The Intriguing Story of the Pressure Seal Valve(1)

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.”

This Powell pressure-seal fixture dates back to 1938, when the company began its first pressure-seal valve experiments

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.

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.

This 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

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 Intriguing Story of the Pressure Seal Valve(1)

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