Damper Torque Requirements

[simar187]

I am trying to determine the torque requirements of butterfly style dampers for air service. The dampers will be eccentric and range in size from 24" to 84" in diameter. Furthermore, they will be custom fabricated and NOT cast. The torques I am considering are Seating, Packing, Dynamic and Hydrostatic.
I have used torque sizing formulas from AWWA for butterfly valves, but they appear to be producing torques that are much too high. The hydrostatic torque, Th, which applies from the difference in static head of water on the valve disc above and below the valve shaft when the shaft is horizontal, is what the torque which is inflating my results since me dampers are for gas service. The formulas used follow:

Seating or Unseating Torque, Ts
Ts = Cs D2
where, D, damper diameter, ft
Cs, coefficient of seating or unseating torque

Bearing Torque, Tb
Tb = 4.71 D2 d f ?P
where, D, damper diameter, feet
d, shaft diameter, inches
?P, pressure drop across damper, PSI
f, bearing friction coefficient (0.25 for metal bearings)

Dynamic Torque, Td
Applies when damper is just open , 5 deg < ? ? 90 deg
Td = Ct D3 ?P
where, Ct, coefficient of dynamic torque
D, damper diameter, feet
?P, pressure drop across damper, PSI

Hydrostatic Torque, Th
Th = 3.06 D4
where, D, damper diameter, feet

Required Actuator Torque, Ta
Ta1 = Tb+Ts+Th
Ta2 = 1.2Tb+Td
Ta = max (Ta1, Ta2)

Any insights on how to adequately size for an actuator would be greatly appreciated.

Thanks, Simar

 

[simar187]

In my above post, ?P is suppose to be delta P, the pressure differential, wherever used.
Under dynamic torque, where it specifies:
5 deg < ? ? 90 deg
It's suppose to be 5 degrees < alpha , 90 degrees, where alpha is the angle of disc opening.

Simar