How to Kill a Centrifugal Pump | Great Lakes Pump

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How to Kill a Centrifugal Pump

Of course this is something nobody wants to do, tries to do. But it happens. And no doubt many people have troubleshot a failing system, come up with an idea, and then think to themselves, “I wonder what this would do to the pump?”

We’ve seen a lot and thought you might benefit from an understanding what actions will lead to pump fatality. This list is by no means comprehensive. By no means are we trying to poke fun at stupidity. Manufacturing is complicated. Equipment modules can't address every fault situation. Sometimes trial and error is necessary. We are simply ascribing to the idea that it is better to share probable outcomes of various trails than to have them blindly pursued.

Action What happens…
Completely neglect the instructions, operation, and maintenance manual (IOM), especially the part where it advises on proper pump and motor bearing lubrication. Over time not greasing the bearings, over-greasing them, or using incompatible grease will cause the bearings to seize and the pump to stop rotating.
Deadhead the pump for an extended period. Deadheading means you shut off the pump’s ability to discharge fluid by closing a valve. The fluid will churn inside the pump until it heats into a vapor. Once a vapor, any bushings or mechanical seals in the pump can heat to the point that they can either crack, shatter, score, compromise elastomers…and ultimately kill the pump.
Run the pump dry for an extended period. There are exceptions to what occurs by starving the suction of the pump, but it is a killer (and is also one reason why air operated diaphragm pumps came to be). You’ll produce the same result as deadheading the pump, and now you’ve also introduced a state of cavitation. The pump’s impeller is now receiving little to no fluid, usually causing irreparable damage.
Introduce pipe strain through inlet and/or discharge piping that causes side loading to the pump and therefore constant stress to the housing, shaft, bushings, and pipe connections. Sometimes you can get away with a not so perfect installation. Maybe the pump will give you “several” years of trouble-free operations instead of “many, many” years. We’ve also seen cases where failure occurred within months, where pipe strain is easily identified as the culprit. Click here for guidelines on avoiding pipe strain
Connect a motor that is incompatible with the electrical service being supplied to the plant. Electrical service in the USA is 60 Hz. In many other countries it is 50 Hz. In the USA 208 to 480 voltage is standard with motors engineered for 3 phase current. In Canada, their electrical grid supplies 575 volts. In other parts of the world both Hz and voltage vary. While some motor manufacturers are building motors compatible in both 50 and 60 Hz environments, wiring the motor for the actual Hz is required.
Connect a 50 Hz motor to 60 Hz service and the motor will slowly burn out. Connect a 460-480v motor to 575v service and it will quickly trip the breaker or amp fuses. Connect a 460v motor where 380v is supplied and the motor will be starved for power, creating a low torque situation. It will be weak for sure and then slowly overheat and die.
Misalign the motor and pump shafts Sometimes misalignment will only cause the coupling to fail and render the pump temporarily out of service. However, in some instances the coupling will tolerate the mis-alignment long enough to sufficiently stress the pump’s power frame bearings and mechancial seal, causing pump failure.
Undersize the motor for your application The more gallons a pump is producing, the greater the workload on the motor. Properly sized motors will not be too taxed in the event there is maximum workload (GPM is maximized due to minimal discharge backpressure). Perhaps throttling devices have not been installed, or too many or too large nozzles are installed. When this happens a pump can “run off its curve” and overload the motor. Because there is risk of this event automotive manufacturers specify that all pump motor selections must be non-overloading (NOL). This is relatively cheap insurance to protect against human error.
Install an iron pump when stainless steel is required for handling your fluid It is simple. Fluids that will corrode iron will cause the pump to fail.
Poison your pump Nobody does this deliberately, but in complex manufacturing environments it happens more than anyone cares to remember. Tank cleaning can require use of acids that can swiftly destroy elastomers in mechanical seals, valves, heat exchanger equipment if introduced at too high a concentration. In another horrible episode, cleaning fluids were not completely flushed from tanks before re-introducing paint, causing the combination to coagulate and foul the entire system.
Select a low-cost, basic mechanical seal designed for pumping clean water when you truly need a beefed-up seal. In one recent example, a low-cost carbon and ceramic faced seal with Buna elastomers was used for a limestone cutting operation with a reclaimed water system. Both a pressure and gravity filter were installed, but the fine particulate in the water caused the seal to fail and the fluid to reach the motor, causing it to fail as well. Please use caution when selecting seals.
Allow work rags, gloves, and other debris to get into your pump well Like vortex, chopper, or some other similar design, the introduction of an impossible-to-pass solid will lock up your pump. What happens next can vary, but let’s say your pump ingested a thin rag. Your impeller(s) shredded and passed some of it before the bulk of it caused the pump to lock up. Immediately, your pump motor amps skyrocket, blowing a breaker or fuses. You may have fried your motor too. In addition, those little rag pieces moved through your system until the pump locked up. If your application is a trash pump disposing of solids-filled effluent, all is good. But if you have nozzles post discharge, those rag fibers will clog your nozzles once that pump get repaired and is fired up again. The double whammy.

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