Another important feature of hydraulic oil is its lubricity. The external friction is a resistance that must be overcome by the hydraulic oil.
The speed with which a liquid flow through a hydraulic system is in turn dependent on the viscosity and lubricity.
The next point to consider is the compressibility of the fluids used. While pressurized air can significantly reduce its volume, oil and water remain under pressure almost without significant volume loss.
With the speed and the compressibility of liquids further influencing factors are added.
The flow of hydraulic oil has a decisive influence on e.g. the energy loss of a hydraulic system.
We distinguish between two types of flow.
• Laminar flow
• Turbulent flow
The Reynolds number Re helps in the rough calculation of flow types.
Turbulent flow causes pressure differences between a liquid and two points in the hydraulic system.
It makes no difference whether the points are located between the inlet and the outlet of a valve or at two distant points in the piping system.
This pressure difference provides for a pressure drop by e.g. Cross-sectional constriction, change in the flow direction, actually by anything that can affect the flow rate.
These influences ensure that a hydraulic system produces the so-called pressure surges.
The shocks are vibrations in the hydraulic system that are triggered by the fluid because the fluid is trying to flow back or change direction.
The liquid trapped between two points is exposed to shock waves at very high speeds.
These shock waves generate a pressure increase which is many times higher than the operating pressure.
These pressure peaks repeatedly lead to damage to hydraulic components, pipes and hoses, the propagation speed of the pressure in liquids corresponds to around three times the speed of sound. The kinetic energy of a pressure fluid must not be neglected in the calculations.
If the liquid returns to the dormant state no more pressure peaks are noticeable.
One way to prevent pressure peaks is to install pressure accumulators in the system. Pressure drops, pressure surges, turbulence and pressure spikes cause energy loss in hydraulic systems.
The energy is converted into heat, which causes an increase in the temperature of the hydraulic fluid and the assemblies.
My wish for the future of hydraulics:
A lubricant that completely prevents mechanical wear. A lubricant that eliminates minor traces of wear. A kind of „nanomechanical oil“ which repairs surfaces on their own and permanently protects them against wear. A lubrication system that uses Cobots autonomously to handle all lubrication tasks of machines and plants.
Nanotechnology, small mini inspectors, they are present in the hydraulic oil and their control everything – pollution, cavitation, flow behavior, wear detection. The Mini inspectors are in all media and ensure a smooth flow. Thanks to various nanotechnologies, the Minicheckers can carry out preventive maintenance and stabilize the times of use an hydraulic system much longer.