— = 
SOME HYDRAULIC PRESSURE MACHINES 527 
of the cylinder. The space round the pump in the casing forms a cistern 
for the water. A spindle, one end of which passes through the casing, 
carries at that end the hand lever, and inside the casing it carries a short 
crank, the free end of which works in a rectangular slot formed in the 
plunger of the pump. By this arrangement the oscillation of the lever 
causes the reciprocation of the plunger. The suction valve of the pump 
is at the side, and tho delivery valve at the bottom of the pump. The 
valves are loaded with light spiral springs. 
When the lever is worked the pump takes in water from the cistern 
and delivers it into the cylinder above the ram, and thus causes the 
cylinder and the load on it to rise. During the operation of raising the 
load the lowering screw 
must be screwed up tight. 
The inner end of the lower- rams . F. 
ing screw is conical, and Fi ‘\ 
forms a valve which, when : [0 ' } 
shut, closes the passage y ’ 
between the cylinder and . LY 
cistern outside the pump. eee 
To lower the cylinder the A Bsa D 
lowering screw is un- 
screwed, and the water 
may then flow freely from 
the cylinder to the cistern. 
When the jack is in 
use the air screw at the 
top should be slackened. ” 
Overlifting is prevented by 
the hole H in the cylinder 
allowing the water to 
escape when the proper 
lift is exceeded. Rotation 
of the cylinder on the ram sg 
is prevented by a key 
secured in the cylinder at 
the lower end by a set 
screw; this key fits in a 
keyway extending nearly 
the whole length of the 
ram. 
457. Hydraulic Crane. Cc 
—Comparing the principal —-4+- 
part of the mechanism of |,°:/ \" t 
a hydraulic crane with | 0o/!, : HT) 
the ordinary “block and nA) : ms | 
tackle.” In the block and he hs | 
tackle one force acting on ~ a a 
the “fall” of the, rope 
overcomes a greater by Fia. 840. 
bringing the two blocks 
closer together. In the hydraulic crane the action is reversed; the two 
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