Importance

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Abstract

A centrifugal pump for a fluid tank includes a pump housing enclosing an electric motor, a primary impeller coupled to the drive shaft of the motor, and a secondary impeller extending axially downward from the primary impeller proximate to the floor of the tank. The secondary impeller has a central stem and helical blades formed integrally with the stem and extending radially outward therefrom. An outer shroud encloses the central stem and helical blades of the secondary impeller. The outer shroud is fixedly secured to the helical blades and rotates in conjunction with the secondary impeller. The secondary impeller is either formed in one piece with the primary impeller or is removably attached by, e.g., screwing a threaded shaft on the secondary impeller into a corresponding through-bore in the primary impeller and the motor drive shaft. The secondary impeller has a smaller diameter than the primary impeller such that the primary impeller has a first fluid flow path directly from the fuel tank and a second fluid flow path through the secondary impeller. When the level of fluid in the tank is above the level of the primary impeller, the primary impeller draws fluid directly from the tank into the pump. The secondary impeller also provides a small amount of fluid to the primary impeller, and the primary impeller operates at or near its maximum possible capacity. When the level of fluid falls below the working level of the primary impeller, the primary impeller ceases to draw fluid directly from the tank, however, the secondary impeller continues to draw fluid up to the primary impeller to maintain operation of the pump. The secondary impeller thereby draws fluid down to a lower level in the tank to maximize the amount of usable fuel in the tank.

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First Claim