A submersible pump adapted to pump out the liquid in a reservoir has a built-in control unit for alternate pump operation. The control unit includes step memory means which provides a signal to permit the starting of pump operation every other time a high liquid level sensor senses the liquid. Once started,...http://www.google.com/patents/US4437811?utm_source=gb-gplus-sharePatent US4437811 - Submersible pump with alternate pump operation control means
