A History of Valves

The Intriguing Story of the Pressure Seal Valve

In a quest for more efficient power generation, power plants in the 1930s continued pushing the pressure-temperature envelope. For piping component manufacturers, that meant requirements kept increasing and designs needed to be brought up to date. Classes 900 and 1500 surpassed the Class 600, once deemed “very high-pressure.”

For the valve manufacturer, building the large bolted bonnet high-pressure valves required for the new levels of power was not difficult; however, the new designs required large quantities of metal in the large castings to accommodate the large body/bonnet flanges. Also, gasket leakage cases were increasing because of bolt relaxation as well as the limited amount of fastener research available at the time.

Some valve manufacturers began to experiment with a welded bonnet design for various sizes of valves that relied on a mechanical connection to handle the greatest amount of pressure load. The connection worked in conjunction with a pressure-containing seal-weld to keep the joint from leaking. The technology was sound; however, repair and maintenance on these large valves was costly and difficult.

Hobbs-patentThis is the original Hobbs patent filed in February of 1940. Although Hobbs would lose a lawsuit based upon this patent, he would be successful in legal actions involving other valve design patent infringements.The perfect solution would be a gasket seal that became tighter as the internal pressure increased. This innovative sealing concept had been used in high-pressure research, but it had not yet been applied to valve production. The heart of the seal in this case used a tapered ring of soft steel wedging against the side of the pressure vessel body. However, a prolific mechanical engineer by the name of James C. Hobbs tried to single-handedly change the situation.

Hobbs approached several U.S. manufacturers to offer to license “his” pressure seal valve design. The valve companies could see the benefit of building these “pressure-sealed” valves, so they were all ears to the sales pitch. Several manufacturers cooperated with Hobbs and gave him a royalty percentage. There was one manufacturer from Cincinnati, Ohio, however, that did not listen to Hobb’s sales appeals.


The Cincinnati firm was working with an inventor from Germany named Kurt Bredtschneider, who patented a pressure-seal joint in 1932. Working with Bredtschneider, The William Powell Company proceeded to build an order of pressure-seal-designed valves for Diamond Alkali and for Wisconsin Power and Light. The products were installed in 1939.

At about the same time, information surfaced about another European inventor, Friedrich Uhde, who designed and built a pressure seal valve sold to Universal Oil Products in 1935 for use in a high-pressure autoclave. Because of all this, as the storm clouds of World War II began to gather, the claim to the pressure-seal design was also getting more and more cloudy.

Another stalwart U.S. manufacturer, Crane, designed and built pressure sealed valves installed in a monitored high-pressure boiler, which operated throughout the war. Because the War Production Board regulated wartime valve construction activities, the pressure seal design issue took a backseat to other priorities. However, as soon as hostilities stopped, the rush to product development was on again.


As part of the spoils of war, the United States instituted “Operation Paperclip,” a harvesting of as much German engineering knowledge as possible. Results of this dragnet included Dr. Werner Von Braun, who jump-started the U.S. missile and space program. Another interesting catch for the paperclip collections was a physics expert by the name of Kurt Bredtschneider—the same Bredtschneider who tried to offer his pressure-seal technology to the U.S. industry eight years before. As part of his post-war agreement with the United States government, the esteemed physics professor had only two requests: “that his sister be allowed to immigrate to the U.S. and that he have all the coffee that he could drink.”

Crane-pressure-seal-ad-1952A 1952 Crane ad promises “a radically new idea in valve design,” an idea that was based upon design principles that were a quarter century old.After the U.S. government got the information they wanted from Bredtschneider, the professor began to pursue his previous pressure-seal venture within the U.S. valve industry. He was a guest of Crane, where he was shown the “newest” (it was 1945) pressure-seal design they possessed. After examining the product, Bredtschneider was quoted saying, “If you are using my design, the least you could do is use it right!” Apparently Crane agreed because they hired him, and he became a valuable part of the Crane engineering department for the next 15 years.


As the 1940s ended and the 1950s began, some of the Hobbs licensees stopped paying him royalties. This obviously did not sit well with Hobbs who had no desire to take a vacation from engineering design work and what it paid. Hobbs resorted to a lawsuit against Wisconsin Power & Light and Powell. The lawsuit was initially won by Hobbs; however it was eventually overturned by the Court of Appeals for the Seventh Circuit in 1957. The case is now famous and is referenced often in the field of patent law.

Chapman-large-OD-welded-bonnet-valve-adPrior to the introduction of pressure-seal technology for valves, several manufacturers provided welded bonnet valve designs in all size ranges to eliminate any gasket seal flow path. This design worked well, but resulted in large valves that were very difficult and expensive to repair and maintain.What transpired from the proceedings was that Hobbs had no right to the technology because it was in the public domain at the time of his involvement. The technology had in fact been perfected by Dr. Percy W. Bridgman from 1905 to 1908. Bridgman developed the seal by necessity as an adjunct to his ultra-high-pressure research. He detailed his joint in his book, The Physics of High Pressure, published in 1931. The pressure-seal joint he developed as applied to pressure vessels and pipe connections was referred to as the “Bridgman Joint” as late as the 1950s and 1960s.


The pressure seal valve was truly a problem-solver for the high-pressure steam industry. It was the perfect technological match for the welding expertise that now made excellent, high-integrity butt-weld ends commonplace.

Up until this time, valve design and pressure ratings were derived from the existing flange standards, primarily the American Society of Mechanical Engineers (ASME) B16.5, Pipe Flanges and Flanged Fittings. Since the pressure seal valves had no body/bonnet flanges, a new standard for pressure temperature ratings was needed. This standard was developed by the Manufacturers Standardization Society as SP-66, Design and Ratings of Steel Butt-weld End Valves, in 1964. It would serve as the design standard for pressure seal valves until the development of ASME B16.34, Valves‒Flanged Threaded and Welding End, in 1974.

Today, pressure seal valves are manufactured of low carbon steel, chrome/ moly and austenitic stainless steel in pressure classes up to 4500. Pressure seal design today is fairly standardized by manufacturers all over the world. This current calm attitude of universal pressure seal design acceptance is a far cry from the battles waged in the power houses and court houses of 50 years ago…all over a tapered ring of soft steel.

Greg Johnson is president of United Valve (www.unitedvalve.com), Houston, and is a contributing editor to VALVE Magazine. He serves as chairman of VMA’s Education & Training Committee, is a member of the VMA Communications Committee and is president of the Manufacturers Standardization Society. Reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..