In my exploration of hydraulic systems, I’ve often been fascinated by how a presse hydraulique multiplies force to perform heavy-duty tasks efficiently. This mechanical marvel operates on the principle of Pascal’s law, which states that pressure applied to a confined fluid is transmitted undiminished in all directions. Understanding how a hydraulic press multiplies the force not only reveals the brilliance of its design but also highlights its applications in various industries. In this article, I will delve into the mechanics behind the presse hydraulique and explain how it can amplify force to accomplish demanding tasks with ease.

Pascal’s law:

Pressure P is the same everywhere there. Pressure P applied on area A2, that means force F2 = P x A2, is much more than force F1 = P x A1 .

Où:

• P is the pressure in the hydraulic system
• F1 is the input force on the small piston
• A1 is the surface area of the small piston
• F2 is the output force on the large piston
• A2 is the surface area of the large piston

Pascal’s law (also Pascal’s principle or the principle of transmission of fluid-pressure) is a principle in fluid mechanics that states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere.

I think you mean for example to lift a car by hand with a presse hydraulique.

A liquid is not compressible (I don’t talk about hypothetical excessive forces).

When you press with a plunger diameter 10mm. in a closed and filled up wilt a liquid (eg hydtaulic oil) and move the small plunger 100mm. You have a (pipe) connection to a bigger cylinder with plunger diameter 100mm. Then the this bigger plunger will move only 1mm. however the mechanical force will be 100x as strong (friction not taken into account)

The oil pressure (force) is in ratio to the surface of the plunger (10x diameter = 100x surface/force).

If you close the pipe by a one direction shutter valve, you can repeat the pump movement and every stroke the big (100mm) plunger will move 1 mm. with 100 fold force)

Here’s how it works step by step in the context of a hydraulic press

Two Pistons:

A hydraulic press typically consists of two pistons with different sizes, connected by a cylinder filled with fluid—usually oil.

Applying Force on a Small Piston: 

When a force is applied to the smaller piston, it creates pressure in the fluid beneath it. Since the fluid is incompressible, this pressure is transmitted uniformly throughout the fluid.

Pressure Transmission: 

According to Pascal’s law, the pressure (defined as force per unit area,P=F/A)exerted on the small piston must be equal to the pressure exerted on the large piston. Therefore, if the small piston has a force F1 and area A1, and the large piston has a larger area A2, the pressure P in the system can be expressed as: P=F1/A1=F2/A2 

Où:

●F1 is the force applied to the input piston

●A1 is the area of the input piston

●F2 is the force exerted by the output piston

●A2 is the area of the output piston

Force Amplification:

Rearranging the equation:P=F1/A1=F2/A2

for F2 (the force exerted by the large piston)This shows that the force F2 is multiplied by the ratio of the areas of the two pistons. Since A2 is larger than A1, F2 is greater than F1.

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