Navigation:  Library > Iconic Diagrams > Hydraulics >


Previous pageReturn to chapter overviewNext page

The 20-sim Hydraulics library contains components to model the dynamic behavior of hydraulic circuits. The library has been completely revised in 20-sim 4.9. Compared to older versions of 20-sim the following changes are made:


1.Most valves and components now use the nominal flow at a given pressure drop to determine the laminar and turbulent flow characteristics.
2.Fluid Properties are now defined with a separate component.


To get a good impression of the use the components of this library, have a look at the example circuits.


The Hydraulics library is divided in a number of sections:

Components: Connectors and lines
Cylinders: translational actuators
Fluids: fluid properties
Motors: motors
Pumps: flow and pressure sources, pumps
Restrictions: orifices and restrictions
Sensors: flow and pressure sensor
Valves: check valves, pressure reducing valves, 4-3 way valves and more
Volumes: volumes, tanks and accumulators

Some of these sections contain subsection with basic components. These elementary components (without parasitic volumes) should only be used by experienced modelers who want to create their own library components.

Fluid Properties

In previous versions of 20-sim, the hydraulic fluid properties (eg. bulk modulus, viscosity) were stored in every component. In this library the fluid properties are stored in the Fluid Properties component. This means that you only have to define the properties once, and use them in every component automatically.


Every library component has one or more hydraulic connectors, which are called ports in 20-sim. Ports always have two variables: pressure [Pa] and volume flow [m3/s]. The following ports a and b are usually provided:




Pressure in [Pa] with respect to atmospheric pressure (p stands for pressure).


Volume flow [m3/s], positive if oil is entering the component at port a (phi stands for flow).





Pressure in [Pa] with respect to atmospheric pressure (p stands for pressure).


Volume flow [m3/s], negative if oil is entering the component at port b (phi stands for flow).

Hydraulic components can easily be coupled to other library models. The pumps and motors have a rotation port that can be coupled to models of the Rotation library. The cylinder models have a translation port that can be coupled to models of the Translation library. Some models have a variable input that can be coupled to models of the Signal library.


20-sim uses SI-units for the hydraulic components. If you want to use other units select them in the Parameters Editor or the Variables Chooser. The 20-sim hydraulics library uses the common definition of pressure in Pa:


1 Pa = 1 N/m2 = 1e-5 bar


The air pressure at sea level is taken as the zero value:


0 Pa = air pressure


Consequently the pressure for liquid oil that starts to vaporize is negative. In 20-sim the default value of the vapour pressure is:


p_vapour = -0.999e5 Pa


The vapour pressure is the minimum pressure. Some models have a safeguard on the pressure to prevent it to become smaller. You can change the value of the vapour pressure but take care that always a value is chosen that is smaller than zero. Otherwise some of the models will not work correctly.

Parasitic Volumes

Most components have parasitic volumes to ensure a seamless connection with other components. Therefore almost all components can be connected arbitrarily.


All models have been tested with standard configurations. This will however not ensure that valid results will be found at all times. For example temperature effects are not included and certain parameter values will lead to unstable simulations. Therefore any application of the library without validation of the user is at his own risk!


The 20-sim hydraulic library has been based on the following literature:


P. Dransfield, Hydraulic Control Systems - Design and Analysisi of Their Dynamics, Springer 1981,ISBN 3-540-10890-4.

P. Beater, Entwurf Hydraulischer Maschinen, Modelbildung, Stabilitätsanalyse und Simulation hydrostatischer Antriebe und Steurungen, Springer 1999, ISBN 3-540-65444-5.


The models have been designed as close as possible to the Modelica hydraulic library (www.modelica.org). To compare both libraries the example model Closed Circuit Drive Train.emx has been added.