Ball valves torque is determined by the seat material, the ball material, the process fluid lubricating (or fouling) the seats, the pressure differential loading the ball against the seat, the design of the seats Bellows Seal Valves(some seats are preloaded for application reasons but this causes higher torque). As he suggested, all these factors are considered in the manufacturers' torque tables. SomeCheck Valves manufacturers also publish a liat of safety factors for actuator sizing....if the valve sits two weeks between actuation, it will take a set and need a mighty heave to make it start moving. You did not specify Plug Valves ball valves in your question, though. Butterfly valves also have torque consideretions: Type of valve, seat material, process fluid velocity and density, packing material all affect the Safety Valves torque required. Again, there is no national standard and there is much variation between similar valves from different nmanufacturers. Consult the manufacturer's literature. All above mentioned Safety Relief Valves factors account for the torque. But, I would like to say sometimes, manuafacturers just copy and modify the torque with similar design and functions of other competitors. Of course, they include the safety factor to over-estimate the torque value, and in turn, larger size of actuators are used instead. So, they can earn more money. For some good one, they will measure the torque or send them to laboratory during the prototype testing.

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