Pressure Energy: Information and Calculation

Pressure energy is the potential energy of a pressurized container. The energy stored in the system exerts pressure on the inner wall of the container. This energy can be referred to as “pressure energy.” A distinction is made between pneumatic and hydraulic pressure energy.

Pneumatic Pressure Energy

The essential difference between pneumatic and hydraulic energy is the ability of gases to be compressed up to the condensation limit. Once a gas has transitioned into a liquid state, it can no longer be compressed further.

For gases, “pressure energy equals pressure times volume” applies.

ED = p·V

Pressure energy is thus the energy that a gas requires for a change in volume or has stored. As soon as the gas can expand, it continues to do so until the pressure energy is consumed or the volume is limited again.

Hydraulic Pressure Energy

In the case of hydraulic pressure energy, no change in volume occurs within the medium. In order to expand, the liquid would first have to be compressed. However, this is not technically possible.

Energy storage for hydraulic pressure energy therefore does not occur within the medium itself, but in the outer wall of the vessel. It is irrelevant whether the pressurized liquid is at rest or flowing through a piping system. As soon as the liquid flows into a pressureless environment, such as an open container, it immediately loses its pressure energy.

The energy is converted into a volume flow that dissipates quickly. The exact calculation of hydraulic pressure energy is performed using “Bernoulli’s equation.”
This is a law of conservation of energy expanded to include volume flow calculation.

Etotal = ED + Epot + Ekin = pV + 1/2mv² + m·g·h

As with all forms of energy, pressure energy always remains constant within a closed hydraulic system.

The following must be noted: Pressure is force per area. Force is mass times acceleration. Energy is force times distance. Instead of the gravitational acceleration in m·g·h, the mechanically generated pressure can therefore also be used as a basis for calculation in vertical hydraulic systems. In the case of downpipes, however, gravitational acceleration should always be taken into account, even if the majority of the pressure is produced by pumps.

Generation of Pressure Energy

Thermal and mechanical processes are possible for the generation of pressure energy. Thermal processes are found, for example, in absorption refrigeration systems. These are hydropneumatically operating cooling systems in which a refrigerant constantly changes between liquid and gaseous states. An additional compressor is not required in absorption cooling systems.

If mechanical pressure is to be used to perform work, various pumps are utilized. In pneumatics, the range extends from simple blowers and compressors to piston compressors. In hydraulics, different types of pumps handle the task of generating pressure energy. Gear or vane pumps are sufficient for simple circulation tasks. For the generation of high operating pressures, radial or axial piston pumps are the best choice.