Fluid Power Journal

Problem: Standard Size Cylinder

The figure shows a door to open with an air cylinder pushing at a 45-degree angle. The door is 48 inches high and weighs 100 pounds. It needs to open 90 degrees with a 12-inch stroke cylinder using 100 psi of air pressure. The door is uniformly balanced. What standard size cylinder is needed to open the door?

Find Out The Solution
There are several ways to solve the force needed to lift the door.The formula is force x force distance = effort x effort distance. This is a moment equation, and the forces must be calculated perpendicular to the distance. The center of gravity for the door is 24″ from the hinge. Therefore, 100# x 24″ = 8.49 x the effort. Effort pushing straight up at the cylinder rod is then 282.69 lbs. Now divide that answer by the sine of 45 degrees, and you will get an effort of 400 lbs.A second way is to determine the minimum perpendicular distance that the cylinder will see from the hinge. Take the 8.49″and multiply by the sine of 45 degrees, and you will get 6 inches. That distance is also equal to 1/2 the distance of the stroke that was listed as 12″. Now the moment equation is 100 lbs. x 24″ = 6″ x effort. Effort again equals 400 lbs.

Given is the pressure at 100 psi. Use F = PA. Force / Pressure = Area. 400 / 100 = 4 square inches. Use A = D x D x 0.7854 and work backwards. Four / 0.7854 = square root = 2.26″ diameter. The next standard size cylinder is 2-1/2” bore. That will allow the pressure to be reduced to 82 psi, allowing for any lost for friction, etc.

Final answer is 2-1/2″.


Deadline past. Not available for submissions.

Winning Answer Submitted By:

David Motley, CFPS, Parker Hannifin Corp., Kings Mountain, NC

Correct Submissions By:

George Fling, CFPS, Southwestern Controls, Dallas, TX

Ronald Arreola, CFPS, Hydraforce, Inc., Lincolnshire, IL

Joseph Entwistle, CFPE, Hydro Air Dees, Point Pleasant Beach, NJ

Paul Connop, Sunsource

By Ernie Parker, AI, AJPP, AJPPCC, S, MT, MM, MIH, MIP, MMH,
Fluid Power Instructor, Hennepin Technical College, EParker@Hennepintech.edu

This teaser is printed in the Fluid Power Journal. Submit your answer HERE. Those who submit the correct answer before the deadline will have their names printed in the Society Page newsletter and in Fluid Power Journal. The winners will also be entered into a drawing for a special gift.

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