HYDRAULICS. 



pump is attached by a swivel -joint, 

 while the whole revolves on two end- 

 bearings or pivots xy. The conse- 

 quence of this is, that while the piston- 

 rod b connected to the crank w-is at the 

 very lowest point or bottom of its stroke, 

 the piston-rod a with its crank u is very 

 nearly at its greatest height, but the rod 

 z and the crank v are horizontal and in 

 the middle of their stroke: the pump 

 connected w ith v would therefore be the 

 only active one in the present state of 

 things, but if the crank is supposed to 

 be in motion, before the rod z gets to 

 the bottom, b will have begun its as- 

 cending and a its descending stroke, so 

 that by this contrivance one pump is 

 always" brought into effective action just 

 before another ceases to act, and thus a 

 constant stream is produced. To give 

 the triple crank its most perfect action, 

 the three cranks or arms should make 

 angles of 120 degrees with each other, 

 or, when viewed from either end x or y t 

 should stand like the three radii cde 

 drawn separately under the last figure. 



In most cases of raising water, the 

 forcing-pump may be resorted to with 

 advantage, particularly when the pump 

 is of large dimensions, and the height 

 to which the water is to be raised is 

 great, for this might endanger the dis- 

 tortion or breaking of the crank above- 

 described. The forcing-pump is like- 

 wise generally used in conjunction with 

 an air-vessel, or strong metallic box to 

 contain condensed air, the spring or 

 elasticity of which enables this pump to 

 produce all the beneficial effects of a 

 constant current with one, or at most 

 two working-barrels, instead of the 

 three that are necessary with the triple 

 crank, and thus a considerable portion 

 of friction is avoided. 



The forcing-pump is made in two 

 forms, suited to the situation and cir- 

 cumstances under which it has to work. 

 The simplest and best construction is 

 shown at fig. 10. It consists of a 

 truly-bored cylindrical working-barrel 

 ff t the top of which is quite open to 

 admit the solid piston f , which works in 

 it in a perfectly air and water tight 

 state, by means of the lever or handle 

 gg, or "any other or more convenient 

 application of power : h is the feeclinir- 

 pipe, dipping into the water to be raised 

 as in any other pump, and this pipe may 

 of course be made of any length under 

 33 feet ; k is the stop-valve, covering 

 the top of the feed-pipe, and permitting 

 \vater to rise into the working-barrel as 



the piston ascends, but not permitting it 

 to return again : so that whenever the 



fig. 10. 



piston is raised by its handle g, the bar- 

 rel will be filled with water forced up 

 the pipe h by atmospheric pressure ; and 

 when the piston descends again, since 

 there is no valve in it to permit the 

 water to pass through it, it will be forced 

 up the lateral pipe'/ (opening into the 

 bottom of the working-barrel,) and 

 through the valve />?, which prevents its 

 returning back again, so that it is con- 

 strained to find its way up the rising 

 pipe pp fixed above the valve m, and 

 this pipe may be continued to any re- 

 quired heisrht without regard to the 

 pressure of the atmosphere, since the 

 ascent of the water does not depend 

 upon its action, but upon the mechani- 

 cal force that is applied to the handle g 

 to depress the piston. While the piston 

 rises to fill the working-ban-el, the valve 

 m will be shut, and of course all motion 

 of the fluid in the pipe p p will cease, 

 and hence the use of the air-vessel n 

 for it will be seen that the pipe pp is 

 not joined on immediately above the 

 valve m, but that it passes" throuo-h the 

 top of an air-tight copper or other hol- 

 low vessel n, and proceeds nearly to the 

 bottom of it. Air being a lighter fluid 



