Why is your centrifugal pump operating with excessive power? In this edition of the Centrifugal Pump Minute, James Farley, Senior Director of Product Management for Griswold, reviews the likely causes for excessive power and provides remedies to troubleshoot the issue.

We also have an opportunity for a pump to operate with excessive power. In this case, the pump is operating, but it’s pulling for drawing more power than expected. This would typically be found where the pump is pulling so much power that it’s tripping some sort of an overload either on a VFD or on a control panel where the motor is overloading. You might be able to if you’re monitoring your power consumption closely you can catch it before it throws that kind of an alarm or error.

There’s a variety of issues that could cause excessive power for a pump and the first one would be that the system may have a lower head than it was designed for and so this goes back to basic centrifugal pump hydraulic performance. If the system power is lower than expected through the design the pump may be operating further to the right of a hydraulic performance curve where it’s providing higher flow rates because the head of the system is lower than expected and if this is happening the pump is operating further to the right of the curve and this is typically going to cause the pump to draw more power. You’re also getting more flow out of that pump where you should be if this is the condition and you may catch that because your system flow rate is higher than the rated flow rate.

There are a few things that you can do to help correct this issue. The most basic although not necessarily ideal would be to throttle the discharge of the system with some sort of a throttling valve and that will create a false head in the system that will take the pump and make it operate closer to the rated low and head and you should see a reduction in power consumption in this particular case. Maybe a potentially better solution than just falsely throttling the discharge to create a false head would be to trim your impeller so that the pump is the impeller trim is properly sized to the actual head of the system. So you could do an impeller trim adjustment the dial and the performance of the pump and this should also help you run at a lower power.

Another option would be to install a VFD and then control your pump and the system performance directly through speed control and rpm control. Other aspects could be that the liquid is heavier than expected so if your specific gravity or your fluid is high then the power draw is going to be higher than expected. In some cases, people just generically use the specific gravity of water when sizing a motor for a system and this will this could cause the power, in reality, to be higher than expected because a higher specific gravity fluid is going to consume more power at the same rated condition. This could be a review and potentially there’s a need to increase the motor power just because of the specific gravity and then you can get into if it’s a packed pump if your packing is too tight on the shaft that can contribute to a lot of additional power consumption. Adjusting your packing could be one of the things that you need to check and then additionally you might have some sort of a rotating element that is contacting. It could be an impeller, it could be other aspects as well.

Watch the previous Centrifugal Pump Minute!