Does anyone know of a calculation or 'rule of thumb' process for determining the breakaway torque of a ball valve? I am designing a class 1500 ball valve from scratch and am using ASME B16.34 2009 for body bolts, wall thickness and general design, but there seems to be nothing on stem sizing. I need to know what torque I will be applying to the stem in order to determine the stem diameter.I believe it must be a function of the presure acting on the ball, thereby pushing it into the seat and the resultant rotational friction to overcome this force.The ball valve would be floating as it is in the size range up to 2". The posts indicated seem to show torque values for existing ball valves from different manufacturers. I am trying to determine how the stem is sized when starting with a blank sheet. My experience as a newbie to the valve industry (originally a burner designer) is that a lot of data is merely copied from leading manufacturers and I myself had problems when designing burners with eroneous valve Cv values etc. from some of the smaller manufacturers.I assume that there must be a way to size the stem given the pressure (B16.5 ratings) and seat material. Being a floating ball valve there may be an element of pre-loading (clamping of seats), but this would increase significantly when 3000psi pressure is applied. I fail to see how a valve can be designed without firstly determining the expected torque to be overcome by the stem.

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