Abstract: A rotary pump having a plurality of rotor structures disposed in a pump casing, each structure having a rotor disposed in a casing, a hollow drive shaft each for driving said rotor, a headed bolt disposed within the hollow drive shaft for attaching said rotor to the drive shaft, an internally threaded rotor shaft being attached to the rotor and having said bolt threaded therein, the rotor shaft being disposed within an enlarged diameter hollow end of the hollow drive shaft, and the head of the bolt is disposed at the end of the hollow drive shaft opposite to its end to which the rotor is attached, whereby no rotor attaching means are employed on the face of the rotor opposite to the rotor shaft, and the pump casing has a flat rotor cover over the rotor structures, without any substantial spaces between the rotor cover and the rotors.

Abstract: This invention relates to a water soluble agent including a water soluble glass containing monovalent silver ions in its glass component. In water or an aqueous solution, the water soluble glass of the invention is capable of releasing the monovalent silver ions as required in an effective amount over a long period, the monovalent silver ions excelling, for example, in eliminating or preventing the occurrence of aquatic bacteria or other aquatic life forms, sterilizing them, preventing the occurrence of algae, and preventing water contamination.