+---------+-------------+-------------+------+ | WATER | THICKNESS. | DIAMETER. |WEIGHT| |PRESSURE.| | | PER | | | | | YARD.| +---------+-------+-----+-----+-------+------+ | Head | Milli-|Inch.|Feet.|Inches.| Lbs. | | in Feet.|meters.| | | | | +---------+-------+-----+-----+-------+------+ | 246 | 6 | ¹⁄₄ | 3 | 0 | 326 | | 311 | 7 | ... | 3 | 0 | 383 | | 360 | 8 | ... | 3 | 0 | 431 | | 393 | 9 | ... | 3 | 0 | 483 | | 426 | 10 | ... | 3 | 0 | 556 | | 476 | 12 | ... | 3 | 0 | 651 | | 590 | 16 | ⁵⁄₈ | 3 | 3¹⁄₃ | 977 | +---------+-------+-----+-----+-------+------+ This pipe is supported every 30 ft. on small masonry piers, on the top of which is placed a block of wood hollowed out to receive the pipe, thus allowing any movement due to the contraction and expansion of the conduit. However, to prevent this movement becoming excessive, the pipe is passed at intervals of 300 yds. to 500 yds. through a cubical block of masonry of 13 ft. side, strengthened by longitudinal tie-bars. Five bands of angle-bar riveted round the pipe, with their flanges embedded in the masonry, constitute a rigid fixed point. Straw mats are thrown over the pipe where it is exposed to the sun. The temperature of the conduit is not, however, found to vary greatly, since the pipe is kept full of water. To supply the rock-drills with water at a maximum pressure of 100 atmospheres, or 1470 lbs. per sq. in., a plant of four pairs of high-pressure pumps has been laid down, and a still larger addition is in course of erection. At present, two Pelton turbines of 250 H.P. each, running at 170 revolutions per minute, drive the pumps, by means of toothed gearing, at 63 revolutions per minute. These pumps are of very simple but strong construction, single suction and double delivery, entailing one suction and one delivery-valve, both heavy and both of small lift. The larger portion of the plunger has exactly double the cross-sectional area of the smaller portion, so that in the forward stroke half of the water taken in at the last admission is pumped into the high-pressure mains, and at the same time a fresh supply of water is sucked in. During the backward stroke half of this new supply is pumped into the mains, and the remainder enters the second chamber, to be pumped during the next forward stroke. Thus the work done in the two strokes is practically the same. The pumps are in pairs, and are set at an angle of 90°, to insure uniform pressure and uniform delivery in the mains. Their size varies; but at Iselle there are three pairs, with a stroke of 2 ft. 2¹⁄₂ ins., and the plungers of 2¹¹⁄₁₆ in. and 1⁷⁄₈ ins. (approximately) in diameter, supplying 1.32 gallons per second.