This invention relates generally to a high volume, buoyancy controlled submersible pump assembly designed to sit on the bottom of a body of water or other liquid substance and move a large volume of water or liquid substance. Alternatively, the submersible pump assembly is capable of achieving and maintaining neutral buoyancy or near neutral buoyancy in a particular body of water or liquid substance. The neutrally buoyant version includes maintaining the pump assembly at a given depth without requiring it to sit on the bottom of the body of water or other liquid substance. This invention also relates to linear electrofusion for thermoplastic components.