SP7042. E7042 until the DOT formalized the aluminum cylinder category 3AL in July 1982. Unfortunately for owners of Norris Industries SP6688 and Kaiser SP6576, BOTH CYLINDERS should be removed from service in the US as those permits expired by 1979. A special grandfather clause allows their use in Canada. Like the illegal navy surplus aluminum cylinders, many SP6688 and SP6576 cylinders are used in the US because hydro retesters, fill station operators, and owners ignore or are ignorant of their status.

The Catalina Tank Co (now called Catalina Cylinders) began manufacturing 3AL cylinders in 1986 using the 6061 navy cylinder alloy. Luxfer switched completely to the 6061 alloy for June 1988. while Walter Kidde continued using alloy 6351 until production ceased in July 1989. today, only Luxfer Gas Cylinders and Catalina Cylinders produce 3Al scuba cylinders for sale in the US and much of the world. In the early 1990s. Parker produced a few aluminum scuba cylinders.

PST created renewed interest in steel cylinders by introducing high-density 3500 psig steel E9791 cylinders in 1987. Those cylinders were sold by Sherwood (Genesis) and US Divers Co (HP3.5). US Divers held a sales exclusive for this cylinder during 1997. By 1998, that cylinder type was distributed in several volumes by other companies.

Coyne cylinders joined the steel scuba business in 1993, producing a limited number of 2400 psig cylinders in several sizes. Coyne, a subsidiary of Taylor-Wharton is not manufacturing scuba cylinders in 2001.

Two other cylinder types attracted much interest in the diving community. About 1986, Dacor demonstrated a stainless steel scuba cylinder at the DEMA trade show. It was an attractive cylinder that boasted many advantages over other metals. However, no DOT approved cylinders were ever produced, including the models shown a the trade show. About 1990, two Russian titanium cylinders were demonstrated at the DEMA show. Their pressure rating exceeded 6000 psig. However, because titanium cylinder require welding, DOT approval was difficult to acquire as high-pressure DOT cylinders must be seamless. Titanium cylinders are now produced in Russia and sold by a US company to international military units. Although heavier than common scuba cylinders, those cylinders have exceptional capacity when compressors are available to achieve the high rated pressure.

Sources - January/February 2002 copyright 1996 NAUI. All rights reserved.

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