The gear coupling was the primary flexible coupling for industrial gas turbines for almost twenty-five years. As advancements in the industrial gas turbine have occurred so have advancements in gear couplings. There are many variables in gear couplings that can affect their characteristics, including tooth design, materials, and lubrication methods. All couplings react on connected equipment. The system designer must consider these reactions when designing the system. If a gear coupling is chosen, there are many characteristics which can make a designer’s life easier. This paper compares the characteristics of diaphragm couplings versus gear type couplings used in industrial gas turbine applications including applications of couplings for turbine to generator, turbine to mechanical drives (compressors, pumps, and gear) and also couplings used between the turbine and accessory gears. The methods used to analyze the design and the forces and moments generated by both the gear coupling and the diaphragm coupling are also provided. These analysis are used to show that the forces and moments generated by a diaphragm coupling are not only predictable, but usually lower than those of a gear coupling. The paper shows that a diaphragm coupling can be more predictable and reliable than a gear coupling for most industrial gas turbine applications.

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