An Introduction to Hydraulics
Hydraulic systems are found in a huge variety of applications and environments from small assembly machinery or security gates through to piling rigs, theme park rides, supersonic aircraft and the bascules on London’s Tower Bridge.
When it was built, Tower Bridge was the largest and most sophisticated bascule bridge ever completed (“bascule” comes from the French for “see-saw”). These bascules were operated by hydraulics, using steam to power the enormous pumping engines. The energy created was stored in six massive accumulators, as soon as power was required to lift the Bridge, it was always readily available. The accumulators fed the driving engines, which drove the bascules up and down. Despite the complexity of the system, the bascules only took about a minute to raise to their maximum angle of 86 degrees.
Today, the bascules are still operated by hydraulic power, but since 1976 they have been driven by oil and electricity rather than steam.
How hydraulics work…
The use of hydraulics enables the operator to achieve significant work (lifting heavy loads, turning a shaft, drilling precision holes, etc.) with minimum effort through the application of Pascal’s Law, which states that the: “Pressure applied to any part of a confined fluid transmits to every other part with no loss. The pressure acts with equal force on all equal areas of the confining walls and perpendicular to the walls.” Because hydraulic fluid is nearly incompressible, it is able to transmit power instantaneously.
In addition to hydraulic fluid, the main components that make up a hydraulic system (often referred to as a hydraulic power pack or power unit) are the reservoir, pump, valve(s) and the actuators, (the motor, cylinder etc.) Looking at each of these in turn:
Reservoir: The reservoir holds a volume of hydraulic fluid and allows any solid contaminants to settle at the bottom of the reservoir while transferring heat from the system, and helping air and moisture to be released from the fluid.
Pump: The hydraulic pump converts mechanical energy into hydraulic energy by moving, or transmitting, the hydraulic fluid. There are several types of hydraulic pumps including gear, vane and piston (see our Hydraulic Pumps page in our Technical Library for more information). In all cases, the role of the hydraulic pump is to displace fluid volume against a resistant load or pressure.
Valves: Hydraulic valves are used to start, stop and direct the flow of hydraulic fluid in the system.
Actuators: Hydraulic actuators come at the end of the process, where the hydraulic energy is converted back to mechanical energy. This can be done through using a hydraulic cylinder which converts hydraulic energy into linear motion and work, or a hydraulic motor which converts hydraulic energy into rotary motion and work.