Hydraulic Pneumatic Earth Mover
When people mention the word “hydraulics”, they could be talking about pumps, turbines, hydropower, erosion, or river channel flow. The term “hydraulics” means using fluid power, and deals with machinesand devices that use liquids to move, lift, drive, and shove things around.
Liquids behave in certain ways: they are incompressible, meaning that you can’t pack the liquid into a tighter space than it already is occupying.
However, if you add pressure to one end of the tube (by blowing into the tube), the water level will rise on the opposite side. If you decrease the pressure (by blowing across the top of one side), the water level will drop on the other side.
In physics, this is defined through Pascal’s law, which tells us how the pressure applied to one surface can be transmitted to the other surface. As liquids can’t be squished, whatever happens on one surface affects what occurs on the other. Examples of this effect include siphons, water towers, and dams. Scuba divers know that as they dive 30 feet underwater, the pressure doubles. This effect is also show in hydraulics – and more importantly, in the project we’re about to do!
But first, let’s understand what’s happening with liquids and pressure:
Here’s an example: If you fill a glass full to the brim with water, you reach a point where for every drop you add on top, one drop will fall out. You simply can’t squish any more water molecules into the glass without losing at least the same amount. Excavators, jacks, and the brake lines in your car use hydraulics to lift huge amounts of weight, and the liquid used to transfer the force is usually oil at 10,000 psi.
Air, however, is compressible. When car tires are inflated, the hose shoves more and more air inside the tire, increasing the pressure (amount of air molecules in the tire). The more air you stuff into the tire, the higher the pressure rises. When machines use air to lift, move, spin, or drill, it’s called “pneumatics”. Air tools use compressed air or pure gases for pneumatic power, usually pressurized to 80-100 psi.
Different systems require either hydraulics or pneumatics. The advantage to using hydraulics lies in the fact that liquids are not compressible. Hydraulic systems minimize the “springy-ness” in a system because the liquid doesn’t absorb the energy being transferred, and the working fluids can handle much heavier loads than compressible gases. However, oil is flammable, very messy, and requires electricity to power the machines, making pneumatics the best choice for smaller applications, including air tools (to absorb excessive forces without injuring the user).
We’re going to build our own hydraulic-pneumatic machine. Here’s what you need to do:
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