- Created on Monday, August 15 2011 09:03
- Written by Bill High, Founder, PSI-PCI, Inc.
A Brief Scuba Cylinder History
The first non-military scuba system arrived in the U.S.A. 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 1950's and early 1960's, several steel cylinder sizes were marketed having pressures ranging from 2,150 psig to 3,000 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 1980's, the DIN valve was introduced into the U.S. from Europe for use with cylinders rated above 3,000 psig. Only steel cylinders were authorized for commercial service until late 1971.
Most early commercial steel scuba cylinders ranged in volume from about 65 cuft to 95 cuft. However, many surplus World War II era 38 cuft cylinders with a service pressure of 1,800 psig were used, commonly as doubles. Some "38's" still pass their quality assurance tests and remain in service today.
The U.S. manufacturers of steel scuba cylinders included Pressed Steel Tank Co. (PST), Norris Industries, and Walter Kidde Co. The Italian firm Faber makes U.S. Department of Transportation (DOT) approved cylinders sold until recently under several brand names. Currently Faber cylinders are distributed by the Blue Steel Company. In the early 1990's, Heiser manufactured steel cylinders under the brand name Beauchat for sale in the U.S. Because of excessive weight, these cylinders were not popular. In 2004 Worthington, a Canadian company began distributing its steel cylinders under several brand names.
By the mid 1950's, PST and one other company began making aluminum cylinders from 6061 alloy for the U.S. Navy. The fabrication process was very different from the way aluminum cylinders are made today. Those round bottom aluminum cylinders are illegal for most purposes U.S. because they have no DOT designation. They must not be hydrostatic retested and not filled at commercial air stations.
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 are all aluminum scuba cylinders made today. In order to be equivalent to the then popular steel cylinders, Luxfer made its cylinder 6.8 inches in diameter to fit existing non-adjustable backpacks and with a similar 2,475 psig service pressure. To achieve the 72 cuft capacity, the Luxfer cylinder was made 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 1970's. The Kaiser cylinder (brand name AMF) has a 2,700 psig service pressure and a somewhat rounded (beveled) bottom.
Luxfer and Walter Kidde continued production under their 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 must 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 SP 6576 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 6061 alloy. Luxfer switched completely to the 6061 alloy by 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 1990's, Parker produced a few aluminum scuba cylinders.
PST created renewed interest in steel cylinders by introducing high-density 3,500 psig steel E9791 cylinders in 1987. Those cylinders were sold by Sherwood (Genesis) and U.S. Divers Co. (HP3.5). By 1998, that cylinder type was distributed in several volumes by other companies. In 2004 PST introduced an E series cylinder in both 2,400 psig and 3442 psig.
Coyne cylinders joined the steel scuba business in 1993, producing a limited number of 2,400 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 at the trade show. About 1990, two Russian titanium cylinders were demonstrated at the DEMA show. Their pressure rating exceeded 6,000 psig. However, because titanium cylinders 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 U.S. 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.