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Is there a difference in strength between one-piece-shaft and drive-shaft-and-trunnion design for butterfly valves?

QUESTION: Which is stronger, a one-piece-shaft or drive-shaft-and-trunnion design?

ANSWER: Multiple factors may affect a valve’s shaft strength, from material selection to shaft diameter, etc. Regarding the shaft design, if we take a closer look at one of the most widely used international standards for butterfly valves, API 609, it states the shaft-to-disc connection and all parts of the shaft within the pressure boundary will, under torsional load, exceed the strength of the shaft that lies outside the pressure boundary by more than 10 percent. This means the weakest point cannot be the disc-shaft connection area, where the actual difference between through shaft and drive shaft + trunnion design lies.

Our newest model, the Neles Neldisc versatile butterfly valve, complies with API 609, and both drive shaft + trunnion and through shaft design options are available. Both shaft design options come with the same high-level MAST (Maximum Allowable Shaft Torque) value. High MAST value indicates a high ability to withstand the load during the valve operation. Similarly, the reliability due to the extensive test-proven design and premium material selection is ensured for both options. This means that in terms of the endurance of the shaft solution, the user can benefit from high strength, high reliability and long maintenance intervals with either of the shaft options, even for most demanding services.

QUESTION: Does the performance of the valve change depending on the selected shaft option?

ANSWER: An optimized disc design and unique backflash-free pinned disc-shaft connection provide long-lasting performance and precise flow control for both shaft constructions. Precise control minimizes unnecessary pressure fluctuations and repetitive readjustments, resulting in energy savings.

Furthermore, the drive shaft + trunnion design of our newest model versatile butterfly valve leaves even more free space in the middle of the valve flow port. This enables our newest model, the Neles Neldisc versatile butterfly valve, to have a market-leading flow capacity, leading to increased plant efficiency and optimized valve size in the control service.

Vincent Wang
Product Manager, Butterfly Valves
FC P&S Product Lines VEQ
Butterfly Valves