Pumps FAQ

Pump FAQ

Answers To Your Most Pressing Pump Questions

Below are some of the most common questions we receive from our customers regarding pumps. The answers are provided by our knowledgeable pump specialists, and they may help you solve some of the challenges you’re experiencing. Need more answers? Simply contact one of our technical experts today.

Q: My pump sounds like it is pumping gravel. What is causing that noise?

A: It is likely cavitation. Cavitation means that cavities or bubbles are forming in the liquid being pumped. Symptoms of cavitation include excessive noise and vibration and loss of capacity, pressure and efficiency. Cavitation can cause damage to the pump. Solutions include changing the operational parameters or even replacing your pump with a pump better suited to the application.

Q: If I put a bigger motor on my pump, will it pump more?

A: No. The amount of water and the pressure (head) that a centrifugal pump produces is related to the rotational speed, impeller diameter and size of the impeller vanes.

Q: If I put a higher speed motor on my centrifugal pump, will it pump more?

A: It will pump more, but it will likely overload the motor. If you double the rotational speed of the motor from 1800 RPM to 3600 RPM, the horsepower required by a centrifugal pump actually increases by a factor of eight. Increasing the pump speed may also pressurize the pump beyond a safe working pressure and overload the shaft and bearings. Increasing the impeller is another option. Your OTP pump expert can review your application and make appropriate recommendations.

Q: My pump starts and stops a lot. Will this hurt the motor?

A: It might. Every time the motor starts, the windings see a high inrush current of up to about 10 times the nameplate amps (locked rotor code M). The motor dissipates the inrush of energy as heat. If you start the motor too many times, a build up of heat can cause damage to the motor.

Q: My pipeline shakes and sounds like a sledgehammer striking the pipe when the pump starts and stops. What’s that noise?

A: What you’re describing is likely what is referred to as “water hammer” and it has to do with the changing velocity of the water inside the pipeline.

Picture a game of baseball. The pitcher has thrown the ball. There is no sound until the ball hits the bat or the catcher’s mitt. Fast moving water in your pipeline is like the baseball—it makes little noise until it accelerates quickly or stops quickly (water hammer).

When the moving water accelerates or stops, it applies a force to whatever it happens to hit. In your pipeline, if the high velocity water hammer hits a pipe fitting hard enough, it can actually burst the pipe.

Q: Can I put a mechanical seal on my packed centrifugal pump?

A: Probably. There must be enough physical room to install one. Sometimes you may need to have some machine work done to “true up” surfaces that have corroded over time or that were never machined originally because the pump was designed to be packed.

Q: Why won’t my pump prime?

A: The pump is likely not being fed properly or there could also be Net Positive Suction Head (NPSH) issue related to the temperature or type of fluid. Unless the pump you have is a “self priming” pump, it will not prime unless the pump is full of water and there is no air trapped inside locking the pump.

Q: Why do I keep “burning” up my mechanical seal?

A: If the mechanical seal is being used in a hot water application, the water may be turning to steam and evaporating (flashing off), which leaves the seal faces with no lubricant. Either change to a special mechanical seal designed for hot water applications or install a cooling water plan to prevent flashing.

The problem could also relate to materials incompatibility, improper installation, running dry due to lack of water or the systems application. I suggest you contact an OTP mechanical seal expert to discuss the details.

Q: Will a centrifugal pump really work if it is running “backwards?”

A: Somewhat. If the motor and pump are running backwards, the pump can often still move water, and the water will flow the normal direction through the pump.

A centrifugal pump accelerates water off of the tips of the impeller vanes. When an impeller is running backward, the centrifugal forces will still accelerate the water—although far less efficiently. A backward running pump will deliver less water, at a lower pressure, and will typically consume less electricity. If the impeller is threaded to the shaft, it may unscrew when running backwards.