THE PRESSURE BOX.
The
pressure box is situated at the end of the ditch in a commanding
position above the claim, and from it the water is delivered into the
supply pipe. The box derives its name from the fact that the head or
pressure is measured from this point. Connected with or forming a part
of the pressure box is the sand box, which is sunk below the level of
the flume or ditch, and arranged to catch the gravel or sand carried
along by the current. It is emptied by a side gate as circumstances
may require.
The
pressure box is a large wooden receptacle, generally constructed of
i^-inch planks, and securely held together with timbers. It is
sufficiently large and deep to keep the head of the pipe, which enters
it, under water with a steady pressure.
A
grating of bars is arranged to catch all floating material, such as
sticks and leaves. The water should be quiet and sufficiently deep to
prevent any air from being carried into the pipe. For this purpose the
box is divided into compartments, one of which receives the water and
* See " Trans, of the Am. Society of Civil Engineers," vol. xii. No. 204, pp. 120-123.
