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Valve Techbook 2017

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Page 8 of 35 | September 2017 | 7 VALVE TECHBOOK: TECHNOLOGY "SPM valves have an open center and are two- position [open and close] and are three-way [work port, pressure port and tank port]," he explained. After researching how the valves work, NOV dis- covered that the opening and closing of the valves is what causes the shock in subsea BOP systems. "That shock is not a function of opening fluid to a piston or something like that. The reason you get this shock is because of the open-center con- figuration. Pressure is actually venting to the tank. The short burst and sudden stop of pressure creates the shock in the system," Springett said. After instrumenting a system to see how every- thing works, the company took a look at the valve itself, including the design of the spool and cage. "We designed a system that was a closed-center valve. What that means is that as the valve is tran- sitioned all ports are not open to each other. It was pretty remarkable how we were able to virtually eliminate the shock in the system," he continued. "The big plus to that is BOP reliability. One of the big pieces of BOP reliability is hoses, piping and tubing. By eliminating the shock that we pro- duced from the fundamentals of a conventional, old-school SPM valve, we not only impact the reli- ability of the valve because we don't have the shock associated with it, but we also impact the reliability of the entire system since it increases the life of all the components that hydraulic fluid comes in contact with such as pressure regulators, shuttle valves, piping, etc.," Springett emphasized. On the stream side of the valve, NOV saw high shock loads, and the SPM valve is right next to the regulators. Shuttle valves were also affected by the shock. "We confirmed that eliminating the shock was a really, really important aspect in robustness and reliability," he added. "We could have stopped a eliminating the shock in the system but we didn't. We looked at every aspect of the valve and designed around reliability. "We redesigned the seals to handle large extru- sion gaps. We can rework the valve pockets in the field, which allowed us to fundamentally redesign the pod to eliminate leak paths. We eliminated troublesome fasteners from the design and uti- lized and placed wear bands that are more tolerant to contamination. We designed components symmetrically so parts can't be installed back- wards or upside down. The list goes on and on," Springett said. For existing systems, the valve block is changed and the new one is bolted in. There are no funda- mental changes to the control system, he added. "When our engineers are looking at designing for robustness and reliability, the first question is not, 'How do I make that item more reliable?' Their first question is 'How can I eliminate that item?' This is the essence of the design philosophy of the Low Shock SPM valves," he said. Remote partial stroke testing Safety in today's hazardous process piping envi- ronment is critical. "At Emerson we want to do our part to make sure our customers who work in these plants go home safe to their families at the end of the workday," said Shawn Statham, global prod- uct manager—actuated safety systems for Emerson Automation Solutions. "We're a manufacturer, yes, but we want to come together with the people who operate these offshore platforms and production facilities and partner with them to develop more reliable and safer solutions. "Safety shutdown systems (SSDS), or safety instrumented systems (SIS) to be specific, continue to be a significant area of focus around the world. SSDS provide an additional layer of safety that help to protect personnel, the environment, and assets, etc.," he continued. Over the last 20 years the industry has seen a NOV discovered that the opening and closing of the SPM valves caused the shock in subsea BOP systems. By designing a closed-center valve system, the company was able to virtually eliminate shock. (Photo courtesy of NOV)

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