Can A Centrifugal Pump Run Backward?

One of the most common mistakes when operating a pump, believe it or not, is reverse rotation. This occurs if the pump uses reversible motors, which can run either forwards or backwards. In essence, the pump, which should operate clockwise, operates counterclockwise (or vice versa). In layman’s terms, it runs backward.

What are the risks of reverse rotation?

If your pump is wired improperly, you could be reducing flow by up to 70%. The impeller could jam or become unthreaded. If rotation is backwards, the impeller and acorn nut can spin off in just a few seconds, causing damage to the pump’s components such as the bearings or seals. This could completely destroy your centrifugal pump if undetected. Read more about pump maintenance and preventing damage and in our comprehensive guide.

So how does reverse rotation happen and how can I prevent it?

The shape of the impeller and design of the pump’s body can determine the path that liquid flows. If the impeller runs backwards, the liquid is still discharged from the pump. This is due to centrifugal forces that move the fluid in the normal direction. Put simply, the flow doesn’t reverse, making reverse rotation hard to detect. The risk of reverse rotation is higher when putting in a new pump system, or replacing parts. To be safe, it’s best to check which way the impeller rotates before you start pumping. If the pump is uncoupled, this can be done with a simple test, where you bump the power to your pump for a split second to check the direction of rotation. This is called a “bump test”.

Pumps that can rotate forwards or backwards will show the correct direction of rotation on the pump, usually seen on the casing, bearing frame or motor. Before doing the bump test, first check for rotation stickers showing which direction the pump should run. Secondly, connect the three wires to the motor. Now, check to see if the shaft turns clockwise when you bump the power. If it rotates counterclockwise, you’ll need to try something different. Switch two of the three wires. You can then try the test again.

This sounds really simple in theory. After all, what’s so difficult about switching a few leads? However, working with electrical wiring can be dangerous, both for you and your pump! Unless you really know what you’re doing, it might be safer to contact a qualified electrician.

If you’re unsure about how to check the rotation of your centrifugal pump, call our toll-free number at 1-800- 367-4180. We have experts on hand to help you choose, install, and maintain a variety of equipment.