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1、Hydraulic MachineFrom: The Columbia Encyclopedia, Sixth Edition Date: 2008 Hydraulic machine that derives its power from the motion or pressure of water or some other liquid. Hydraulic equipment and technology is something that we are all at least passingly familiar with. If we think about it, we kn
2、ow that the principles of hydraulics are applied to make many common machines work. For example hydraulics are used in agricultural equipment, giant earth moving and mining machines, they are used to steer and stabilize giant ocean liners, help airplanes climb and turn, and make the brakes in our ca
3、rs work. So hydraulics can provide great force, are obviously very adaptable and used in all kinds of applications, but how do they actually work?What is this hydraulics stuff?Hydraulics is based on a very simple fact of nature - you cannot compress a liquid. You can compress a gas (think about putt
4、ing more and more air into a tire, the more you put in, the higher the pressure). If youre really strong you can compress a solid mass as well. But no matter how much pressure you apply onto a liquid, it isnt possible to compress it. Now if you put that liquid into a sealed system and push on it at
5、one end, that pressure is transmitted through the liquid to the other end of the system. The pressure is not diminished. Hydraulics is Old StuffThe basic concept of hydraulics is not new. The Greeks understood about using water to provide lift and force, and the name hydraulics come form the Latin w
6、ord for water - “HYDRA“. In the middle Ages, Leonardo da Vinci formulated the basic principle of hydraulics called continuity and Galileo experimented with hydraulics. Hydraulics were even used during the construction of the Eiffel Tower in Paris in the late 1880s. Hydraulic jacks were used to level
7、 the tower and align the metal girders to an accuracy of 1 millimeter。Today most hydraulic systems utilize oil rather than water but the principle is the same. You can compress a liquid, and a force that is applied at one point is transmitted to another point by that incompressible fluid. Because of
8、 its liquid nature, hydraulic systems can transmit force through pipes of any shape and length, so the force can be applied at one central point and transmitted efficiently to another point or to multiple points far away. Think about the master cylinder in you cars brakes and how, by stepping on the
9、 brake pedal, you apply stopping pressure on the brakes on all four wheels.PhysicsBasic physics tells us that we can trade off force for distance in all mechanical systems. In a hydraulic system, we do this by changing the relative size of the pistons at each end of the system. For example, a small
10、piston moving a relatively large distance (say a foot) will exert pressure on a larger piston at the other end. The force will be enough to move a heavy weight a small distance (much less than a foot). Engineers and physicists can calculate exactly how much distance needs to be traveled and the rela
11、tive sizes of the pistons required to move a particular weight. Hydraulic Engines Water falling from one level to a lower one is used to drive machines like the water wheel and the turbine . The difference in height between the highest and the lowest level is called the head。 The amount of work prod
12、uced per pound of falling water is proportional to the head. Water power can be produced in this way from many natural sources, such as waterfalls and dammed rivers.。Where no natural sources are available, an artificial reservoir can be made. When energy is plentiful, it is used to pump water into t
13、he reservoir; the water is then available as a power source to drive turbines when energy becomes scarce. In driving certain industrial hydraulic machines an apparatus called an accumulator is employed to supply high power for short periods of time. One type consists essentially of a cylinder enclos
14、ing a piston loaded with weights. When water is slowly pumped into the cylinder, the piston and weights are forced up to a position where they are held. When they are released, they force the water out of the cylinder rapidly, providing the machine with hydraulic power. Hydrostatic DevicesWater or o
15、il under pressure is commonly used as a source of power for many types of presses, riveting machines, capstans, winches, and other machines. The hydraulic press, or hydrostatic press, was invented by Joseph Bramah and is therefore sometimes called the Bramah press. It consists essentially of two cyl
16、inders each filled with liquid and each fitted with a piston; the cylinders are connected by a pipe also filled with the liquid. One cylinder is of small diameter, the other of large diameter. According to Pascals law , pressure exerted on the smaller piston is transmitted undiminished through the liquid to the surface of the larger piston, which is forced upward. Although the pressure force per unit of area) is the same for both pistons, the total upward force on the larger piston is a
