Hydraulic Machines

The external pressure is applied on any part of a fluid contained in a vessel, it is transmitted undiminished and equally in all directions. This is Pascal’s law for transmission of fluid pressure and has many applications in daily life.

A number of devices such as hydraulic lift and hydraulic brakes are based on Pascal’s law. In these devices, fluids are used for transmitting pressure.

Hydraulic lift:

An important application of Pascal’s law is the hydraulic lift used to lift heavy objects. A schematic diagram of a hydraulic lift is shown in the Fig. It consists of a liquid container which has pistons fitted into the small and large opening cylinders. If a1 and a2 are the areas of the pistons A and B respectively, F is the force applied on A and W is the load on B, then

This is the load that can be lifted by applying a force F on A. In the above equation 2 a1/a2  is called mechanical advantage of the hydraulic lift. One can see such a lift in many automobile service stations

Hydraulic brake:

When brakes are applied suddenly in a moving vehicle, there is every chance of the vehicle to skid because the wheels are not retarded uniformly. In order to avoid this danger of skidding when the brakes are applied, the brake mechanism must be such that each wheel is equally and simultaneously retarded. A hydraulic brake serves this purpose. It works on the principle of Pascal’s law.


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