Centrifugal pumps used in HVAC systems circulate water. We know this; it is their purpose, it’s what they do. Ever really think about how it does this?
Let’s start by pointing out the obvious – there is a motor. The motor uses electricity to rotate the shaft that rotates the pump impeller. The impeller, typically made of bronze or stainless steel, is shaped like a wheel. This wheel contains enclosed vanes that sling the water. (Imagine a tennis backhand swing.) So, an impeller slings water, while a propeller pushes water. (Imagine a boat motor.)
As the impeller spins, it creates a pressure differential between the center, or eye – where the water enters the impeller, and the outer edge of the wheel. That pressure differential is the force that moves the water. In other words, the pump is creating a low pressure point at its inlet and a high pressure point at its discharge. Water naturally moves from a state of high pressure to low pressure. In order for the highest pressure water at the pump discharge to get to the lowest pressure point at the pump suction, it MUST travel through the piping system. Hence, the water is circulated.
And those are the basics! Pop quiz later...
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