How Does a Hydraulic Cylinder Work?

When an airplane is coming in to land on the runway, have you ever wondered how those huge wheels, that are snuggled tightly in the belly of the airplane, are deployed? Well, all a pilot has to do is push a button to activate the hydraulic system of the landing gear, to set the wheels out as a preparation for landing.

This hydraulic system consists of cylinders, connecting pipes, and hydraulic liquid. The basic fact that enables a hydraulic system to work is that, the force, when applied at one place or point, is transmitted to another place or point through the use of an incompressible fluid, such as oil.

Two cylinders of different diameters are connected with the help of a pipe. The cylinders stand parallel to each other and at a right angle to the pipe. This assembly is then filled with oil, such that the cylinders are partly filled. The open end of the cylinders facilitate the manipulation of pistons in them.

One can imagine a piston as a flat solid disc which has a piston rod attached at its center, such that it stands at a right angle to the disc. The other end of the piston rod sticks out of the open end of the cylinder.

The piston of the small cylinder, say, is of 2-inch diameter (1-inch radius) and that of the big cylinder, say, is of 6-inch diameter (3-inches radius). When force is applied to the small piston, it tries to compress the oil in the small cylinder.

But oil is incompressible, and the force is then transmitted through it to the disc of the big piston, and moves it upward in its cylinder. The area of the small piston is 3.14 (pi × r²), and that of the big piston is 28.26 (pi × r²).

Because of the difference in the area of the pistons, any movement of the small piston exerts 9 times greater force on the large piston. If we apply 100 pounds of downward force on the small piston, we get 900 pounds of force on the big piston.

Hydraulic cylinders dispense the need of a rigid structure to transfer the force between two points or surfaces. This fact is used to make hydraulic systems with a number of twists and turns in them, but still effectively deliver the required force, with minimum loss, to the intended point.

There are occasions when we cannot use rigid systems, and hydraulic systems are used in such conditions. By increasing the length of the small cylinder and increasing the radius or the diameter of the big piston, we can design a hydraulic system to push, pull, or lift heavy weights.

Hydraulic cylinders that are used in real life applications are not as simple as described above. For anyone interested in its parts, a list is presented below:

• Cylinder barrel
• Cylinder bottom (Cap)
• Cylinder head
• Piston
• Piston rod
• Rod glands
• Cylinder bottom connection
• Seals
• Cushions

In practice, two main types are used heavily: tie rod cylinders and welded body cylinders. Tie rod cylinders are used for heavy-duty industrial use. They come as small-bore as well as large-bore cylinders. The other type of cylinder, i.e., welded body cylinder has no steel rods in it.

The top end of the cylinder barrel is welded to the object that it is designed and constructed to move. This cylinder is small in size, and mostly found in smaller machines. Telescoping hydraulic cylinder is a special type of cylinder in which the piston rod retracts into the cylinder barrel.