Calculate Pressure: Potential Energy in Hydraulics

The law of conservation of energy is one of the most fundamental theorems in physics. Simply put, the law of conservation of energy states that energy is not lost, but is always only converted.

A distinction is made between stored “potential energy” and released “kinetic energy”.

A load located at a certain height, for example, has the potential energy of its mass (m), multiplied by the gravitational acceleration (g) and the height (h).

m·g·h

When this mass falls down, it releases the energy ½ m·v² in the form of motion.

Different formulas apply to other physical situations such as heat or light release, expansion of an explosion, or motion in hydraulic systems. However, the basic assumption is always the same: The released energy always corresponds in total to the energy that was previously stored.

What is Hydraulic Pressure Energy?

Hydraulic pressure energy is the potential, i.e., stored energy that acts in a hydraulic system. Since liquids are not compressible, it is not possible to store the energy in the system itself. The pressure in hydraulic systems is therefore always supplied from outside. Typically, this is the kinetic energy of the hydraulic pump. For emergency and backup modules, other pressure accumulators are also available. These operate with spiral springs or with compressed gases.

Hydraulic Pressure as Potential Energy

Pressure is fundamentally a force acting on a surface. The formula is accordingly
Pressure (p) equals force (F) divided by area (A)

p = F/A

It follows that: The smaller the area, the greater the pressure. To design a hydraulic system, two key parameters are therefore important:

• How high does the pressure rise in the system?
• For which pressures are the components of the system designed?

The pressure in a hydraulic system is determined by its requirements. Hydraulics are typically used where high forces are required. The pressure should therefore only be converted into kinetic energy at the points where these high forces are needed.

A simple example is stepping on the brake pedal. The weak muscle force of the driver is intended to reliably press the brake pads located on the wheel brake cylinders against the brake disc, even at high speeds.

Calculating Hydraulic Energy Using Bernoulli’s Equation

To calculate hydraulic energy, Bernoulli’s equation is required. In summary, this formula states that the sum of potential energy, kinetic energy, and the prevailing pressure in a closed hydraulic system always remains constant.

However, this is not entirely accurate, as the heat generated as energy loss is not taken into account here. Nevertheless, this formula is sufficient for the basic design of a hydraulic system.