Patent ID: 7824237

Claim:
A water propulsion unit including an upstream impeller and a downstream impeller, a pump housing, a water inlet to communicate with the upstream impeller and an outlet to directly communicate with the downstream impeller, the said impellers being mounted on and, in use, driven by shafts so as to be co-axial with each other, within the pump housing; wherein said impellers are spaced apart and are adapted to be rotated within the pump housing in opposite directions, and wherein each impeller includes a series of impeller blades extending radially from a central boss, and the blades of the upstream impeller are of opposite pitch to the blades of the downstream impeller, wherein the water propulsion unit is designed to operate efficiently in the range of 0-40 psi; one of the impellers is arranged to impart less energy to the water than the other impeller; and the cross-sectional area of the outlet is such that in use it presents minimal impedance to the flow of water therethrough.