Source of Torque on Butterfly Valves

[aggieengineerrmb]

Does anyone know what design factors most affect the operating torque of a butterfly valve. I am talking about same size and configuration of valves here. There was some thought in our group that the stem bushings were the significant component, however tests using alternative friction reducing coatings as a way to lower operational torque have proven ineffective so our thought is that the friction between the bushings and the seat is only a minor contributor to the operating torque of the valve.

 

[BRIS]

The valve spindle is usually not in the centre of the disc and hence the valve is not hydraulically balanced. If the valve is installed with the spindle axes on the upstream side of the disc the valve will attempt to close under flow. If it is installed with the spindle axes downstream of the disc it will attempt to open. The torque is a function of the geometry and the flow rate. At high flow friction is only a minor contributor

brian