Underwater pump

An underwater pump for excavating or sucking sands or gravel from the bottom of a sea or a river comprising a pump casing having a lower end, a motor water-tightly encased in said pump casing, an impeller casing integrally attached to the lower end of said pump casing, a cylindrical strainer disposed below said impeller casing and having a plurality of apertures formed on a wall thereof, a rotary shaft extending downwardly from said motor, a rotory head fixedly secured to the lower end of said rotary shaft, said rotary shaft extending through an inlet opening formed on a bottom plate of said impeller casing and a central opening of said cylindrical strainer,

• said rotary shaft including a rotary-head mounting portion disposed in a water flow path defined within said cylindrical strainer, and a stationary flexible-piece-winding preventing member encasing the rotary head mounting portion of said rotary shaft,
• said flexible-piece-winding preventing member being made of a circular sleeve having a diameter smaller than a diameter of said rotary head, said circular sleeve having a lower end thereof integrally connected with a circular rim portion of said bottom plate of said cylindrical strainer and an upper end thereof extending into said impeller casing through said inlet opening of said impeller casing wherein a circumferential gap is provided between said circular sleeve and said roatary head mounting portion.