To control the contracting flow occurred in the vicinity of a drop shaft outlet of the inside of an outflow pipe to prevent a water current flowing through the outflow pipe from speeding up and, at the same time, to reduce variations in water pressure to stabilize the velocity of a turning current flowing down the inside of a drop shaft 1 or a flowing state.
An outflow pipe 6 supplying water 3 flowing out from an outlet 5 of a drop shaft 1 to a storage pipe 7 is connected to the lower part of the drop shaft 1 mounting an upper spiral plate 9 and a lower spiral plate 11 to the inside thereof in the direction of the circumferential tangent of the drop shaft 1. Then, a conical cone 27 is mounted on the bottom plate 2 of the inside of the drop shaft 1.
NAKANISHI TOSHIO
KAWASAKI SATOSHI
