Hydraulic Press

4 Key excerpts on "Hydraulic Press"

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  eBook - ePub

  Principles of Hydraulics

  • Horst Walter Grollius(Author)
  • 2017(Publication Date)
  • Books on Demand

    (Publisher)

  system pressures ). Mostly the hydrostatic pressure finds no consideration, because this pressure often is negligible low compared with the system pressures.

  2.4 Hydraulic Press

  The fundamental functionality of the Hydraulic Press should be explained on the basis of Figure 2.5 .

  Figure 2.5: For explaining the Hydraulic Press

  The influence of the hydrostatic pressure remains disregarded. The pistons of the Hydraulic Press are sealed by freely of friction controlled pistons without leakage.

  The pressure p acts according to the law of Pascal on all places of the fluid. Therefore the pressure p acts also on the area A 2 of the piston 2. With

  we obtain

  With equation (2.21 ) the principle of force transmission can be made clear. For example: A 2 = 10 · A 1 F 2 = 10 ·F 1

  With the movement of the piston 1 around the way s 1 the volume V 1 = A 1 · s 1 is displaced. The piston 2 is thereby moved around the way s 2 upwards. It is

  We obtain

  With equation (2.23 ) the principle of way transmission can be made clear. For example: A 2 = 10 · A 1

  2.5 Pressure Transmission

  The principle of pressure transmission should be explained on the basis of Figure 2.6 .

  Figure 2.6: For the explanation of the pressure transmission

  Both freely of friction controlled and without leakage sealed pistons (areas A 1 and A 2 ) are connected by a pole firmly with each other.

  The pressure p 1 acts at the surface A 1 . The piston 1 attacking force is therefore F = p 1 · A 1 . For reasons of the static balance the force F attacks the piston 2 too. The pressure at the piston surface A 2 is therefore It is

  So we get

  With equation (2.26 ) the principle of pressure transmission can be made clear. For example: A 1 = 2 · A 2 p 2 = 2 · p 1

  2.6 Hydraulic Work, Hydraulic Power, Efficiencies

  For explaining the term hydraulic work Figure 2.5 has to be looked. The piston 1 is moved with the force F 1 along the way s 1 . It is done the hydraulic work

  During this process the piston 2 is moved with the force F 2 along the way s 2

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  eBook - ePub

  Fluid Power Dynamics

  • R. Keith Mobley(Author)
  • 1999(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Figure 1-2 illustrates the transmission of forces through liquids. For Pascal’s law to become effective for practical applications, a piston or ram confined within a close tolerance cylinder was needed. It was not until the latter part of the eighteenth century that methods were developed that could manufacture the snugly fitted parts required to make hydraulic systems practical.

  Figure 1-2 Transmission of forces.

  This was accomplished by the invention of machines that were used to cut and shape the necessary closely fitted parts, and particularly by the development of gaskets and packing. Since that time, components such as valves, pumps, actuating cylinders, and motors have been developed and refined to make hydraulics one of the leading methods of transmitting power.

  USE OF HYDRAULICS

  The Hydraulic Press, invented by Englishman John Brahmah, was one of the first workable machines that used hydraulics in its operation. It consisted of a plunger pump piped to a large cylinder and a ram. This press found wide use in England because it provided a more effective and economical means of applying large, uniform forces in industrial uses.

  Today, hydraulic power is used to operate many different tools and mechanisms. In a garage, a mechanic raises the end of an automobile with a hydraulic jack. Dentists and barbers use hydraulic power to lift and position their chairs. Hydraulic doorstops keep heavy doors from slamming. Hydraulic brakes have been standard equipment on automobiles since the 1930s. Most automobiles are equipped with automatic transmissions that are hydraulically operated. Power steering is another application of hydraulic power. Construction workers depend upon hydraulic power for their equipment. For example, the blade of a bulldozer is normally operated by hydraulic power.

  Operation of Hydraulic Components

  To transmit and control power through pressurized fluids, an arrangement of interconnected components is required. Such an arrangement is commonly referred to as a system. The number and arrangement of the components vary from system to system, depending on the particular application. In many applications, one main system supplies power to several subsystems, which are sometimes referred to as circuits. The complete system may be a small, compact unit or a large, complex system that has components located at widely separated points within the plant. The basic components of a hydraulic system are essentially the same, regardless of its complexity. These seven components, which must be in every hydraulic system, are as follows:

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  Discoveries and Inventions of the Ninteenth Century

  • Robert Routledge(Author)
  • 2018(Publication Date)
  • Routledge

    (Publisher)

  It would be more precise to say, that what is gained in force is lost in space; or, that no machine, whatever may be its nature or construction, is of itself capable of doing work. The “mechanical powers,” as they are called, can do but the work done upon them, and their use is only to change the relative amounts of the two factors, the product of which measures the work, namely, space and force. Pascal himself, in connection with the passage quoted above, clearly points out that in the new mechanical power suggested by him in the Hydraulic Press, “the same rule is met with as in the old ones—such as the lever, wheel and axle, screw, &c.—which is, that the distance is increased in proportion to the force; for it is evident that as one of the openings is a hundred times larger than the other, if the man who pushes the small piston drives it forward 1 in., he will drive backward the large piston one-hundredth part of that length only.” Though the Hydraulic Press was thus distinctly proposed as a machine by Pascal, a certain difficulty prevented the suggestion from becoming of any practical utility. It was found impossible, by any ordinary plan of packing, to make the piston fit without allowing the water to escape when the pressure became considerable. This difficulty was overcome by Bramah, who, about the end of last century, contrived a simple and elegant plan of packing the piston, and first made the Hydraulic Press an efficient and useful machine. Fig. 166 is a view of an ordinary Hydraulic Press, in which a is a very strong iron cylinder, represented in the figure with a part broken off, in order to show that inside of it is an iron piston or ram, b, which works up and down through a water-tight collar; and in this part is the invention by which Bramah overcame F IG. 165. Collar of Hydraulic Cylinder. the difficulties that had previously been met with in making the Hydraulic Press of practical use. Bramah’s contrivance is shown by the section of the cylinder, Fig

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  Discoveries and Inventions of the Nineteenth Century

  • Robert Routledge(Author)
  • 2018(Publication Date)
  • Routledge

    (Publisher)

  Fig. 168 , are filled with concrete, on which the feet of the hydraulic cylinders rest. The outer columns support no weight, but act merely as guides for the crossheads attached to the plungers. The height of the columns is 68½ ft., and a wrought I ¡I iron framed platform connects the columns at I il the top. In order that any inequalities in the height of the rams may be detected, a scale is painted on each column, to mark the positions of the crossheads. The hydraulic cylinders, which are within these columns, have solid rams of 10 in. diameter, with a stroke of 25 ft., and on the tops of these are fastened the crossheads, 7½ ft long, made of wrought iron, and supporting at the ends bars of iron, to the other ends of which the girders of the platform are suspended. The girders are, therefore, sixteen in number, and together form a gridiron platform, which can be raised or lowered with the vessel upon it. The thirty-two hydraulic cylinders were tested at a pressure of more than 3 tons per square inch. The water is admitted immediately beneath the collars at the top (this being the most accessible position) by pipes of only ½ in. diameter, leading from the force-pumps, of which there are twelve, of 17/8 in. diameter, directly worked by a fifty horse-power steam engine. The presses are worked in three groups—one of sixteen, and two of eight presses,—so arranged that their centres of action form a sort of tripod support, and the presses of each group are so connected that perfect uniformity of pressure is maintained. The raising of a vessel is accomplished in about twenty-five minutes, by placing below the vessel a pontoon, filled in the first instance with water, and then raising the pontoon with the vessel on it, while the water is allowed to escape from the pontoon through certain valves; then when the girders are again lowered, the pontoon, with the vessel on it, remains afloat. Thus in thirty minutes a ship drawing, say, 18 ft. of water is lifted on a shallow pontoon, drawing, perhaps, only 5 ft., and the whole is floated to a shallow dock, where, surrounded with workshops, the vessel, now high and dry, is ready to receive the necessary repairs. The number of vessels which can thus be docked is limited only by the number of pontoons, and thus the same lift serves to raise and lower any number of ships, which are floated on and off its platform by the pontoons. With a pressure in the hydraulic cylinders of about 2 tons upon each square inch, the combined action of these thirty-two presses would raise a ship weighing 5,000 tons.

  FIG . 168.—Sedion of Column.

  Hydraulic power has been used not only for graving docks, as shown in the, ebove figures, but also for dragging ships out of the water up an inclined plane. The machinery for this purpose was invented by Mr. Miller for hauling ships up the inclined plane of “ Martin’s slip,” at the upper end of which the press cylinder is placed, at the same slope as the inclined plane, and the ship is attached, by means of chains, to a crosshead fixed on the plunger. Hydraulic power has also been used for launching ships, and the launch of the Great Eastern

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