. Elements of technology :. he airnearest the joint is compressed into a space much smaller thanthat which it occupied at its entrance, so that where the heightis considerable, it becomes advisable to admit a larger portionof air than would naturally fill half the coil. This lessens thequantity of water raised, but it lessens also the force required toturn the machine. The joint should be conical, in order thatit may be tightened when it becomes loose, and the pressureought to be removed from it as much as possible. The loss ofpower, supposing the machine well constructed, arises onlyfrom the
. Elements of technology :. he airnearest the joint is compressed into a space much smaller thanthat which it occupied at its entrance, so that where the heightis considerable, it becomes advisable to admit a larger portionof air than would naturally fill half the coil. This lessens thequantity of water raised, but it lessens also the force required toturn the machine. The joint should be conical, in order thatit may be tightened when it becomes loose, and the pressureought to be removed from it as much as possible. The loss ofpower, supposing the machine well constructed, arises onlyfrom the friction of the water on the pipes, and the friction ofthe wheel on its axis; and where a large quantity of wateristo be raised to a moderate height, both of these resistances maybe rendered inconsiderable. But when the height is very great,the length of the spiral must be much increased, so that theweight of the pipe becomes extremely cumbersome, and causesa great friction on the axis, as well as a strain on the ARTS OF CONVEYING WATER. 313 Centrifugal Pump.—The centrifugal force, has sometimesbeen employed, in conjunction with the pressure of the atmos-phere, as an immediate agent in raising water, by means of arotary pump. The machine called a centrifugal pump, con-sists of a vertical pipe, capable of revolving round its axis, andconnected above with a horizontal pipe, which is open at one,or at both ends, the whole being furnished with proper valvesto prevent the escape of the water, when the machine is atrest. As soon as the rotation becomes sufficiently rapid, thecentrifugal force of the water in the horizontal pipe causes itto be discharged at the ends, its place being supplied by meansof the pressure of the atmosphere on the reservoir below,which forces the water to ascend through the vertical pipe. Thismachine may be so arranged, that, according to theory, very lit-tle of the force applied is lost; but it Fig. failed of producing in practice avery a
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