Figure "I" shown in the illustration is a diagram of a valve hand wheel, with S=8 inches and T=50 lbs. When an 24 inch cheater bar is used instead, and V=50 lbs., as shown in Figure "II", what value of additional torque is now being applied to the hand wheel valve stem? See illustration GS-0109.
• Use the torque formula: Torque = Force × Distance from the center (moment arm). • Compare the original radius (S = 8 inches) of the hand wheel to the new effective radius when a 24-inch cheater bar is added. • Distinguish between total torque with the bar and the extra (additional) torque compared to the original setup.
• First calculate the original torque on the valve stem using the given force and wheel radius. What number do you get in inch-pounds? • Next, determine the new total distance from the stem to where the 50 lb force is applied when using the cheater bar. Then compute the new torque. • Finally, compare the new torque to the original torque: how much more torque (not the total) is being applied? Is it 1, 3, 4, or 5 times the original?:
• Be sure you are using the distance from the valve stem to the point of applied force, not the diameter of the hand wheel. • Verify that you find the total radius with the cheater bar (hand wheel radius plus bar length). • Double-check that you’re choosing the factor that represents the increase in torque over the original, not the total torque itself.
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