The advent of centrifugal pumps for aquarists was one of the most important advances for our hobby. Even fans of modern protein skimmers might admit that their skimmer would not work without its  pump. Arguments aside, centrifugal pumps are often the heart of any reef aquarium. This article was written to provide a basic understanding of the principles of centrifugal pumps and the construction of two popular types.
Centrifugal force is the phenomenon that exerts an outward force on matter that is being rotated. It is proportional to the radius of the orbit and the rotational speed squared. This principle and the proportions are what govern the design considerations of the centrifugal pumps we use. The pressure developed at the outside radius of a pump is proportional to centrifugal force.
Aside from the motor, a centrifugal pump generally has two major parts:
The rotating portion of the pump is called the impeller; it is mounted on a shaft and commonly has several radial fins or blades to apply force to the water as the impeller rotates.
The stationary portion of the pump is called the casing. The casing acts as a housing for the impeller, provides a path of water to the center of the impeller and contains the pressure developed by the impeller and channels the water to the discharge port of the pump. The casing also commonly provides supports for the bearings for the impeller shaft.
The terminology of pump characteristics:
Head is a measure of pressure, usually expressed in feet of water column. One foot of head is the pressure felt at a depth of one foot of fresh water. 1 pound per square inch (PSI) equals 2.3 feet of head.
Shutoff head is the pressure at which a pump cannot cause water to flow. If a discharge gage were installed, this pressure could be identified when the pump discharge valve was closed.
Suction head is the term used to describe the height of the column of water over the suction of the pump.
Flow rate, as we all know, is the measure of mass or volume moved over an amount of time. For our purposes gallons per hour (GPH) is most commonly used.

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2012-08-28

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