Crushin' It With Pascal

I wanted to find out how hydraulics are so powerful, so I built a model hydraulic can crusher. A basic hydraulic system consists of a reservoir, pump, actuators and a return valve. Hydraulic forces are the product of pressure and surface area of the actuators. Together, higher pressure and surface area creates a greater hydraulic force.

In my hydraulic system, a pump pulls water from the reservoir through a check valve. A check valve is a special valve that only lets water flow in one direction, often called a one-way valve. When I push down on the pump, the water goes through a second check valve. Once the water is through the second valve, it builds pressure in the system.

Pascal’s Principle states that pressure is equal throughout the entire system. This applies pressure on the actuators making the syringes extend. With just a few pumps, it’s able to crush a can. To retract the actuators, the return valve must be open allowing the water to return to the reservoir.

Hydraulics are used in many types of machinery like back hoes, excavators, jacks and industrial equipment.

I enjoyed learning how hydraulics can make tasks easier, faster and safer.

While waiting for the school bus one morning, I was curious how hydraulics made our family backhoe so strong and powerful. My dad explained that wider actuators generate more force and showed me that some actuators were larger than others. I began to understand that some parts must be stronger than others. The purpose of this project was to investigate how hydraulics generate force and to see if a model hydraulic system built using common items could generate enough force to crush an aluminum soda can. Hydraulics are important in machines like backhoes and excavators, but also in tools like car jacks or things as common as brakes in a car. Many people don’t realize how hydraulics help make modern life possible by making difficult tasks easier, faster and safer.

My research began by learning about basic hydraulic systems. I learned about Pascal’s Principle and the equation . Since the actuators are round, I used the formula for area of a circle, . I also learned that force can be converted to mass through the equation .

Next, I needed to find out how much force is needed to crush an aluminum can. To do this, I carefully placed weights on top of an aluminum can until it crushed. I recorded the last weight it held, and the weight it failed at. I repeated this experiment several times to find an average. I also tested cans with and without imperfections and recorded their data separately. I used this as my desired output force.

To estimate how hard I could squeeze a syringe, I used my fingers and thumb to squeeze a fish scale as hard as I could and recorded the value and used that as my input force. With the formulas above, I estimated that I could crush a soda can using one 30ml pump syringe and two 60 ml actuator syringes.

I sketched a rough layout of how my hydraulic system could work. In my first attempt, I had the two 60ml actuator syringes pushing in opposite directions. I thought this would generate the same force as two actuators pushing in the same direction, but with the benefit of a higher speed. During that experiment, I found that it was much harder than expected to crush the can. I hypothesized that the actuators were cancelling each other out, and I was only getting the force of one actuator. In my second design, I positioned the actuators on the same side and added a third. This time, it was much easier to crush the can.

My research into hydraulic systems and understanding of helped make my experiment a success. I designed a hydraulic system using a water reservoir, two check valves and a syringe as a pump, three larger syringes as actuators and a ball valve as a return valve. I was also able to calculate the actuator sizes and pump sizes needed to generate the required forces to crush an aluminum can.

By retracting the pump syringe, a check valve lets water flow from the reservoir into the syringe. When pumping the syringe, the first check valve prevents the water from returning to the reservoir, forcing it through the second check valve. With the ball valve closed, the water builds pressure in the actuators. As the pressure builds, the actuators begin to extend with force. Opening the ball valve releases the pressure and allows the water to return to the reservoir so you can retract the actuators.

My experiment allows you to use different size pump syringes. Rearranging into shows that a smaller pump syringe will generate higher pressures without any increase in pumping force. This effect is noticeable when switching the syringe sizes while crushing a can.

While it seems easy to generate high pressures and high forces, I noticed that using a smaller pump syringe moved less water with each pump. This means that it takes more pumps and more time to extend the actuators, even though the pressure is higher. If you try to increase force by increasing the area of the actuators, or by adding more actuators, you also increase the volume of water needed to fill and extend them. This also means that it takes more pumps and more time to extend the actuators.

I realized that it is possible to generate high pressures at low speed or low pressures at high speeds, but you can’t get both at the same time. I found that a balance between pressure and speed gave the most practical and enjoyable result.

If I were to expand my project, I would add a pressure gauge to observe how much pressure is reall needed to crush a can. I would also explore methods to measure how much force is being applied by the actuators. I would be interested to see if the actual forces are the same as the calculated forces. I would also like to add a pressure relief valve that would allow the water back to the reservoir if pressure became too high.

I would like to thank four kindhearted people for a multitude of different reasons. The first person I would like to thank would be my mentor / James Gourley (Dad) who helped teach me how to use software such as Inkscape, V Carve, Light Burn, Capcut and Excel. I would also like to thank my mentor for supplying me with videos and taking some pictures. The next person I would like to thank would be my teacher Joanna Martins for proofreading my writing and giving me helpful editing tips. I would also like to thank my Mom (Lisa Hamilton) for helping me with the registration and tech issues. Finally, I would like to thank my neighbours Bill and Linda for providing me with dozens of cans to design, complete and demonstrate my project.

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