INTRODUCTION TO HYDRAULIC SYSTEM
1.1. PRINCPLES OF HYDRAULICS
The name ‘Hydraulics’ has been taken from the Greek word ‘HYDOR’ meaning
water and ‘AULOS’ meaning pipe. For the first time ‘Hydraulics’ was put to use by the
person who converted the energy of flowing water into useful mechanical energy, by
means of the water wheel. Later on the idea of Industrial Hydraulics or Oil Hydraulics
emerged. It is the science of transmitting energy through the medium of pressurized
fluid. Advancement of this science started when Pascal discovered a fundamental law
called Pascal’s law which states: “Pressure generated at one point in a confined liquid,
acts actually in all directions and acts perpendicular to the surface of the container”. The
law helped in developing this new field of hydraulics, dealing with power transmission,
control of mechanical motion and characteristics of fluids under pressure. The
developments resulted into the use of network of high-pressure of fluid pipes from the
pressure generating station i.e. pump to the application points through the controlling
system. In this process various auxiliaries like valves, accumulators and seals etc. were
invented. Now-a-days, the principle of oil hydraulics are applied for power transmission
and control and very successfully replaced even mechanical and electrical drives in some
machine-tools and equipment.
The logical and sequential arrangement of various elements to obtain the desired
function through fluid is called hydraulic system. Oil hydraulic systems can be built using
readily available standard elements together with electrical/ pneumatic interface to
perform any complicated sequence of operation. The system is more widely used in
machine tools as principal and feed movement drives providing rotary as well as
translatory motion with stepless regulation of feed and speed rate , speed changing
devices, automatic control of machine cycle, etc. The innovation of electro hydraulic
servo valve and proportional valves, which could conveniently interface with electrical
and electronic measuring and signaling devices, led to the popular use of electro-
hydraulic servo drives in CNC machines. The latest is the application of electro-hydraulic
stepping motors with hydraulic torque amplifiers for feed drives in an open loop
configuration. This extensive use of hydraulic system is due to their capability of
providing infinitely variable speed over a wide range, smooth reversal of moving
machine members, automatic overload protection, easy lubrication, etc. Among their
shortcomings is leakage of hydraulic fluid through seals and gaps, ingress of air into
fluid, effect of temperature and time on fluid properties, etc.
