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  • #592

    Engineer
    Participant

    Hello,

    Please could you give me the formula for working out force put on motor, regarding motorised valves… in N?

    #598

    ValveGeek
    Member

    Dear Sir or Madam
    Thank you very much for your question.
    The force that an actuator has to develop to manoeuvre or close a globe valve has several components:
    • Primarily, the actuator has to act against the hydrostatic forces exerted by the fluid onto the plug. The simple formula for this is cross section of the plug (or seat) * differential pressure
    • The second force that it has to fight is the packing friction. This is generally a coefficient (depending on the packing material and stem surface) * stem diameter
    • The third force (only taken into account for closing, not manoeuvring) is the seating force, which will also generally be a coefficient * seat diameter.

    Obviously, this does not apply as is if the valve has a balanced trim, double seat or anything along these lines.
    The “seating coefficients” and “packing friction coefficients” will be specific to each manufacturer and depend on the sealing surfaces materials and leakage rate class required. The hydrostatic force is pretty straight forward to determine and will give you an idea of the order of magnitude of the actuator size.
    I hope this helps, any further questions please contact us.
    Valvegeek

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