Water in oil-based hydraulic systems is a source for many machinery failures. It accounts for up to 20% of the
life expectancy failures and even before that, it impacts the expected performance negatively /1/. Water can enter
a hydraulic system in various ways. In this article, the entry through the dynamic seal of the rod is investigated.
After a brief description of the damage mechanisms of water in a hydraulic system, the theory of the entrainment
is explained. The test bench is then described to study the effect. Finally, entrainment results for two test fluids
(oil and water) are presented and compared to the theory.

The DOT concept for offshore wind energy is a seawater hydraulic network where turbines are directly
coupled to a centralized hydro-power platform. The essential missing component is a low-speed hydraulic
pump that uses seawater as its hydraulic medium. This low speed hydraulic pump is currently being
designed and tested by DOT, where novel machine components have been developed. This paper describes
the development of an interface between an oval running track which is used as eccentricity to actuate a
hydraulic piston. Several approaches have been performed as well as prototyping and validation steps.
These steps as well as the design approach are presented in this work.

Free gas in a hydraulic system is usually accompanied by negative aspects. Currently available models usually underestimate degassing at liquid-gas interfaces that are exposed to fluid flows, which is the most relevant degassing mechanism in hydraulic systems. Therefore, a new approach for physical modelling of bubble formation at liquid-gas interfaces is presented. Based on recent findings on diffusion-driven nucleation a simple model to calculate the mass fraction of gas being set free in a hydraulic fluid is derived. This approach is experimentally validated and could be implemented in available calculation tools.

Wear in swashplate type axial piston pumps mainly occurs in three tribological contact pairs. These are
swashplate-slipper, piston-cylinder and cylinderblock-valveplate. This article focuses on a simulation model,
based on the approach of Archard and Fleischer, to predict the wear in the piston-cylinder contact. Besides
general geometric data, the exact piston and cylinder contours and the wear-induced material removal over time
are taken into account. A special focus in the simulation is on the investigation of the dependency of the
viscosity of the hydraulic fluid on the wear. First results from test runs demonstrate a good correspondence
between the simulation and measured wear on a test bench.

An integrated retainer which wraps the slippers and rotates with them is assembled in an Electro-hydrostatic actuator (EHA) pump, to eliminate the high linear velocity at slipper bottoms and to diminish the PV (pressure×velocity) value of the contact area. The impacts of laser surface texturing on the performances of the high-speed rotating retainer are investigated by conducting the CFD simulation of the flow inside several micro-dimples and the experiments on an EHA pump prototype. Wear marks are observed and the dimples with an area ratio of 16.4% are found to improve the volumetric and mechanical efficiencies of the prototype by up to 7.4% at the speeds of 6000~10000 rpm.