# Centrifugal Pumps: How Do They Work?

RL Deppmann
/
January 8, 2024

How a centrifugal pump moves water may seem too basic for engineers and contractors to spend time reading about. However, understanding how a centrifugal pump works will help in proper selection and application as well as proper service and troubleshooting. We begin this series by examining how a centrifugal pump operates and the basic parts of these pumps.

## Positive Displacement Pumps

A good way to begin the article is to talk about a different type of pump, the positive displacement pump. We do this because this is how most people think all pumps work. Most of us have used the pump shown above. If we have not used it, we have become a victim of it thanks to a brave 10-year-old.

We load the marshmallows into the “pump” and create pressure. When that pressure is released, the projectile is pumped out. Look out! Ouch!

A positive displacement pump works in a comparable manner. Our pump is grabbing a slug of water and some sort of pressure pushes the water out and into the pipe. If you block the outlet, the pressure builds. You may even break the pump if it continues to build pressure with a closed discharge.

Another type of positive displacement pump many have used. A centrifugal pump works in a much different way.

## Centrifugal Force: A Simple Example

Well, if we are using a marshmallow gun for one pump, let’s use another fun thing for centrifugal pumps.

This ride shown above or a “round up” rise or graviton type ride all work on centrifugal force. On this ride, no one is pushing on the people to pin them to the fence. Centrifugal force is the action they are experiencing. The faster it turns, the more force the person experiences.

What would happen if the ride were going and somehow a person dropped into the center of the ride? Centrifugal force would push them to the fence again.

Imagine: what if the fence behind them broke? Centrifugal force would cause them to fly out of the ride.

If a person flew out of the ride and into a pipe that then flowed into the middle of the ride, centrifugal force would send them out again. If this person did this once a minute and their name was George, we would have a flow of 1 GPM or George per minute. (SOOOO SORRY 😊)

## Centrifugal Pump Impellers

Now let’s look at centrifugal pumps. We will use a couple of figures from a Xylem, Bell & Gossett technical manual TEH-1166B

Here is a closed centrifugal pump impeller. Water is available at the inlet or eye of the impeller. The impeller is turning. The water moves from the eye to the outlet through vanes. It is important to note that the vanes are “slapping” the water, not digging into the water. Nothing is grabbing the water and physically pushing it. Centrifugal force is at work.