When you first got it, your centrifugal water pump was performing flawlessly. It sucked water and discharged it beautifully. But lately, you’ve noticed it is taking longer to prime. And once the pump is primed, it seems to discharge with less force and takes longer to drain the water. On the job site, this means more time, and time means it costs you more money. So, you want to know why your water pump is slowing down.

Key components for the water pump

The short answer, it is probably your impeller.

However, to minimize the wear in the future, and be sure you are using the right type of pump, you should know some things about the way the centrifugal pump works, and why the impeller is often the key offender in diminishing pumping power.

We have all experienced centrifugal force. It is what keeps us in our seats when we are on a looping roller coaster, or “pushes” us into the car door when the driver takes a turn at higher speeds. As you surmised, centrifugal pumps take advantage of that same force to push water through the pump housing.

The key piece of equipment at work in creating the centrifugal force is the impeller. The impeller is attached to the motor shaft inside the pump housing and spins at a high rate of speed. While the detail designs of various impellers differ, they all follow the same principle.

Impellers use vanes on their surface(typiclly), that “push” water away from the center point of the shaft. Since the impeller is generally in the center of the housing, the fluid is forced to the outer edge, which is where the discharge port is located.

The force or flow rate of the centrifugal pump is based on the design and dimensions of the impeller and the speed of the rotating shaft.

The problem with the impeller

When the impellers are new, they are the correct shape for the design of the pump. But that does not last. Over time, the constant flow of fluid over the impeller will wear down the material, changing the dimensions of the impeller. While this is true with all fluids (even clear water), it is particularly so with fluids that also contain suspended materials like sand, mud, sticks and other debris.

As the impeller blades are worn by the very process of pumping, their ability to pump is reduced. You will start to notice decreasing performance in priming time and flow through.

Fixing impeller problems

This one is easy. Replace it. You cannot actually repair impellers, but centrifugal pumps are designed so that you can replace the impellers. Since you may not have the luxury of waiting for replacement impellers to be shipped, it is a good idea to keep them on hand for when you need them. It doesn’t happen often, but when they wear down, it can cost you time and money, so having one on hand will reduce the time you spend with a low performing pump.

A couple more things.

If your impeller is wearing out more quickly than you think it should, talk to us. The problem may be that you are using a pump that was not designed for your needs. Just because “stuff” can make it through the pump doesn’t mean that the pump was designed to handle it.

Clogging is not the only issue caused by suspended solids in the fluid. Small solids, like sand, mud, and silt (abrasives) may not clog the pump as quickly, but their damage can be even worse. Excessive wear on the impeller may be an indication that the fluid has too many abrasives in it. This not only wears the impeller but can also damage the mechanical seal, which keeps the fluid from reaching the engine. If you are using the pump in a way that it was not designed to handle, the engine itself may be at risk.

If you have any questions about pump impellers or anything else about pumps and pump parts, give us a call at 1-800-PUMPBIZ (786-7249). We’re always happy to help.