Understanding Centrifugal Pump Cavitation
If you install a centrifugal pump incorrectly, it may still run and at first seem to be operating normally, however, a poorly engineered installation may cause centrifugal pump cavitation. At C&B Equipment we know all about centrifugal pump cavitation problems because we’ve helped many of our clients with them.
You want to be aware of the problem because it may cause expensive pumps to fail far sooner than expected. Here are some more details about this concern, what to watch out for, what to do if it is already happening, and what you can do to avoid this problem.
If you are having issues with your pump, please utilize the contact form here to reach out to our team!
An Explanation of Cavitation in Centrifugal Pumps
The scientific explanation for cavitation is a condition inside a centrifugal pump where the flowing liquid pressure drops below the vapor pressure. When this happens, little bubbles of vapor may form in the liquid.
These bubbles burst when they reach areas within the pump that are under higher pressure. Cavitation causes damage to the pump, making it wear out faster than it should, if it did not have this problem.
Some describe the sound of a pump experiencing cavitation issues as sounding like rattling marbles or gravel running through the pump. If you hear this weird rattling sound, and especially if your pump starts leaking, call C&B Equipment for maintenance service right away.
Types of Centrifugal Pump Cavitation
There are three types of cavitation. They are all bad, come from different problems, and you should try your best to avoid them. Here are the main cavitation types:
Suction – Your pump’s suction side pressure is too low.
Discharge – Your pump cannot expel fluid fast enough, so internal pressure rises.
Recirculation – Fluid circulates in your pump’s impeller instead of being expelled.
Pump Cavitation Causes
The top five most common causes of pump cavitation issues are the following:
- Blocked or restricted suction and/or discharge lines
- Low suction pressure
- Incorrect pump selection and/or improper installation
- Having a high fluid temperature
- Running your pump at excessive speed
There are so many improper installations that cause these problems. The pump may be the wrong size. It may be oversized for the suction side or discharge feed capacity or it may not be powerful enough to keep up with the desired flow rates.
Suction cavitation may be caused by using long, narrow pipes. Just having an unnecessary turn in your suction lines can cause blockage or restriction that reduces suction side or discharge pressure.
If the discharge flow rate is too low, that causes pressure to increase, and circulation problems add to this cavitation related to the discharge flows.
If you are running liquid at a high fluid temperature, it takes less flow restriction to cause vapor bubbles to form inside your pump. A similar thing happens when running your pump at excessive speed (too hot).
How To Prevent Pump Cavitation
Take all the potential problems we just identified above and do everything you can to reverse or eliminate them. For example, try to work with short, straight suction side or discharge piping.
Improving Your Pump Placement and Suction Side and Discharge Pipe Connections
Suppose your suction side is coming through a pipe that travels across your shop floor, runs up a wall, down and around another area and then feeds your pump. Under these circumstances, you will likely experience suction cavitation. To fix this problem may be as easy as moving the pump closer to the source and getting rid of turns in the discharge or suction side piping.
Consider lowering your fluid temperature if possible, and use the correct impeller size and type for the fluid dynamics you can measure.
Measuring Fluid Dynamics
You want to measure the Net Positive Suction Head (NPSH). The proper calibration is to have the NPSH available (NPSHa) greater than the pump’s requirements (NPSHr).
Avoid Excessive Speed
If you run your pump too hard and too fast, you are asking for trouble. We’ve seen cases where a solidly-made pump, which should last for years, was improperly installed and burned out in a few months.
We Have Seen It All
We had a new local client ask us to come for a site visit. It was a chance to show our expertise for a big upgrade. We could hear the old pumps in use when we walked in. Some were whining from running at such a high speed that every dog in the neighborhood could hear it. Others were rattling with obvious cavitation damage happening.
We made our recommendations, fine-tuned a new system design, and the new pumps were installed properly. At the end of the upgrade process, the factory had a much more enjoyable sound with all the pumps running exceptionally well and humming along as part of a well-oiled machine. Call us to learn more.
Cavitation Damage in Pumps
Cavitation causes pitting and erosion of the impeller and ruins other internal components. The damage begins to reduce flow and efficiency until it causes premature failure.
What happens if you ignore these issues? Usually, you already have a big problem when you first begin to hear that distinctive rattling sound. The worst case is catastrophic malfunction and ending up with a pump that is a very ridiculously large paperweight or can only be used as a doorstop.
That’s why our clients love to ask us to specify a job’s requirements for pumps— to review the proposed pump(s) in the plans, their location, the proposed connections, size, temperatures, and operational capacity.
If you make mistakes by not following the manufacturer’s installation recommendations, please don’t think your warranty will save you. Cavitation damage caused by improper installation and misuse is usually not covered by warranty.
Being a distributor of the most popular lines, not a manufacturer, gives us an advantage that allows us to make better recommendations, and we service what we sell, so we know a thing or two about what can go wrong and how to fix it.
Connect with us for help with centrifugal pumps and a whole lot more. We are a well-established “go-to” source in Wichita, Kansas, serving the community and surrounding areas.