Edge welded metal bellows accumulators are the cutting edge of hydro-pneumatic accumulators. Compared with
other designs such as diaphragm-, bladder- or piston accumulators the gas chamber is usually hermetically sealed
and the metallic barrier between gas and fluid side shows no permeation. This design is maintenance free and
keeps its performance for the whole service live. They have extraordinary media compatibility and an extremely
wide operational temperature range.
HYDACs newest design is mounted on a jet engine. It withstands very high external loads such as vibrations,
shocks and fire. One special feature is an indicator which allows checking the integrity of the metal bellows
without having a sealed component.

This paper contributes to the topic of modelling noise generation and propagation in hydraulic pumps,
particularly focusing on the external gear pumps. By using proper methodologies for the fluid, structure, and air
domains, the model proposed in this study can predict the resultant noise emissions coming from the interactions
between these three domains. Two cases of numerical simulations were performed, considering a different
complexity for reproducing the pump mounting conditions. For validation purposes, noise measurements were
taken in a semi-anechoic chamber on a commercial unit. The effects of the mounting situation on the overall
emitted noise as well as the level of the agreements between simulation and experiments are discussed.

Driving signals of electromechanical control valves require a well dosed dynamic excitation to reduce hysteresis
and to optimise dynamics. Nevertheless, a knowledge based signal definition and parameterisation is rarely
possible. The paper attempts to close this knowledge gap by analysing the valve’s dynamics with commonly
used signals and control schemes. Hence, parameter estimation rules for adapting given parameters for one
signal form to another are deduced. Finally, experimental validation of the findings is carried out by comparison
of the dynamics of a customary valve driven by the different control signals. The paper concludes with
recommendations for dither signal parameterisation.

Pressure pulsations are caused by the flow ripples from a positive displacement hydraulic pump. They are
transmitted throughout fluid power equipment and cause unwanted excitations of the mechanical parts. In many
practical applications, a Helmholtz type hydraulic silencer may be used to attenuate such pulsations. It is the
preferred solution on account of its simple structure and high attenuation performance. However the distinctive
drawback of this silencer is that it is effective only within a narrow range of the attenuating frequency. Therefore,
the silencer is only suitable for use in hydraulic systems, running at constant pump rotational speeds. The
purpose of this research is to develop a novel silencer for hydraulic systems that have a fixed displacement pump
driven at variable rotational speeds. First, a mechanism for adjusting the resonant frequency has been proposed.
This works by changing the volume of the silencer. Secondly, a prototype of the novel silencer was designed
using a new distributed parameter system model, in which the vessel volume was modelled as an annular fluid
line. Finally, the attenuation characteristics of the prototype silencer were verified by measuring the transmission
loss under various conditions, and comparing them with the calculated results.