HYDRODYNAMICS. 



19 



der whose base is the area of a cross section of the 

 boJy of the pump, and height the play of the piston. 

 Thus, if the diameter of the cylinder of the pump be 

 4 inches, and the play of the piston 3 feet, then, by 

 mensuration, we have to find the content of a cylinder 

 4 inches diameter, and 3 feet high now, 4 inches is 

 the i of a foot, or -333, hence, -333' x -7854 = 

 110999 X -7854 = -08796 = the area of the cross 

 section of the cylinder in square feet; hence, -08796 

 X 3 = -2639 = the content of the cylinder in cubic 

 feet = the quantity of cubic feet of water discharged 

 by one stroke of the piston. Now, a cubic foot of 

 water weighs about 63-5 Ibs. avoirdupois, wherefore, 

 2639 x 63-5=16-756 Ibs. avoirdupois and an im- 

 perial gallon is equal to 10 Ibs. of water; whence, 

 dividing the above number 16-756 by 10, we get the 

 number of ale gallons = 1-6756. The piston, 

 throughout its ascent, has to overcome a resistance 

 equal to the weight of a column of water, having 

 the same base as the area of the piston, and a 

 height equal to the height of the water in the body 

 of the pump above the water in the well. 



The lifting pump. This pump like the suction 

 pump has two valves and a piston, both opening 

 upwards; but the valve in the cylinder instead of 

 being placed at the bottom of the cylinder is placed 

 in the body of it, and at the height where the water 

 is intended to be delivered. The bottom of the 

 pump is thrust into the well a considerable way, and 

 if the piston be supposed to be at the bottom, it is 

 plain, that as its valve opens upwards, there will be 

 no obstruction to the water rising in the cylinder to 

 the height which it is in the well ; for, by the prin- 

 ciples of hydrostatics, water will always endeavour 

 to come to a level. Now when the piston is drawn 

 up, the valve in it will shut, and the water in the 

 cylinder will be lifted up ; the valve in the barrel 

 will be opened and the water will pass through it, 

 and cannot return as the valve opens upwards ; 

 another stroke of the piston repeats the same pro- 

 cess, and in this way the water is raised from the 

 well : but the height to which it may be raised is not 

 in this as in the suction pump limited to thirty-two 

 feet. To ascertain the force necessary to work this 

 pump, we are to consider that the piston lifts a 

 column of water whose base is the area of the pis- 

 ton, and height the distance between the level of the 

 water in the well and the spout, at which the water 

 is delivered. 



The forcing pump remains to be considered. The 

 piston of this pump lias no valve, but there is a valve 

 at the bottom of the cylinder the same as seen at A. 

 In the side of the cylinder, and im- 

 mediately above the valve B, there 

 is another valve A opening out- 

 wards into a tube, which is bent 

 upwards to the height H at which 

 the water is to be delivered. When 

 the piston is raised, the valve in the 

 bottom of the pump opens, and a 

 vacuum being produced, the water 

 is pressed up into the pump on the 

 principle of the sucking pump. But 

 when the piston is pressed down, 

 the valve A at the bottom shuts, 

 and the valve B at the side which 

 leads into the ejection pipe opens, and the water is 

 forced up the tube. When the piston is raised again 

 the valve B shuts, and the valve A opens. The 

 same process is repeated, and the water is thrown out 

 at every descent of the piston, the discharge therefore 

 is not constant. It is frequently required that the 

 discharge from the pump should be continuous, and 

 this is effected by fixing to the top of the eduction 



u 



pipe an air vessel. This air ves- 

 sel consists of a box AB, in the 

 bottom of which there is a valve C 

 opening upwards into the box. 

 This valve covers the top of the 

 eduction pipe D. A tube, E, is 

 fastened into the top of the box, 

 which reaches nearly to the bottom 

 of the box, it rises out of the box, 

 and is furnished with a stop cock. 

 If the stop cock be shut, and the 

 water be sent by the action of the pump into the 

 air vessel, it cannot return because of the shutting 

 of the valve at the bottom of the box ; and because 

 of the space occupied by the water, the air in the 

 box is condensed, and will consequently exert a pro- 

 portionate pressure on the water in the air vessel, 

 and force it higher up the tube E. 



4. The fourth class of hydraulic machines for rais- 

 ing water, consists of such engines as act either by 

 the weight of a portion of the water which they have 

 to raise, or of any other water that can be used for 

 such purpose, or by its centrifugal force, momentum, 

 or other natural powers; and this class, therefore, 

 includes some very beautiful and truly philosophical 

 contrivances, too numerous for us to describe. The 

 Hungarian machine, the centrifugal pump, and the 

 water-rani, are among the number. 



The large pipe AB called the body of the ram, 

 passes through the side of the reservoir PQ, from 

 which the fall of water is obtained. It has a trumpet 

 mouth at one end A, and at the other end an opening 

 HH, which can be closed by valves C or D. When 

 these valves are open, the water will issue at II H 

 with a velocity due to the height AP; but when the 

 internal valve C is closed, as in the figure, the water 

 is prevented from issuing. When the valve C opens, 

 it descends into the position shown by the dotted lines 

 GG, being guided between three or four stems g g, 

 which have hooks at the lower ends for supporting 

 the valves. In this case the water has a free passage 

 between these stems, and the width of the passage 

 can be increased or diminished by the screws with 



which the stems are fixed. The valve C is made of 

 metal, and has a hollow cup or dish of metal at- 

 tached to its lower surface. The seat HH of the 

 valve is wider than the diameter of the pipe AB. 

 It consists of a short cylinder or pipe screwed by its 

 f land i h h into the opening of the upper surface of 

 the head R of the ram; and the cylinder is so formed 

 as to have an inverted cup or annular space t f round 

 the upper part of it for containing air, which cannot 

 escape when it is compressed by the water. A small 

 pipe k I, leading from this annular space to the open 

 air, is furnished with small valves, k, I, one of which, 

 k, opens inwards to admit the air into f, t, but to 

 prevent its return, while the other valve, /, admits a 

 certain quantity of air, and then shuts and prevents 

 any farther entrance. The valve D is exactly the 

 same as C, only it descends as in the figure when 

 it shuts, and rises when it opens. The upper part 

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