Hydraulic Press is one of the applications of Pascal’s Law.
Joseph Bramah designed the hydraulic press in1795.
In a hydraulic press, a small force applied on a column of liquid is converted into a much greater force available to another column of liquid connected to the first.
Let us see how this happens
In a hydraulic press, there are two cylindrical tubes A and B of unequal area of cross sections fitted with valves V1 and V2. These cylindrical tubes are connected at the bottom by means of a horizontal tube.
These cylinders contain water tight piston P1 and P2 which can slide up and down within the cylinder.
Observe that area of cross section of B is greater than that of A.
The tubes are filled with water in such a way that the level of water in both the tubes are equal.
The smaller cylinder is called the pump plunger and the larger cylinder is called the press plunger.
To press down or raise the pump plunger, there is a lever arrangement with a handle.
Now when a force is applied to the piston P1, it exerts a pressure on the liquid contained in the smaller cylinder or pump plunger.
According to Pascal’s Law, this pressure is transmitted to the piston of the press plunger and due to which the piston P2 is pushed outwards.
Since the area of cross section of the pump plunger is less than that of the press plunger, the applied force is multiplied.
Thus by applying a small force on the smaller cylinder, we can lift or compress a large weight kept on the piston of the press plunger.
Hydraulic press is used for compressing bales of cotton, extracting juice from sugarcane and for extracting oil from cotton seeds.
Here you can see how a hydraulic press is used for compressing bales of cotton.
When the pump plunger S1 is raised with the help of the lever, the pressure inside cylinder A decreases and as a result, the valve V1 opens upwards and water from the tank is pushed into cylinder A.
When the pump plunger S1 is pushed downwards by lowering the lever handle, the valve V1 closes due to increase in pressure in cylinder A. As a result, water from cylinder A flows to the connecting tube C. The pressure in C is greater than that in cylinder B and therefore, the valve V2 opens. The water from cylinder A is forced into cylinder B due to which the press plunger S2 is raised against the fixed roof and the bales of cotton placed on the press plunger S2 gets compressed.
Near the bottom of cylinder B, there is a tube fitted with a release valve.
After the cotton is pressed, this valve is opened so that the piston of the press plunger S2 gets lowered and the water from cylinder B is released into the tank.