Hydraulic Cylinders: How They Work

Want to know about hydraulic cylinders? How they work together as a system? Ever wondered, when a airplane is coming in to land on the runway, which of the pilots goes and pushes out those huge wheels that are snuggled tightly in the belly of the airplane. Well, nobody has to move from his seat to do so, all a pilot has to do is push a button to activate hydraulic system of the landing gears to set the wheels out as a preparation for landing. This system primarily, consists of the cylinders, connecting pipes in one or other forms, shape and hydraulic liquid. The basic fact that enables a hydraulic system to work is that, the force, when applied at one place or point in it, is transmitted to another place or point through the use of an incompressible fluid such as oil.

Working of Hydraulic Cylinders

During the course of the work like any other mechanical objects, hydraulic systems wears out. The cylinders are its main component and knowing how to rebuild hydraulic cylinders, after dissembling and repairing them comes useful. The most basic example that can be thought of to understand them and how they work together is as follows.

Two cylinders of different diameter are connected with the help of a pipe. The cylinders stand parallel to each other and right angle to the pipe. This 'U' assembly is then filled with oil such that the cylinders are partly filled. The open end of the cylinders facilitates for 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 right angle to the disc. The other end of the piston rod sticks out of the open end of the cylinders.

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-inches in diameter (3-inches radius). When the 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 (Pi x r²) 3.14 and that of the big piston is 28.26 (9 x 3.14). Because of the difference in the area of the pistons, any movement (which in itself needs force) of the small piston exerts 9 times greater force on the large piston enabling it to move. If we apply 100 pounds of downward force on the small piston, we get 900 pounds of force on the big piston. If we want to displace or lift it, say, by 1-inch then, we have to move small piston downward by 9-inches.

The hydraulic cylinders dispenses the need of rigid structure to transfer the force between two points or surfaces. This fact is used to make hydraulic systems with numbers of twists and turns in them, but still effectively delivers required force, with minimum loss, at the intended point. There are occasions, when we cannot use rigidly connected system 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 Cylinder's Parts

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

Types of Hydraulic Cylinders

In practice, two main types are used heavily: the tie rod cylinder and the welded body cylinder. The tie rod cylinder is 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.

Their design enables them to produce force that can only be used for pulling and pushing. Its drawback is that it cannot provide for bending movements or support the side loads. This was all about the hydraulic cylinders for any enthusiast of mechanical things.