Pumps critical to delivering reliable water supply

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CAP Infographic Pumping Plant Anatomy

Water industry professionals refer to pumps all the time, and CAP is no different, except by scale. By its very definition, a pump is a device that raises, transfers, delivers or compresses fluids. They are everywhere in our everyday life, often humming along, unnoticed in pools, vehicles, air-conditioning systems, washing machines and more.

Within the CAP system, there are hundreds of pumps of all sizes, each performing very specific tasks, but the thing they have in common is that they are big.

The largest pumps are in the pumping plants. Their purpose is simple, but not easy: lift millions of gallons of Colorado River water from a lower elevation to a higher elevation so gravity will allow it to flow through the canal, carrying it across our state. And water is heavy – one gallon weighs more than eight pounds!

Of CAP’s 109 pumps, 79 have a design very similar to this infographic. Each is a centrifugal pump, the most common type used in water and wastewater plants. The shaft-driven impeller rotates inside an air-tight casing. The impeller is submerged in water and spins rapidly when the pump is operating, using centrifugal force to move the water. Centrifugal means the force is moving away from the center, or in this case, the impeller. These pumps are located near the bottom of the pumping plants, below the upstream canal water level to meet design requirements and ensure sufficient pressure exists at the impeller inlet.

There are some differences among CAP’s pumps, too. The amount of vertical lift for the pumps in each pumping plant varies widely, as does their size. At the beginning of the CAP system, Mark Wilmer Pumping Plant is the largest, designed with six pumps rated at 625 CFS (cubic feet per second) each that lift water more than 800 feet. Not surprisingly, each of the motors that drive these pumps are approximately 66,000 horsepower. Sandario Pumping Plant, the eleventh plant in the system near the terminus near Tucson lifts water just 75 feet; three of its pumps are rated at 155 CFS with 2,000 horsepower motors and three are rated at 50 CFS with 700 horsepower motors.

No matter the size or the amount of lift, each of these pumps are a critical component of the amazing infrastructure that ensures the reliable delivery of Arizona’s Colorado River water.