HANDWHEEL OPERATORS AND TORQUE
What is torque?
Torque is a force tending to rotate a body about an axis.
(Example): force on a wrench tending to rotate a nut around a bolt.
How is Torque expressed?
Torque always has two parts, force and distance, and is expressed as the product of the two.
(Example): Torque = force x distance. Torque = pounds x feet. Torque = Newtons x meters.
Does that express Torque fully?
Well, not quite. Direction such as clockwise or counterclockwise must be included to express torque fully.
(Example): Torque = force x distance. Clockwise. Torque = lbft CW.
Why is Torque expressed as force x distance rather than distance times force?
Torque is expressed as force x distance to distinguish it from Energy which has the same units but is expressed as distance x force.
(Example): 100 lbft Torque. 100 ftlb Energy.
Valve Handwheel Torque and Rim Pull:
Valves are often operated by turning a Handwheel. Operating torque is applied by pulling on the Handwheel Rim. That’s called, Rim Pull. The amount of applied torque depends on the Rim Pull and the Handwheel size. Applied torque = Rim Pull x Handwheel center to Rim distance. Or Torque = Rim Pull x Half the Handwheel diameter. (Example): 80 lb Rim Pull on a 24 inch Handwheel: Torque = 80 lb x 24/2 in = 960 lbin or 960 lbin x ft/12 in = 80 lbft.
what is the most rim pull you can expect a person to apply to a handwheel?
360 N (80 lbf) can give the effort on common man
i think, Full the Handwheel diameter is needed, because we usually open&closed with two arms. isn’t it?
but usually a person open&closed both arms. isn’t it?
Nope! at site operations, the operator will most likely stand on one side of the valve and use both hands on the same spot on the handwheel and pull with both arms. This is true specially with larger size of valves with larger diameter handwheel.