quietly
discharges it into the second through lateral openings. There should
be no perceptible difference between the water-supply and the
discharge, or, if any, the former should be in excess, and the surplus
should be regulated and discharged by a waste-gate placed near the end
of the flume. Some pressure boxes are arranged for two pipes.
La Grange Pressure Box.—The following is a description of a pressure box at the La Grange Mine, Stanislaus County:
Some
350 feet to the rear of the pressure box there is a sand box in the
ditch connecting with the waste-way. This sand box is 2 feet deep
(below the bottom of the ditch), 4 feet wide, and 4 feet 3 inches long,
and communicates with the waste-way by means of a gate which slides
clear to the bottom of the box. At the pressure box the four end posts
and the two caps belonging to them are made of 6"x8" lumber. The six
intermediate posts, three on a side, are of 6"x6" material, and their
caps are of the same dimensions. All the sills, and the two
longitudinal stringers on which they rest, are of 6"x8" " stuff." Up to
high-water mark the box has a double lining made of two 1-1/2-inch
planks battened at the joints with strips 1/2 inch by 4 inches.
A 22-inch pipe takes the water. Nine feet from the box there is a
5-inch diameter stand pipe which extends 2 feet above the top of the
pressure box.
In
large claims the pressure box ranges from 10 to 20 feet in length with
a single pipe; and, where two pipes are used, from 12 to 30 feet.
Larger boxes are also built where the pressure, sand, and measuring
boxes are combined in one.
The
pressure box at the Bloomfield Mine is 18 feet long and 6 feet wide, so
arranged that the sand falls under a wooden diaphragm into a large
chamber provided with a gate.
