Feuil1I have a Double Acting Actuator originally sized for a 4" 900# Full Port Ball Valve.I need to know if this Actuator could be used for a 3" 1500# Full Port Ball Valve.I need to use this 3" 1500# Ball Valve in a max 2000 psig/100F application.There will be a By-Pass in the line to balance upstream and downstream pressure when the Valve is actuated.Does anyone know how to make this type of calculation?Or do I need more information?Response 1:You need to establish the manufacturer and model number of the actuator and then contact them for the torque details relative to the input pressure.Once you know the torque output of your actuator you can compare this to the torque requirement for your new valve.Bear in mind that you need to add at least 25% to the valve torque to cover for performance degradation over its operating life relative to the torque output of the actuatorResponse 2:The formula has many variables that vary from vendor to vendor but also even many power plants have their own values for several variables in the formula:

Thrust (lbs) =[StA]*[LP] + [PL] + [SA]*[VF]*[DP]

StA = STem cross sectional AreaLP = Line PressurePL = Packing Load. This is a value that will vary vendor to vendor and is dependent on valve size. Typically we use values from 1000 lbs to 4000 lbs depending on valve size and pressure classSA = Seat AreaDP = Differential Pressure the valve is opening/closing againstVF = VALVE FACTOR. This is the most controversial subject around gate valves. Generically a 5 wedge gate valve uses a 0.3 factor however you will have many Nuclear power plants that argue for anywhere from 0.4 to 0.6 for this value depending on service. If you use a steeper wedge like 3 or less their is a strong argument that this value should be even higher. For parallel slide valves we typically use a 0.2 however I have never seen any consensus on this value.We have been using it for years and haven't had a problem with undersized operators so it seems to work for us.Torque (ft-lbs) = [Thrust] * [SF]SF = STEM FACTOR, this is dependent on the type of stem threads you use. Be aware that there is some disagreement also on stem factor calculations in the industry also. Many stem factor calculations will use a coefficient of friction of 0.15 while many power plants (and also myself) think this is too small and a 0.20 COF should be used whencalculating stem factor.These formulas get you a baseline torque and thrust value with no safety factor. You'll need to add an appropriate safety factor for your service

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