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FIGURE 20.89 Hydraulic servocylinder (Hanchen).

The first group obviously includes hydraulic oils, that is, fluid with high viscosity, now traditionally
used in servosystems in which a high controlled pressure is requested, but also combustible fluids, such
as automotive or aeronautical petrols (JPA, JPB,…), used in all the applications found in the fuel circuits
of combustion engines. Other servosystems include those which use both industrial and seawater as the
working fluid. The latter solution has unquestionable advantages in all naval and off-shore applications.
Pneumatic servosystems include all the industrial applications for automation of production and
process automation, and also the vehicular applications on means of air, sea, road, and rail transport.
The compressed air in these applications is generated by compressors using air drawn in from the
environment. Further applications include those in which the working fluid is not compressed air but a
particular gas. In this regard, there are servosystems with refrigerant fluids in the gaseous stage, in both
vehicular and industrial cryogenic systems, with fuel gases (LPG, methane, propane) in domestic appli-
cations, and with nitrogen in high-pressure applications.
It can be seen from this preliminary analysis that fluid servosystems are present both in the realization
of a product, being integral parts of the automated production process, along with the electric servo-
mechanisms, and as controlled actuation devices integrated in the product itself; in this regard we can
mention generic servoactuators installed on aeroplanes and increasingly in road vehicles today.

Hydraulic Actuation Systems

The components of a hydraulic actuation system are:
• the pump, that is, the hydraulic power generation system;
• the actuator, that is, the element which converts hydraulic power into mechanical power;
• the valve, that is, the hydraulic power regulator;
• the pipes for connecting the various components of the actuation system;
• the filters, accumulators, and reservoirs;
• the fluid, which transfers the power between the various circuit elements;
• the sensors and transducers;
• the system display, measurement, and control devices.

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