HYDRAULIC ENGINES. 59 
the crank is applied at f to the axle of the pinions, m, and ¢ is thrown out 
of gear by releasing the detent, g. The frame, p, turns on a centre pin, 2, 
and is supported on six rollers, A, which run in a circular track on the 
truck, xr. The latter is mounted on four wheels, ¢, which can be set in any 
direction by means of the bolts, % When the whole crane is to be moved, 
it is done by means of blocks and tackle, as the application of levers under 
the truck would disturb the equilibrium of the machine. 
Ul. HYDRAULIC ENGINES. 
Hydraulic engines are machines by the aid of which water is raised or 
thrown from a lower to a higher point. We proceed to consider the usual 
kinds of hydraulic engines under their respective heads. 
1. Pumps. 
We have in general three classes of pumps, viz. suction or lift pumps, 
Forcing pumps, and double action pumps, which combine the principles of ~ 
the two former. 
A lift-pump (pl. 18, fig. 1) consists of a straight or bent pipe as, the 
suction-pipe, extending below the surface cd of the water, enlarged at the 
lower end, and generally provided with a strainer or perforated cap, ab, to 
exclude impurities ; joined to the upper end of the suction-pipe is a pipe 
cp, which is generally larger than the former, and must be bored truly 
eylindrical, in order to allow the box e to fit perfectly water-tight and move 
with as little friction as possible. At the junction of the two pipes is placed 
the valve a, the swction-valve, which in its simplest form moves on a leather 
hinge, opening upwards. The box e is perforated and provided with a 
similar valve Fr, also opening upwards. Hux is the pitman, which is moved 
up and down by means of the bent lever or pump-handle grim. Frequently 
there is a contrivance to insure the rectilinear motion of the piston-rod, or 
at least there is a joint at 3, which allows the portion su to remain nearly 
perpendicular during the reciprocating motion. The action of this machine 
is quite simple: at the commencement the suction-pipe is filled with water 
to e¢ (the level of the surrounding water), and the space between ez and the 
bucket ¢ is filled with atmospheric air. As the bucket rises the air between 
it and the suction-valve a will expand, and the latter will be opened by the 
greater pressure from below; when the bucket has reached its highest posi- 
tion, 41, the water will have risen to a height, mn, at which its pressure 
added to that of the rarefied air m the space klmn equals that of the 
exterior air; the suction-valve will now be closed by its own weight. By 
the descent of the bucket the air between it and the valve a is condensed 
again until its pressure begins to exceed that of the exterior air, when the 
bucket-valve r will open and allow the air to escape. By repeating the 
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