These are machinery and tools that use fluid power for its functioning. In these machines, a large amount of power is transferred through small tubes and hoses. Here, fluid is transmitted throughout the machine to motors and hydraulic cylinders where it gets pressurized and further transferred to the end effectors through control valves and tubes.

Pascal’s Law

According to Pascal’s law for the transmission of fluids, whenever external pressure is applied on any part of a fluid contained in a vessel, it is transmitted undiminished and equally in all directions.

Applications

• Hydraulic lifts

The hydraulic lift is an elevator which is operated by fluid pressure generated by a suitable fluid. It is used to raise automobiles in service stations and garages. In a hydraulic lift, two pistons are separated by the space filled with a liquid. A piston of small cross section A1 is used to exert a force F1 directly on the liquid. The pressure P =F/A is transmitted throughout the liquid to the larger cylinder attached to a larger piston of area A2, which results in an upward force of P × A2.

Therefore, the piston is capable of supporting a large force (large weight of, say a car, or a truck, placed on the platform).

By changing the force at A1, the platform can be moved up or down. Thus, the applied force has been increased by a factor of A2/A1  and this factor is the mechanical advantage of the device.

• Hydraulic Brakes

Hydraulic brake is an arrangement of the braking mechanism in which suitable brake fluid is used to transfer pressure from the control mechanism to the brake mechanism. Hydraulic brakes in automobiles also work on the same principle. When we apply a little force on the pedal with our foot, the master piston moves inside the master cylinder, and the pressure caused is transmitted through the brake oil to act on a piston of the larger area.

A large force acts on the piston and is pushed down expanding the brake shoes against brake lining. In this way, a small force on the pedal produces a large retarding force on the wheels. An important advantage of the system is that the pressure set up by pressing a pedal is transmitted equally to all cylinders attached to the four wheels so that the braking effort is equal on all the wheels.