Submersible pumps

Claim 1

Apparatus for controlling the operation of a cellar drainage pump, including (a) piezo-electric level detecting means which comprises a circular cylindrical plastic housing having a recess and a cavity, also of circularly cylindrical configuration, a membrane arranged in said recess to close said cavity, with a first face of said membrane serving to sense a fluid level and thereby derive an electrical signal, a piezo-electric body with such circularly cylindrical configuration mounted on said membrane with said piezo-electric body being mounted on a second face of said membrane inside said cavity and capable of translational oscillation along an axis lying substantially perpendicular to said membrane, (b) control circuitry means, including a first electrical conductor connected to said control circuitry means and to one end of said piezo-electric body, and a second electrical conductor connected to said control circuitry means and to the other end of said piezo-electric body by way of said membrane, and (c) switching means for said pump so as to enable said piezo-electric level detecting means to sense by acoustic impedance transitions, the presence or absence of liquid adjacent to said detecting means; said detecting means being electrically connected to said control circuitry means; said control circuitry means being electrically connected to said switching means for controlling said switching means, and said detecting means being mounted in a recess on the outer casing of said pump.