Hydraulik Basics

The word hydraulics comes from the Greek and can be derived from the composition of the two words hýdor „the water“ and aulós „the pipe“.

The theory of hydraulics is the theory of the flow behavior of liquids. In engineering and mechanical engineering, hydraulics involves the transmission of forces, energy and signals as well as lubrication.

It’s about pressure and it’s about volume, speed and friction, kinetics and static, and potential and kinetic energy. Hydraulics is versatile and versatile to use.

As one of the „fathers of hydraulics is considered in ancient times Archimedes. The story of examining a golden crown and his brainwave in the bathtub is a story much told to this day. The buoyancy of a body in a liquid should be the birth of the hydraulics, Eureka I called it!

Buoyancy and displacement of objects in the water is also a topic of hydraulics.
In this hydraulic trainer you can get to know the basics of hydraulics and fluid technology.

Where do you first meet a hopefully functioning hydraulic system today?

First there is the heating system of your apartment. It works hydraulically. The heated water is by means of a „circulation pump“ to the „consumers“, the radiators and the shower, promoted and stored in a storage store. Then it goes on the morning walk to the toilet on, hopefully their hydraulic system works, they will notice it when they actuate the „valve“ of the toilet flushing. Thankfully, the water washes the things away. The cistern is automatically filled with water and switches off the „filling valve“ when the set fill level is reached.

Brushing and washing teeth, they turn on the „mixing valve“ of the faucet and it comes water in the desired amount and temperature. All thanks to the functioning hydraulic water system in her house.

For this to work, the hydraulic system must generate a volume flow. This „volume flow“ meets various „resistance“ such as friction in the pipe and pitch of the pipes, etc.

From the resistance, the applied forces, then arises the „pressure“ in hydraulic systems.

Forces transmitted in a hydraulic system are generated by the volume flow generated by the pump. Movement through a volume flow encounters resistance in the hydraulic system (e.g., the force a cylinder needs to do its job). From the factors volumetric flow and resistance or force required results in the resulting pressure.
The required volume flow is generated in the hydraulic usually by a pump which is driven by an electric motor. The hydraulic fluid always stays in circulation with a hydraulic system, in a closed system (water hydraulics can do without it). This means there is a flow and return for the hydraulic fluid. For example, the hydraulic fluid can be conveyed by a pump to a consumer such as a hydraulic cylinder and is returned from there via a return line to the storage tank.

Fundamentals and formulas of hydraulics

Pascal’s Law

The action of a force (F) on a fluid at rest produces in it a pressure (p) which propagates uniformly in all directions and always acts perpendicular to the boundary surfaces of the fluid.

The direction of movement in hydraulics and hydrostatics are two topics. That is, when using multiple cylinders, each individual cylinder will expand according to the force required to lift the load at that location. The cylinders lifting the lightest load first pull out, and the cylinders lifting the heaviest load travel last. Prerequisite is, the cylinders have the same pressure force. This means in practice, pressure always takes the path of least resistance.

For the synchronization of 2 and more cylinders, there are different systems such as e.g. the Graetz rectifier plate. Or cylinders with position measuring system are used.

According to Pascal’s Law, a force acting on a fluid at rest spreads in all directions. Therefore, the shape of a container or tank is not important.

We find the application of hydrostatic pressure in the area of ​​water supply with high tanks or large water reservoirs on roofs of houses. The Tower Bridge in London has been moving hydraulically for decades. Initially, the bridge was powered up by steam engines and water pressure, meanwhile thanks to high-performance hydraulics.

The force that a hydraulic cylinder can produce is equal to the hydraulic pressure multiplied by the „effective piston area“ of the cylinder. F = p × A

The power of the hydraulic pump is composed of the variables P = p x qv. P = power in watts. p = pressure in bar and qv = volumetric flow: second.

The volume flow is composed of the sizes of the cross-sectional area of ​​the tubes (A) and the velocity of the liquids (v). Q = A x v

Printing spreads in all systems in closed systems the same. Liquids are freely malleable and take on the shape of the container.

The size of the effective piston area determined by the pressure of the force of a cylinder.

Properties of liquids that are important in hydraulics.

The viscosity is the fluidity of a liquid. The viscosity describes the effect of the internal friction of a fluid, which means the greater the internal friction, the higher the viscosity.

Viscosity is a measure of the internal friction due to the resistance that occurs with mutual displacement of adjacent layers in a liquid.

High viscosity media overcome resistance in hydraulic systems heavier. The flow resistance is higher than at low viscosity.

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 flows 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. However, in practice there are always air pockets in the fluid and this must be taken into account.

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.