How Do Hydraulics Work?

How Do Hydraulics Work?

Many people have heard the term hydraulics in relation to their cars or some other type of vehicle or machinery, but most people have very little idea of how hydraulics actually work.  They may have a vague concept of water being used to do something, but that’s about it.  Hydraulics are actually very interesting in how they use water to do what they do.

What Are Hydraulics?

Hydraulics can be a term used for the study of liquids and how liquids function, but most people think of its use in engineering when they hear the term.  Hydraulic systems work by using pressurized fluid to power an engine.  These hydraulic presses put pressure on a small amount of fluid in order to generate a large amount of power.

Here’s a basic idea of a hydraulic system: water in a contained system has pressure put on it from one side.  That pressure forces it against a piston on the other side of the container.  This transfers the energy into the piston, forcing it upward to lift something.  Because the pressure on the water will not let it flow backwards, the piston can never move in the opposite way unless that pressure is released.  This means that whatever the piston is lifting is secure until the system operator allows it to be released.  For example, if the pistons raise the forklift’s prongs, they would remain raised until the hydraulic pressure was released.

Joseph Bramah, Father of Hydraulics

In the late 1700s, British mechanic and engineer Joseph Bramah began working on practical applications of Pascal’s Law, a principle developed by French mathematician Blaise Pascal.  This law states that if pressure is applied to a fluid that is confined in a small space, that pressure will be transmitted through the fluid in every direction without diminishing.  When it hits the edges of the confined space, the pressure will then act against that space at right angles.  Basically, a force acting on a small area can generate a proportionally bigger force on a bigger area.

Example: a pressure of 100 pounds, that’s applied to a space of 10 square inches will generate a pressure of 10 pounds per square inch.  Since a 10 by 10 square actually has 100 square inches in it, the press can support up to 1,000 pounds total.

This may not make sense to most people, but to Bramah, it had potential as a new type of press.  In 1795, his research paid off, and he patented the first hydraulic press.  The Bramah press, as it’s known today, became widely successful.

Parts of a Hydraulic System

Hydraulic systems are made up of four main components.  These components contain the liquid, apply the pressure, and convert the energy generated into mechanical energy for practical use.

The Reservoir: this is where the liquid is held.  The reservoir also transfers heat into the hydraulic system and helps remove air and different types of moisture from the stored fluid.

The Pump: the pump is responsible for moving mechanical energy into the system.  It does so by moving the fluid in the reservoir.  There are a number of different types of hydraulic pumps available, and each works in a slightly different way.  However, all pumps work on the same basic principle of moving fluids through pressure.  Some of these types of pumps include gear pumps, piston pumps, and vane pumps.

Valves: the valves in the system are used to start and stop the system and direct where the fluid moves.  Valves contain a number of spools or poppets. They may be actuated through electrical, manual, hydraulic, pneumatic, or mechanical methods.

Actuators: these devices take the generated hydraulic energy and change it back to mechanical energy for use.  This may be done in several different ways.  The system may use a hydraulic motor to generate rotary motion, or it could be done using a hydraulic cylinder to create linear motion.  There are also a few different types of actuators that are used for specific functions.

What Fluids are used in Hydraulic Systems?

Some people assume that a hydraulic system uses water, and that may have been true at one point.  However, there are other fluids that work much better because in addition to transmitting energy, they also lubricate the system and self-clean themselves.  Here are a few of the different types of hydraulic fluids used today:

Applications of Hydraulic Systems

We see hydraulics in use every day, although most people don’t realize it.  Here are a few examples of how this system is put into use on a daily basis:

Cars and other vehicles:

The most important use of hydraulics in cars is in hydraulic braking systems.  These systems use brake fluid to transfer pressure onto a braking pad, which then presses onto the axel and stops the vehicle from moving.

Some vehicles also feature hydraulic suspension.  This type of suspension lifts the car up off the group so that the ride is much smoother and more comfortable for the driver.


Hydraulics are used in forklifts to lift the load-bearing prongs up off the ground and hold the load in the air while the forklift moves.  The hydraulic system in a forklift has been described as the heart of the vehicle, and that’s true: the hydraulic lifting system does most of the work, and without it, the vehicle won’t be able to move pallets.

NASA Equipment:

NASA makes use of hydraulics in a couple of different ways.  These systems can be used as auxiliary power units on space shuttles and other vehicles designed to leave earth’s orbit.  Shuttles made use of three different, independent hydraulic systems to serve as backup power generators.  Hydraulics were also used in the landing gear to move the gear up into the shuttle body after takeoff and to extend it when landing.

Construction Equipment:

In construction equipment and other heavy machinery, hydraulics may be used to lift, press, or split systems.  Diggers, log splitters, and cranes all make use of hydraulics to operate.  These vehicles often have large scoops or other parts that take a considerable amount of power to operate and would be more expensive and difficult to power were it not for hydraulics.


Hydraulic equipment is most often used to lift or move heavy loads since it’s fairly low-cost but can generate a lot of power.  Even though the idea behind hydraulics is very simple and several hundred years old, because it works so well, engineers have only been able to improve some of the components of a hydraulic system rather than completely replace it with something new.