The Science Behind Cranes: Part 3, The Hydraulic Cylinder

In our first two editions, we briefly saw how cranes employ the simple machines known as levers and pulleys to maximize lifting capacity. Today's installment will cover the role of the hydraulic cylinder, and how it compares to the lever and pulley. Our next and final edition will review perhaps the most importance concept behind the physics of cranes, otherwise known as mechanical advantage.

Now, what exactly is a hydraulic cylinder? Well, simply put, a hydraulic cylinder is a cylinder, or a circular prism, that is completely filled with a fluid, most often an oil, that has two pistons. The pistons can be connected to the cylinder in a number of configurations.

Assuming each piston is the same size and weight and there is no friction, when something presses down on one of the pistons the other piston will move up at an equal force, speed, and distance. For example, if you press one piston down three inches, the second piston will shoot up three inches.

The greatest advantage to a hydraulic cylinder is that you may easily redirect forces from one plane to another. For example, one piston may be connected horizontally while the second may be positioned vertically. Levers and pulleys, as we saw before, do not translate direction this easily, and any force applied will result in a force on the same plane in the opposite direction. For example, moving a lever arm downward will move the opposite arm upward, and vice versa. However, the hydraulic cylinder will allow a force to be translated into a number of direction, such as up, down, forward, backward, left, or right.

On the other hand, the hydraulic cylinder can multiply forces by maximizing torque, as we saw with the lever and pulley. If one piston has an area of 6 square units, and another piston has a 2 square units, then the force pushing down on the smaller piston will appear 3 times greater on the larger piston. For example, if one pushes the 2-square-unit piston down with a force of 500 pounds, then the 6-square-unit piston receive a push with the force of 1500 pounds. However, the distance the larger piston moves will be 3 times less than the distance the smaller piston moved to create 1500 pounds of force.

Also similar to the lever and pulley, the hydraulic cylinder is used in almost all cranes. The cylinder may be applied directly to lift a heavy load, or it may aid another mechanism that directly lifts the load. A cylinder could be used in lever arms on cranes, or it may be used to move a jib or beam that acts as the lifting mechanism for the crane.

In conclusion, the hydraulic cylinder is much like the pulley and lever for its frequent use in cranes and its manipulation of torque. However, the hydraulic cylinder sets itself apart because of its ability to redirect forces to different planes. However, all three, the lever, pulley, and hydraulic cylinder, collectively maximize the mechanical advantage in lifting large objects. In the next installment, we will examine exactly what mechanical advantage is and how it's applied to cranes.

Serving in the crane industry for decades, Barnhart Crane and Rigging Companying provides the best in Crane Service andMachinery Moving.