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.