Pascal’s Principle and the Origin of Hydraulics

Did you know that present-day applications of pressure within hydraulics systems derive from a principle developed nearly 370 years ago?

French scientist Blaise Pascal first presented an idea in 1653 that developed into Pascal’s Law, a principle that allows large forces to be generated with relatively little effort. The law is often explained in different ways, but can be summed up as “when pressure is applied on an incompressible fluid, the intensity of the pressure is same in all directions.”

Pascal’s Law continues to be an important foundational element in determining hydraulic systems’ use of compressible fluids (such as oil or water) to transmit forces from one location to another within that fluid.

Pascal’s findings remain pivotal in understanding the transmission of fluid-pressure in all hydraulic systems.

What is Pascal’s Law?

Pascal (1623–1662) was a French mathematician, physicist and philosopher known for developing the modern theory of probability. He also formulated the concept of pressure and showed that the pressure in a fluid – specifically, an incompressible fluid – is transmitted through the fluid in all directions.

Pascal's Law (also known as Pascal's Principle or the principle of transmission of fluid-pressure) is a principle in fluid mechanics that a pressure change in one part of a closed container is transmitted without loss to every portion of the fluid and to the walls of the container.

Therefore, pressure is equal to the force divided by the area on which it acts (P = F/A).

Why Does it Matter?

Hydraulic force is applied for numerous mechanical systems. Understanding many fundamentals, such as Pascal’s Law, can help you as an end-user with the design, troubleshooting, and maintenance of fluid power systems.

A typical hydraulic system with two fluid-filled cylinders, for example, may be capped with pistons and connected by a tube called a hydraulic line. A change in pressure will be transmitted undiminished to all parts of the enclosed fluid, according to Pascal’s Principle.

In a hydraulic pump, which we specialize in here at HPS, mechanical energy from a hydraulic motor is converted into hydraulic power – specifically, flow. This flow creates the necessary pressure to deliver fluid to other parts of the hydraulic system – cylinders, actuators, etc.

This all begins with a vacuum that is created at the pump’s inlet by the mechanical energy of the pump. This vacuum used atmospheric pressure to force the fluid from the reservoir into the inlet line which leads to the pump. The fluid then moves into the hydraulic system.

Pumps themselves do not generate pressure, rather, the flow of liquid from the pump develops pressure and force after exiting the pump – demonstrating Pascal’s principle on fluid that is forced to the elements of the system.

In other applications, such as hydraulic brakes, the pressure exerted on a piston exerts an equal increase in pressure on other pistons in the system, exemplified by the hydraulic press

Pascal & the History of Hydraulics

More than three centuries after Pascal first questioned whether we could channel the forces of liquid, the potential of confined fluids is reaching new limits.

But others contributed to this advancement.

The origins of hydraulics may have first been put into practice in 1738, when Swiss mathematician Daniel Bernoulli is credited for first using pressurized water in mills and pumps.

In 1975, an Englishman called Joseph Bramah patented the first hydraulic press during an industrial revolution, which allowed cranes to lift, as well as machines to begin to cut and stamp.

As time went on, innovations in technology and new materials created greater forces and generated more power, as well as faster and more impressive production. Oil eventually provided even more control of pressurized movement.

Today, hydraulics can give more than 10 times the power of an electric motor and is more effective at lifting heavy objects and forcing things to move.

Pascal’s observations have provided the foundation for these advancements in hydraulics, one of the most important developments in modern mechanical technology.