How Hydraulic Machines Work?

Hydraulic machines are seen in almost all construction sites, heavy industrial activities and also seen in day-to-day activities. From a common hammer tool to the brakes in cars to the elevators and huge machines you see on construction sites, hydraulic machines are known for their amazing strength and agility. On any construction site you see hydraulically-operated machines like shovels, loaders, bulldozers, backhoes, fork lifts and cranes. Hydraulics mechanism is also seen in the control surfaces on any large airplane. Thus hydraulic machines have become very popular in today's technologically advanced world.

We all know that hydraulic mechanism implies that the force is applied using fluids unlike pneumatics where force is through gas. The big question is now how a hydraulic machine works using fluid as the main source of power?

How a hydraulic machine or system works?

The basic idea behind any hydraulic machine is very simple: An incompressible fluid is used to apply force at one point which is transferred to another point. The fluid is basically an oil, which needs to be checked regularly so that it is free from any contamination. The force is multiplied in the process. There are cylinders filled with oil and one piston is attached to each of them. The cylinders are connected to each other with an oil-filled pipe. If a downward force is applied to one piston, then the force is transferred to the second piston through the oil in the pipe. The movement of the piston is smooth since oil is incompressible. The best part of hydraulic systems is that the pipe connecting the two cylinders can be any shape, length and size.

An Example: The Clutch on Cars

In the clutch, there are two cylinders with a piston in each and a small tube running between them. When the clutch pedal is pressed, a force is produced which moves the piston on one of the cylinders (known as the master cylinder) pushing fluid under pressure into the other cylinder (slave cylinder). The fluid exerts pressure on the slave cylinder and produces a force which pushes on the clutch.

Here, the advantage of using hydraulic fluid is that it is very easy to add force which can further be multiplied. That is, if the piston on the right is 5 times larger than the piston on the left, the force applied to the left piston will appear 5 times greater on the right-hand piston. That is, if 100-pound downward force is applied to the left piston, a 500-pound upward force will appear on the right.

Clutch in Car

Mathematical Formula

The relationship between force and pressure is:
Force = Area x Pressure
That is
Pressure = Force / Area
So pressure is measured in units such as pounds (force) per square inch (area).