Hydraulic power is used in many industries and you can even find hydraulic systems in your car, as they power your brakes and your steering, but how exactly do hydraulics work? Think of a water pistol, which fires out a powerful jet of water due to compression of some kind and this is the same principal that makes a hydraulic system able to move something. Liquid cannot be compressed and when pressure is applied, it pushes the liquid through any aperture, so when you use a powerful pump that forces hydraulic liquid, it will result in a movement.
Pascal’s principle states that force which is applied to one part can be transferred to another point using liquid, which is normally called hydraulic oil, and because liquids cannot be compressed, the transfer of energy is very efficient. So, if you have a reservoir full of hydraulic oil with two pistons and cylinders, one at each end; when you compress one piston into the cylinder, this will result in the other piston releasing along the cylinder, and this transfer of energy forms the basis for hydraulic machines.
Magnifying the Pressure
By making one piston larger than the other, it is possible to magnify the amount of force that is transferred in the process and it is this process that empower the hydraulic system to move very heavy loads. There are specialist companies that sell hydraulic cylinders in Australia that are used in massive excavators and earth moving machines, and due to the huge pressures involved, sometimes these components fail and need to be replaced.
Master and Slave Cylinders
A classic example of a master and slave cylinders is the car braking system; when you press on the brake pedal, this activates the brake master cylinder that drives the fluid down the pipes, and with 4 slave cylinders (one at each wheel) the force created by the master cylinder enables the 4 slave cylinders to force the brake pads against the wheel disc, thus slowing the vehicle down.
When you use a hydraulic pump to force the fluid, this really amplifies the energy transferred, and when one cylinder pushes out, this forces another cylinder in, which could lift the heavy bucket on an excavator. Typically, a modern bulldozer, for example, has many cylinders, pumps, reservoirs and pipes that force the fluid into various sections, which is controlled by a series of valves. The hydraulic fluid must be contained within the system and there must be no leaks, as this would allow air into the system and would also force hydraulic liquid out when under pressure. If the system is enclosed with high pressure seals, then there are no escape routes for the fluid, other than the ones created by the system of pipes and cylinders, therefore by operating certain levers, you can activate pumps and valves that force the liquid into cylinders and this make the machine move in the required direction.
By carefully calculating the size of the hydraulic cylinders, it is possible to greatly magnify the force, enabling powerful machinery to operate.