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How Hydraulic Machines Work

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"How Hydraulic Machines Work"
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Hydraulics constitute one of the greatest inventions known to modern lifting machinery. Utilizing a surprisingly basic and simple concept, hydraulics can perform some rather incredible feats of strength, allowing modern machines to heft great weights in the service of mankind.

Hydraulics are everywhere. They're in construction vehicles, like cranes and bulldozers. They're in lifts, like those found in a garage for raising cars under maintenance. They're in exercise equipment. They're in hand pumps. They're in anything that needs to perform some kind of lifting, and plenty others that require a lot of force, and they do their jobs well. So how do they work?

The answer is found in the concept of liquid mechanics, and how they can be applied to lifting force. Hydraulics begin with a rather basic idea: that a liquid, pushed in one direction, will move in another direction. You can see this effect at work every time you press down on water: it ripples out from your hand before you penetrate the surface. Liquid does show some resistance before giving way.

Hydraulics take this redirection and controls it, using that force against another object. In its most basic form, hydraulics employs two pistons fitted into a pipe filled with a liquid. One of those pistons pushes down on the liquid in the pipe, which forces the liquid to rise against the second piston. This pushes that piston up with the same force exhibited by the first piston, thanks to the nature of the liquids used, as hydraulics always employ incompressible liquids like oil. The oil needs to make space for itself, and so the second piston must get out of the way. This piston is connected to whatever device in the machine requires pushing or lifting power, making the machine run.

The secret behind the superior force provided via hydraulics stems from the size of the pistons and the size of the cylinders through which they're pushing the liquid. Two sets of pistons in same-size cylinders will have the same amount of force operating between them. By changing the size of the cylinders relative to one another, however, engineers can either multiply or divide the amount of force that pushes the second cylinder. A long, thin cylinder with a small piston will send a great deal more force to the second cylinder, which contains a much wider piston, over a longer period of time. This principle is known as trading distance for force, and can work in the opposite direction as well (trading force for distance).

The only downside of hydraulics is their requirement for operation. Because they require an incompressible liquid like ever-pricey oil, hydraulic equipment is often expensive to maintain and operate. Large machines, like construction vehicles, often require upwards of 100 gallons of hydraulic oil in their tank at a given time to work at peek efficiency. This makes their use quite costly, and so it's much to their benefit that hydraulics allow for quick, powerful action.

Want to see simple hydraulics in work? Here's a video of a simple wooden hydraulic machine, available at Or, for something more complex, here's a video on how riding lawnmowers work, thanks to a hydraulics system.

More about this author: Matt Bird

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