Working principle of Hydraulic machines

Definition

A hydraulic machine is a mechanical device that operates by using the pressure energy of an incompressible fluid to transmit, control, and multiply force.

In simple terms, when pressure is applied to a liquid inside a closed system, that pressure acts throughout the fluid and can be used to do useful work such as lifting, pressing, braking, or moving heavy objects.

Main Content

1. Pascal’s Law

• Pascal’s law states that when pressure is applied to a confined fluid, the pressure is transmitted equally and undiminished in all directions throughout the fluid and to the walls of the container.
• This is the basic scientific principle behind all hydraulic machines. Because liquids are nearly incompressible, a force applied on a small area can produce a much larger force on a larger area.
• For example, if a small piston is used to apply pressure to a fluid, the same pressure reaches a larger piston, and the larger piston produces a greater output force.

2. Pressure, Force, and Area Relationship

• The working of hydraulic machines depends on the relation: Pressure = Force / Area. This means that for the same pressure, a larger piston area gives a larger force.
• In a hydraulic system, a small force acting on a small piston creates pressure in the fluid. That pressure is transferred to another piston with a larger area, resulting in force multiplication.
• For example, if the input piston area is 2 cm² and the output piston area is 20 cm², then the output force becomes 10 times the input force, provided the pressure is the same.

3. Force Multiplication and Mechanical Advantage

• Hydraulic machines are designed to multiply force, which is known as mechanical advantage. This allows a person or motor to move or lift very heavy loads with little effort.
• The output force depends on the ratio of the piston areas. A larger area ratio gives a greater mechanical advantage.
• For example, a hydraulic jack used in automobile workshops can lift a car by applying a small force on a hand lever, which creates pressure and lifts the vehicle through a large piston.

Working / Process

1. Input force is applied to the small piston

• A person, pump, or motor applies force on a small-area piston or plunger in the hydraulic system.
• This force increases the pressure of the liquid inside the closed cylinder.

2. Pressure is transmitted through the fluid

• According to Pascal’s law, the pressure produced in the confined liquid spreads equally throughout the system.
• The fluid carries this pressure without significant loss because it is incompressible.

3. Output piston moves and produces larger force

• The transmitted pressure acts on a larger-area piston, producing a much greater force.
• This larger force is used to lift, press, brake, or move an object. When the input force is removed, the system can return to its original position using valves, springs, gravity, or pump action, depending on the machine.

Advantages / Applications

Force multiplication

• Small input force can lift or move very heavy loads, making hydraulic machines highly efficient for heavy-duty work.

Smooth and controlled operation

• Hydraulic systems provide steady motion, accurate control, and shock-free force transmission, which is useful in brakes, lifts, and industrial presses.

Wide applications

• They are used in hydraulic jacks, hydraulic brakes, cranes, excavators, presses, aeroplane control systems, and many manufacturing machines.

Summary

• Hydraulic machines work on the principle that pressure applied to a confined fluid is transmitted equally in all directions.
• They convert small input force into a large output force by using pistons of different areas.

• Their main importance is in lifting, pressing, braking, and other heavy-duty applications.

• Important terms to remember

• Pascal’s law

• Pressure
• Force
• Area
• Hydraulic fluid
• Piston
• Mechanical advantage