Hydraulic Machines

Let us learn about Hydraulic Machines,
Let us now consider what happens when we change the pressure on a fluid contained in a
vessel. Consider a horizontal cylinder with a piston and three vertical tubes at different
points. The pressure in the horizontal cylinder is indicated by the height of liquid column in
the vertical tubes.It is necessarily the same in all. If we push the piston, the fluid level rises in
all the tubes, again reaching the same level in each one of them.
This indicates that when the pressure on the cylinder was increased, it was distributed
uniformly throughout. We can say whenever 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 the 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 the Pascal’s
law. In these devices fluids are used for transmitting pressure. In a hydraulic lift as
shown in Fig. two pistons are separated by the space filled with a liquid.
Schematic diagram illustrating the principle behind the hydraulic lift, a device used to lift heavy loads.

A piston of smallcross section A1 is used to exert a force F1 directly on the liquid. The pressure P = F1/A1 is
transmitted throughout the liquid to the larger cylinder attached with 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) F2 = PA2 = F1A2 / A1 . 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.
Hope the explanation helped you, now let us learn about Transmission of Pressure in Liquids.