HYDRAULIC ENGINES. 63 
the pin e will push the lever, n', », into its former position, carrying with it 
the pistons d and d’, and cutting off the communication of the water below 
m with the main pipe. The downward pressure on L exceeding the upward 
pressure on K, they will descend again to the position of jig. 15, the water 
below m being expelled though ¢, oc, and ¢’, into n, when everything is 
again in the position first assumed. 
The two small cut-off pistons, d@ and d’, are of block tin. The alternating 
pistons, K, L, and m, consist each of brass cylinders with a ring of block tin, 
which, being soft and elastic, serves as packing. The counter-piston, s, has 
the same construction. The main piston, tT (jigs. 15, 18, and 19), consists 
of a cylindrical piece of brass (shaded in jig. 19) encircled by two rings, s, s, 
of block tin, which are sufficiently elastic to expand a little when a pressure 
is exerted from within, and to contract again when the pressure ceases. 
This property is made use of by means of the small tubes, z’, z', which com- 
municate with circular grooves in the brass body under the middle of the 
rings. During the descent of the piston the water entering the grooves will 
press the rings outwards and produce a perfect packing, while during the 
ascent the pressure is in a great measure relieved, allowing the wings 
to contract and experience very little friction. The plunger, vu, consists of 
disks of leather saturated with oil; the manner of putting them together is 
seen in fig. 19. A better construction is shown in jig. 20, where it consists 
of two different layers of leather disks, the upper set forming the plunger, 
and the lower set, of less diameter, receiving the blow of the piston on the 
plate, y. The piston-rod, s’, has a ball and socket-joint, as is seen in jig. 19, 
which also shows the connexion of rand v. The piston-rod, £7, also has 
a ball and socket-joint at r. #%g. 17 represents a horizontal section along 
the line, 3,4, in fig. 15, of the forcing pump and valve chamber; jig. 16 
a similar section along the line, 1,2, in jig. 15. 
A second hydraulic engine of this kind is represented in pl. 13, jig. 13. 
It was built by Jordan in the mine of Clausthal, in the Hartz, and was 
completed in 1835, together with another similar one, which works in the 
same shaft. The main piston has a diameter of 17 inches, and is driven by the 
hydrostatic pressure of a column of water 688 feet in height. The operation 
of this machine is similar to that just described, and will be readily under- 
stood. Eis the main pipe, 6 inches in diameter; 0 m v are the alternating 
pistons by which the driving-column is cut off and let on; Tis the main 
cylinder in which the piston is driven upwards by the pressure of the water ; 
H is the back-water pipe through which the spent water is carried off; h is 
a double stop-cock, which opens or cuts off the communication of the pipes 
E and H with the cylinder uv, by means of the tubes 1, 1’, and Lv”, which have 
a diameter of { of an inch. The figure represents the machine just after 
the completion of the upward stroke ; the communication of the main pipe 
with the cylinder rT is cut off by the piston-valve m, and the main piston- 
rod p will descend, and by its own weight and that of the long piston-rod 
ce, which descends to the bottom of the shaft, will force the spent water in t 
up the back-water pipe u to an elevation of 80 feet, where it flows off. In 
descending, the projection ® operating against the angular arm a’, causes 
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