. Elements of technology :. piston, with acollar of loose and elastic leather, is preferable to those of amore complicated structure. The pressure of the water on theinside of the leather makes it sufficiently tight, and the frictionis inconsiderable. In some pumps the leather is omitted, forthe sake of simplicity, the loss of water being compensated bythe greater durability of the pumps ; and this loss will be thesmaller in proportion as the motion of the piston is more rapid. Hydrostatic Press.—This powerful machine is essentially aforcing pump, aided in its action by the well known properti
. Elements of technology :. piston, with acollar of loose and elastic leather, is preferable to those of amore complicated structure. The pressure of the water on theinside of the leather makes it sufficiently tight, and the frictionis inconsiderable. In some pumps the leather is omitted, forthe sake of simplicity, the loss of water being compensated bythe greater durability of the pumps ; and this loss will be thesmaller in proportion as the motion of the piston is more rapid. Hydrostatic Press.—This powerful machine is essentially aforcing pump, aided in its action by the well known propertiesof hydrostatic pressure. It appears to have been invented byPascal, previously to 1664, and recommended by him as a newmechanical power. It was, however, practically lost sight of,till it was reinvented by Mr Bramah, more than a century af-terwards. In this press the water is forced, by a small pump,into a strong iron cylinder, in which it acts on a much largerpiston; consequently this piston is urged by a force as much. ARTS OF CONVEYING WATER. greater than that which acts on the firstpump rod, as its surface is greater thanthat of the small one. In Fig. 10, thewater is forced by the pump A throughthe pipe B, into the cylinder C, inwhich it acts very powerfully upon thelarge piston D, and raises the bottomof the press E. The upward force,by which the material above E is com-pressed, exceeds the force which is applied to the pump, asmuch as the surface of the piston D, exceeds that of the pistonof the pump. Tn practice, the cylinder C requires to be mademuch thicker than here represented. Lifting Pump.—Where the height through which the wateris to be raised is considerable, some inconvenience might arisefrom the length of the barrel through which the piston rod of asucking pump would have to descend, in order that the pistonmight remain within the limits of atmospheric pressure. Thismay be avoided by placing the moveable valve below the fixedvalve, and introducing the pis
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