HYDRAULICS. 



11 



neath an ascending piston, and is drawn 

 upwards by it, as is the case in a pump, 

 the circumstances of pressure will al- 

 ways remain the same, and will be re- 

 gulated only by the perpendicular height 

 and horizontal sectional area of the co- 

 lumn. The working barrel of the pump, 

 or the piston that works in it, will 

 therefore always determine the area of 

 the column : and whether the pipe that 

 carries the water up into it, or upwards 

 from it, be greater or less, the effective 

 force to work the pump will be the 

 same, friction only excepted. 



Notwithstanding the common lifting 

 pump is incapable of raising water from 

 more than 33 feet (or rather 30 feet) 

 below the place where it may be fixed, 

 yet it may be made to deliver water at al- 

 most any required height above its piston 

 by the application of a continued straight 

 pipe instead of the cistern-head shown 

 at o v in the last figure. Thus if that 

 cistern-head and spout be supposed to 

 be taken away, and 20 or 30 feet of close 

 iron pipe to be added to the top of the 

 working-barrel in m, since the water 

 once raised cannot pass downwards 

 again through the valve t in the piston 

 or bucket t n, it must continue to rise 

 with each stroke of the pump, until at 

 length it will flow over the top of the 

 pipe, or through a spout inserted in any 

 part of its side. In this case atmos- 

 pheric pressure has nothing to do with 

 the elevation above the piston, conse- 

 quently it may be earned to any height 

 that the strength of the pump will admit 

 of, but the handle pp (or any other con- 

 trivance by which the pump is w r orked) 

 must be fixed above the top of this pipe, 

 and the piston-rod o must be equal in 

 length to the pipe in order to keep the 

 working-barrel within the limits of at- 

 mospheric pressure, which makes this 

 arrangement of pump inapplicable to 

 very great depths on account of the 

 bending of the piston-rod. Where cast- 

 iron pipes are used, this may be in a 

 great measure prevented by placing 

 small pieces with projecting arms of 

 sufficient length to touch the inside of 

 the pipe at each joint of the piston-rod, 

 or about 10 or 12 feet asunder, when 

 this pump may be used for considerable 

 depths wiih advantage. 



In using pumps to draw muddy or 

 sandy water, it is always advisable to set 

 the bottom of the pump in a close wicker 

 basket or other strainer, because sand 

 and small stones very soon destroy the 

 leather and working parts of any pump ; 



and when pumps are used for hot li- 

 quors, which is the case in many manu- 

 factories, thick hempen canvass must 

 be substituted for leather, unless the 

 valves and piston are made entirely of 

 metal. 



As the above -described pump acts 

 entirely by atmospheric pressure, and 

 is therefore incapable of drawing water 

 from a greater depth than from 30 to 33 

 feet, it will at once appear that it is 

 inapplicable to mines, or those situations 

 in w r hich it may be necessary to bring 

 water from great depths, or to raise it 

 to great elevations. Whenever this re- 

 quires to be done, the third class of 

 pumps or machines must be resorted to, 

 or those which act by mechanical force 

 or compression, instead of atmospheric 

 pressure alone ; and all pumps of this 

 description are very properly denomina- 

 ted Forcing -pumps. Although atmos- 

 pheric pressure is not necessary to the 

 construction of forcing-pumps, yet it is 

 in most cases resorted to for raising the 

 water in the first instance into the body 

 of the pump where the forcing action 

 commences and takes place ; and when 

 so constructed, such pumps are gene- 

 rally called lift and force pumps, and in 

 all the machines of this description the 

 water may be raised to any required 

 height without limit, provided there is 

 sufficient power to work the pump, and 

 the pipes and materials of the machine 

 are strong enough to bear the pressure 

 of the perpendicular column of water. 



Forcing-pumps do not differ mate- 

 rially in construction from the common 

 lifting or household pump already de- 

 scribed ; indeed that pump, by a mere 

 inversion of its parts, may be made into 

 a forcing-pump, that is to say, placing 

 the piston below, and the stop-valve and 

 delivering pipe above, as shown at fig, 

 8, where h h shows the inverted work- 

 ing barrel, and i the inverted piston and 

 rod with a valve opening upwards : k is 

 the stop-valve placed at the top, instead 

 of the bottom of the barrel, and also 

 opening upwards into the rising pipe / /, 

 which may be continued to any required 

 height ; the lower end of the working- 

 barrel is quite open, and must stand in, 

 and be covered with the water it has to 

 raise, so that no suction or feed pipe is 

 necessary to this pump, and the piston 

 t may be worked by a handle and series 

 of levers m, n, o, or in any other conve- 

 nient manner. After the description 

 already given of the common lift-pump, 

 it will be needless to say any thing on 



