60 . TECHNOLOGY. 
motion the water will be caused to rise successively in the suction-pipe, and 
will reach the valve a, open it, and arrive at the bucket. In descending 
through the water the bucket-valve will be opened, and the water will 
ascend through it, while the pressure will keep the suction-valve closed : 
on rising, the bucket-valve will close, the bucket lifting up the water in its 
ascent, while the pressure of the atmospheric air will force the water in the 
suction-pipe to follow the bucket to its highest position. By the continued 
play of the bucket the water will thus finally be raised to a reservoir, EE, 
at the top of the pump, whence it is discharged by spouts or cocks. 
In this pump the water is raised entirely by the ascent of the bucket and 
the pressure of the atmospheric air. When the height, ge, of the bucket in 
its lowest position above the level of the water, cd, exceeds that of a column 
of water the pressure of which equals that of the atmosphere, then the 
water will not follow the bucket in its ascent, and cannot, therefore, be 
raised above it. The greatest height at which the bucket may therefore be 
placed above the level of the water to be raised is 32 feet, the height of the 
above column. In practice this height will be diminished by 2 or 3 feet, 
as the development of air contained in the water and the want of a perfectly 
air-tight fit of the piston will not allow a perfect vacuum to be formed. 
A forcing pump in its simplest form is represented in jig. 2. The cylin- 
* der aB, immersed in the water, is closed at the bottom by the valve f, and 
communicates by the valve p with the pipe pz, through which the water is 
forced to the required beight. The solid piston or plunger, c, has no valve, 
and is here moved by means of a lever of the second kind. When the 
plunger rises the water will ascend into the cylinder by its own pressure 
and that of the air; as the plunger begins to descend, the pressure will 
close the valve 7 and open pv, through which the water will be forced into 
the pipe pr. As the plunger ascends again the valve p will be closed by 
the pressure of the water in DE, which is thus prevented from returning into 
the cylinder. If the plunger in its highest position is below the surface of 
the exterior water, the pump will act independent of the pressure of the air, 
and is then a forcing-pump, properly so called. | 
A double action pump is one in which the cylinder is elevated above the 
level of the water, communicating with it by a suction-pipe. This is a kind 
of pump very frequently employed to raise water to great elevations. A 
simple lift-pump, however, may also be employed to raise water to a 
considerable height. 
As an example of this kind jig. 3 represents Stephenson’s pump for wells. 
A is the surface of the ground ; BB the wall of the well in which the water- 
level is below c. pb is the pump-handle by which the pitman @ is worked: 
the latter consists of wooden rods, joined together by iron fastenings, as 
shown in jig. 6. All the pipes are of wood; the cylinder © has a brass 
lining, intended to diminish the friction of the bucket d ; 7’ is the suction- 
valve. The upper end of the cylinder is closed by a metal cover, g (jigs. 4 
and 5), which has a stuffing-box in the centre for the iron piston-rod, A ; 
k (fig. 3) is a guide which keeps the piston-rod in a vertical position. The 
lift-pipe F consists of as many pieces as are required to carry the water 
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