What are Hydraulic Systems?

The next time you drive a car, get in a lift, or see a crane lifting a huge weight, stop to think about where all the force generated by the machinery comes from. The answer is the use of hydraulic systems, and they are used everywhere. Transportation, construction sites, robotics, the list is long. Any machine that needs to amplify and transmit forces efficiently, is likely to use hydraulics to do so. 

Brief history of hydraulics

Advanced as hydraulic systems are today, the technology is not new. According to the Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures:

“Neolithic hydraulic technology in Egypt developed alongside agriculture, when Egyptians began to alter the river’s regularly flooded banks to grow more crops more easily along the Nile (c. 5700–c. 2800 BCE).”

Nearly two thousand years ago, Heron, a great inventor of Alexandria, described what is considered the first steam engine. Known as the Aeolipile it used pressure created in a central chamber to force steam through the exiting pipes.

It was the French mathematician Blaise Pascal who in 1663 published what has become known as Pascal’s Law, the mathematics that underpins all hydraulic systems. The law states:

“Pressure applied to a confined fluid at any point is transmitted undiminished throughout the fluid in all directions and acts upon every part of the confining vessel at right angles to its interior surfaces and equally upon equal areas.”

This means if you apply a force of 10 kg on an area of 10 square centimetres, the resultant pressure (1 Kg / Cm 2) will be transmitted throughout an enclosed system. This pressure can then be used to support a 100 Kg weight, with an area of 100 square centimetres. Hydraulic systems allow forces to be amplified and moved.

How does a hydraulic system work?

As you may recall from school, matter can be a solid, liquid or gas. Liquids have properties of both flowing easily through pipes and resisting compression. It is this that is exploited in a hydraulic system. A force, from a weight or piston, is used to try and compress the liquid. As the water resists the compression, it is pushed down a narrower pipe, which causes the liquid to travel at a higher speed. This additional speed can be used to power an actuator at the other end, to perform some required task. The system works in reverse too. If a force is applied to the narrow end of a longer pipe, it will generate a force capable of moving something much heavier at the other end.

Components of a hydraulic system

An enclosed hydraulic system is made up of five basic components

1. Hydraulic fluid

This is the medium by which power is transferred. The fluid must flow efficiently and be very resistant to compression. Hydraulic fluids are often based on mineral oil or water. 

2. Reservoir

The hydraulic reservoir holds the fluid required to supply the system, including a reserve to cover any losses from minor leakage and evaporation. The reservoir is designed to provide space for fluid expansion, permit trapped air in the fluid to escape, and to help with cooling.

3. Pump

The hydraulic pump transmits mechanical energy into hydraulic energy. This is done by the movement of the hydraulic fluid. Types of hydraulic pumps include gear, vane, and piston. All hydraulic pumps work on the same principle, which is to displace fluid volume against a resistant load or pressure.

4. Valves

Hydraulic valves are used in a system to start, stop, and direct the flow of the pressurised fluid. Hydraulic valves can be actuated by pneumatic, hydraulic, electrical, manual, or mechanical means.

5. Actuators

Hydraulic actuators are the output from the system, where the inputted hydraulic energy is converted back to mechanical energy. This is done using a hydraulic cylinder or motor, producing linear or rotary motion respectively.

How Autoguide use hydraulics

Advanced hydraulic systems are used extensively throughout Autoguide’s range of machinery. Our crane mounted auger drives, for example use Hydraulic Fold-Up Brackets, to allow the Powerhead to be stowed for transport and to allow the crane to be used for pole work without removing the attachments. Our screw pile torque heads, both hand-held and excavator mounted, use a hydraulic system to generate the rotational forces required to penetrate the soil. The TC600 – Terrain Master uses hydraulics not only to power loader cranes and work platforms, but also to provide stability via optional hydraulic legs.

Hydraulic systems may not be new, but they are a vital part of any modern construction machinery. Efficiently amplifying, controlling and applying forces, exactly where and when they are needed. We wonder if the Egyptians, the great inventor Heron or the mathematician Blaise Pascal, knew quite how important their contributions would be in the twenty-first century?