Hydraulic technology: the basics

Applications of hydraulic technology are all around us—the water coming out of your tap and shower, the food you eat, the car you drive, the ship and plane you travel on, the elevator that takes you to your flat or office floor, the jewellery we wear, the buildings we live and work on, all of these were either created or operate on a daily basis using hydraulic tools and equipment. Quite frankly, the convenient modern lifestyle we lead today wouldn’t be possible without hydraulic powered machines.

Principles and theoretical foundations

Hydraulics is a technology using pressurised liquid for doing work. It is used to great lengths where large forces are required to be used for lifting and moving objects with precise control. Humans have used this to our advantage since antiquity by controlling the flow of water in pipes, rivers and channels and storing them in dams and tanks to supply water for household and agricultural use as well as defence purposes. Hydraulics also applies to gases, usually in instances where variations in density are relatively small.

Blaise Pascal (Image from Wikipedia)

Blaise Pascal (Image from Wikipedia)

The study of hydraulics as a science began with Aristotle and Archimedes in Ancient Greece, to Da Vinci, Mariotte and Boyle in the Middle Ages and Enlightenment, to Blaise Pascal, a scientist-philosopher and Daniel Bernoulli, a physicist who formulated the laws on which modern usage of hydraulic power technology operates.

Pascal’s Law says that when a liquid fills a closed container, when pressure is applied at any point it will be transmitted to all sides of the container. Pascal’s Law explains the behaviour of the static factors concerning non-compressible fluids.

Bernoulli’s Principle says that velocity energy gathered from motion can be partly converted to pressure by enlarging a pipe’s cross section so that the flow of liquid is slowed down but the area against which fluid is pressing increases. This Principle explains the relationship of the static and dynamic factors that relate to non-compressible fluids.

The invention of the pump—which converted mechanical to hydraulic energy and produced a greater variety of fluid velocities and pressures—made it possible for Pascal’s and Bernoulli’s discoveries to be applied extensively in hydraulic systems such as that built in London in the 1880s that delivered pressurised water used to power factory machines, and in 1906 for an oil hydraulic system that was made to raise and control the guns on a US warship.

In the 1920s the precursor to the modern hydraulic system consisting of a pump, controls and motor were developed. This broke the ground for creating hydraulic-powered tools, cars, agricultural machinery, locomotives, ships, aeroplanes and spacecraft.

Components of hydraulic systems

There are five main elements that make up hydraulic-powered systems:

  1. Driver: an electric motor or engine that drives hydraulic machinery
  2. Pump: enables the movement of the fluid
  3. Control valves: they are used to regulate the flow of pressure of a fluid
  4. Motor: a counterpart of the pump, it transforms hydraulic energy into mechanical output
  5. Load: how much load on the motor determines the pressure in a hydraulic system

Source of power

What is the most ideal hydraulic fluid for tools and machines? Water, while readily available and cheap is not ideal because it leaks easily and will cause metal components to rust.

The hydraulic fluid commonly used in machines is a type of oil that has the following desirable properties:

  • Correct fluid viscosity
  • Compressibility
  • Wear resistance
  • Oxidation stability
  • Thermal stability
  • Filterability
  • Rust and corrosion protection
  • Foam resistance
  • Demulsibility
  • Hydrolytic stability
  • Seal compatibility

Some types of fluids used in hydraulic systems include multigrade engine oil, automatic transmission fluid and the more conventional antiwear hydraulic oil.