The most common type of braking system used in automobiles and other machines today

is hydraulic brakes. Prior to the advent of hydraulic brake systems, cars used mechanical brakes.

Hydraulic brakes apply more pressure to break pads than mechanical brakes because they use

compressed fluids. This helps the vehicle to stop with more force, without requiring the driver to

apply more force (Haverdink). I decided to research this topic because I have hydraulic brakes on

my mountain bike which help me to brake safely when traveling down slopes. This log will

specifically focus on hydraulic presses, how they are implemented into the hydraulic braking

system on a car, and the advantages of hydraulic brakes compared to mechanical brakes.

To begin, a hydraulic braking system is similar to a hydraulic press. A simple hydraulic

press consists of a cylinder that contains two pistons, one smaller than the other (Chalupnik). The

cylinder is filled with a liquid called brake fluid that has a low freezing point, a high boiling, and

the ability to absorb water (Kelsey). A force applied to the smaller piston is transferred through

this brake fluid to the larger piston (Chalupnik). The effect this causes can be explained by

Pascal's law which states that when there is an increase in pressure at any point in a confined

fluid, there is an equal increase in pressure at every other point in the container (Hodanbosi)

Therefore, if pressure is applied to the smaller piston, the pressure is increased throughout the

cylinder and affects the pressure of liquid on the large piston creating more force in the

movement of the large piston (refer to figure 1 in the Appendix). The reason the force generated

by the large piston is higher, even though the pressure is the same, is because the pressure is

being applied to a larger area in the large piston. The extra force this system creates is why it is

present in the brakes on cars.

The hydraulic system used for brakes on a vehicle has the same properties as a hydraulic

press in that it increases force (Chalupnik). However, instead of having a single cylinder with

two pistons, hydraulic brakes have a five cylinder system with each cylinder containing one

piston. This is because there is one master cylinder located near the brake pedal and a cylinder

for each wheel of the car. In this system, the master cylinder contains a small piston and the

wheel cylinders contain larger pistons. Brake lines connect the master cylinder to each wheel

cylinder allowing brake fluid to flow evenly from the master cylinder into each wheel cylinder.

The master cylinder is mechanically connected to the brake pedal so that when the pedal is

pressed, the piston slides forward through the chamber exerting pressure on the brake fluid. The

fluid transmits this pressure through the brake lines, forcing the pistons in the wheel cylinders to

slide forward. As the wheel cylinders move forward, they apply break pressure to pads or shoes

which either close around a disk, or push against a drum in the wheel depending on which kind

of brakes are used in the wheels of the vehicle (Haverdink).

Another type of brakes are mechanical brakes that uses levers or cables which connect

the brake pedal directly to the braking pads. For the car to stop faster, the driver has to apply

more force to the brake pedal. On hydraulic brakes, the extra force is applied through the brake

fluid (Haverdink). This makes hydraulic brakes safer because the driver does not need to apply a

lot more extra force in order to stop more quickly. As mentioned earlier, when there is an

increase in pressure at any given point in a confined fluid, there is an equal increase in pressure

at every point in the container(Hodanbosi). In the case of hydraulic brakes, this means that the

force applied to a brake pedal increases through the other pistons present in a hydraulic braking

system and therefore applies a greater amount of force to the brake pads than the original force

of the drivers foot against the brake pedal. Therefore, vehicles are able to slow down faster

because of the increased pressure on the brake pads, and drivers do not need to apply as much

force on the brake pedal as they would have to with mechanical brakes. This is why hydraulic

brakes are both safer and more effective than mechanical brakes.

Living in mountainous Colorado, I really enjoy mountain biking with my father. Without

my bike’s various hydraulic systems I would not be able to do this as well. I decided to research

hydraulic brakes because I use them on my mountain bike and wanted to learn more about the

scientific processes they perform that allow me to stop easier on my bike. While I did focus on

researching the hydraulic brakes present in automobiles for my topic section, mountain bikes

also have similar hydraulic systems that carry the same properties as the hydraulic press. The

brakes on mountain bikes use a hydraulic system because the rider needs to stop suddenly when

facing difficult obstacles. The extra force that hydraulic brakes provide in stopping the bike is

also needed to counteract the force of gravity that pulls the bike down the hill. The mountain

bike has other hydraulic systems such as front and rear suspension shocks which are similar to a

hydraulic press and help to make the bike ride smoother over rocks and ledges in the trail. In

addition, many newer bikes have an adjustable seat post that use a hydraulic system that raises

and lowers the seat while riding. This seat post system allows the rider to get his weight lower

on the bike for steep descents, but also allows full leg extension during climbs and level riding.

The hydraulics present on mountain bikes help me and bikers all over the world to traverse

mountains and enjoy the outdoors.

Another part of hydraulics that interests me is their many uses in society because of the

mechanical advantage they provide. Hydraulic presses and pumps are examples of mechanical

advantage which is the ratio of the force that performs the work of a machine to the force that is

applied to a machine ("Mechanical Advantage"). In this case, the force applied to a hydraulic

pump (eg. the brake pedal) is far less than the force it performs in doing it’s task (e.g. applying

the brake pads to the disk) and therefore hydraulics give us mechanical advantage. This very

principle allows us to construct tall buildings, build bridges, and dig huge tunnels with hydraulic

systems. The construction of taller buildings allows for more condensed populations which

means that a city can support more people and also more businesses. The digging of tunnels has

helped with the transportation of goods through mountains, and has also helped with mining for

resources. Lastly, the construction of bridges has helped to make travel over bodies of water

easier. These are all example of how mechanical advantage from hydraulics and other systems of

mechanical advantage help our society.

Another interesting part about hydraulics is its use in civil engineering. The machines

built with hydraulics explain the mechanical side of hydraulic engineering, but civil engineers

use hydraulics to study the flow of water in rivers and pipes. Understanding the forces of a

hydraulic system helps people in this field to design embankments and levees that provide flood

control along rivers. It also helps in the creation of irrigation systems and water supply systems

for cities (Chalupnik). This would have been very important in Colorado last year when many

rivers flooded because of heavy rains. More and better levees along the rivers and creeks may

have reduced the flooding, damage to many homes, and loss of life.

For my further development, I decided to address problems associated with bunk beds

using a hydraulic system. While bunk beds are convenient for maximizing space in a bedroom,

they are very dangerous. Between 1990 and 2005, almost 573,000 kids from infants to age 21

suffered injuries significant enough to warrant a visit to the emergency room (Aleccia). These

injuries were most likely caused by the height of bunk beds and climbing of a ladder in order to

reach the top bed. Climbing down from the ladder can also be quite dangerous to young children.

With the safety of children in mind, I came up with an idea to solve this problem.

My idea is that there could be a hydraulic piston system within the legs of the bunk bed.

The pistons in the legs would change the height of the top bed while the bottom bed would

remain a normal height from the floor. The force to raise the pistons could be applied similarly to

that of a car jack. A lever could be connected to the bottom of a cylinder positioned next to one

of the bed legs. For now this will be called the master cylinder. The master cylinder would

contain a piston smaller than the pistons in the cylinders in each bed leg and would be filled with

hydraulic fluid. It would be connected to the cylinders present in each of the bed legs using

piping similar to brake lines. When it's time to go to sleep, a kid could easily climb into bed, and

then his parents could simply step on this pump lever to pump fluid into the bed legs. Stepping

on the lever would cause the small piston in the master cylinder to pump the hydraulic fluid from

the master cylinder evenly into each bed leg cylinder through the lines connecting them. The

pressure applied to this liquid by the small piston would in turn raise the height of the larger

pistons in each of the bed legs. This would cause the top bunk of the bed to raise gradually until

it was an acceptable height above the bottom bed. Once the height is met, the lever would be

pressed down once more and secured with a metal rod connected to the cylinder. Once the lever

is secured, a valve would close off the lines connecting the bed leg cylinders and the master

cylinder. This would keep the hydraulic fluid from seeping back into the master cylinder under

the weight of the bed and therefore keep the bed from falling back down. At this point, with the

top bed secured, another kid could climb into the bottom bunk. Then in the morning, the kid

could climb out of the bottom bunk and the system could be lowered gradually by releasing the

lever. Under the weight of the bed and the kid laying on it, the hydraulic fluid in the bed leg

cylinders should return through the piping to the master cylinder and therefore the bed should

gradually lower until it returns to its down position. A more advanced system could use an

electric hydraulic pump with activation switches located on the headboard of the top bed. This

system would allow a kid to raise and lower the bed themselves while laying on the bed.

This idea helps to keep kids safe around bunk beds as they do not have to climb a ladder

to get in and out of bed. Another advantage is that while the bed is in the down position, it will

be easier to change the sheets. While these advantages do help families who want a bunk bed

because it saves space, the cost of this bed would be much more expensive than a normal bunk

bed. Another problem is the safety pieces implemented to keep the top bed from falling back

down once it has been pumped up to its top height. Developing this would require further

research on the durability of pistons over extended periods of time, as the pistons in each of the

cylinders would need to remain working for multiple years. Developing this would require

further research on hydraulic lock systems similar to the ones used on an elevator to prevent the

bed from falling in the case of a hydraulic failure. Once these problems are addressed, I think

this idea could help to decrease the number of injuries caused by bunk beds.

In my topic section I discussed the use of pistons and hydraulic fluid to apply a greater

amount of force to brakes. To further my understanding of how hydraulic systems can be used to

apply force to lifting objects instead of applying force to brakes, I decided to build a simple

hydraulic crane model. This model was constructed out of wood cubes, crafting sticks, two

plastic syringes, and vinyl piping (refer to figure 2 in the Appendix). I started by creating a base

for the crane, so that it would stand upright, and then created a tower that provided a starting

height for the crane's arm. The arm was then attached using cable ties between two blocks with

holes through them. These tied blocks at the base of the arm acted as the fulcrum for the crane.

Next I attached another block with a hole through it to the top of one of the syringes. The syringe

was connected to another syringe with vinyl piping and both were filled half way with vegetable

oil. The syringe with the block attached to it was then taped to the crane's tower and the block

was cable tied to the arm of the crane. This completed the construction of the model.

With the model completed, I started to test its movement. The two syringe plungers acted

as pistons. I held one of the syringes and applied force to it by pushing down the plunger. This

force compressed the oil in the syringe and caused it to flow through the vinyl piping into the

syringe attached to the crane's tower. The increase in fluid in the syringe connected to the crane

caused its plunger to lift up and therefore lift the arm of the crane (refer to video 1, linked in the

appendix). This was a hydraulic system because the force was applied to liquid which then

applied the force to the crane's arm. However, this system did not offer any mechanical

advantage because the two pistons were the same size. If the piston I was holding was smaller

and the piston attached to the crane was larger, than a greater amount of force would be applied

to the crane's arm with less force applied to the syringe I was holding. To test this further, I could

remake the model with different sized syringes, and attach a string to the arm to lift different

weights.

I did notice a problem with my model after performing a few tests. When I pulled out the

plunger of the syringe I was holding, the other syringe still lowered, but it didn't lower as

smoothly as it had when it lifted. I found that the source of this error was that there was air inside

the syringes. The air would compress more than the liquid would and so it would cause the

plunger to fall in sudden stops instead of lowering smoothly (refer to video 1). From this

problem, I learned that if air is present in a hydraulic system, it will cause the system to fail or

prevent it from completing its objective. Therefore, if air is somehow let into a hydraulic braking

system, it may cause the brakes to stop working. This means that there must be certain seals in

place to keep the system contained and keep contaminants out.

Upon doing my application, I faced a problem. As mentioned above, I noticed that there

was air present in the hydraulic system I had created and this caused the system to not work

correctly. This led me to thinking that hydraulics may not be as safe as I had thought. If air

happens to contaminate the system, then it will fail. This means that there must be seals in place

to prevent this from happening. If these seals fail and air is let into the system, is there a way to

remove air from the system or does it have to be rebuilt? During my research, I came across

articles explaining what happens when hydraulics fail in planes, but many of them mentioned the

system leaking, as if hydraulic fluid from the cylinders had seeped out of the cylinders. Though,

this is not what I am trying to address. Since my system failed because of air, I wanted to look

into other times when systems have failed because of air contamination, but I could find none.

Finding a solution to this could help me to fix my hydraulic system without having to reset the

syringes with new oil. While I couldn't find articles explaining this kind of contamination, I

figure it could still happen. There must be a solution to it because if a person is to build a

hydraulic system for a car, then they don't want to have to fix it when air contaminates it. There

could be some sort of scrubber that can be used to release air without releasing the fluid from the

system. If there isn't a solution to this problem, than there must be a lot of different materials in

place in order to keep air from permeating the cylinders and disabling the hydraulic system .

Further research may suggest that they use certain manufacturing processes in order to make sure

air never enters a hydraulic system during its use. This may be a topic that I will pursue in a later

log because it will help me to better understand the removal of air present in a hydraulic system.

Appendix

Figure 1: Shows that a small force applied to a small piston creates a greater amount of force on the big piston because of pressure created in the fluids between them.

Figure 2: Shows the model hydraulic crane I created.

Video 1: https://www.youtube.com/watch?v=plkWmxNc82Y

Works Cited

Aleccia, JoNel. Bunk beds cause boo-boos -- and serious injury. 2 June 2008. 7 October 2014. <http://www.nbcnews.com/id/24895552/ns/health-childrens_health/t/bunk-beds-cause-boo-boos-serious-injury/#.VDYOx_ldUuQ>.

Chalupnik, James D. "Hydraulics." World Book Advanced. World Book, 2014. Web.  9 Oct. 2014.

Easy Hydraulic Machines. n.d. 8 October 2014. <http://www.instructables.com/id/Easy-Hydraulic-Machines/>.

Haverdink, William H. "Brake." World Book Advanced. World Book, 2014. Web.  9 Oct. 2014.

Hodanbosi, Carol. Pascal's Principle and Hydraulics. August 1996. 7 October 2014. <http://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/Pascals_principle.html>.

How Hydraulic Jacks Work. n.d. 8 October 2014. <http://www.thomasnet.com/articles/materials-handling/how-hydraulic-jacks-work>.

Kelsey. What is Hydraulic Fluid? 1 October 2014. 7 October 2014. <http://www.wisegeek.com/what-is-hydraulic-fluid.htm>.

Mechanical Advantage. n.d. 8 October 2014. <http://www.merriam-webster.com/dictionary/mechanical%20advantage>.

"Pressure." n.d. revision world. Picture. 8 October 2014.

Reverb:SRAM. n.d. 8 October 2014. <https://www.sram.com/rockshox/products/reverb>.