Pumping grit isn't that hard

January 5, 2018

We apply Gorman-Rupp pumps to a lot of applications pumping grit -- directly out of grit traps, as well as in other similar high-solids applications. The Super T and Ultra V Series pumps are fantastic for this kind of application, because they can work on a suction lift or on a flooded suction, and they are exceptionally easy to maintain.

There's no application quite like a headworks pumping installation to put a pump through the worst of its solids-handling paces, so the ease of accessing the impeller directly through the removable cover plate on a Gorman-Rupp self-priming pump makes a world of difference in reducing downtime and keeping the pump in service. Other pumps can only be serviced by moving the piping leading into the pump, and that's no way to operate a modern facility.

One of the recurring questions we encounter in grit service is what kind of material to use for the wetted parts inside the pump. Pumping grit is a lot like subjecting it to a constant sandblast. The default assumption in many engineers' minds is that the harder the parts, the better.

Don't make that assumption.

Hardening the parts does help to resist wear -- up to a point. But beyond a certain degree of hardness, metals tend to become brittle. For comparison, think of ceramics -- they're often extremely hard, but they also tend to shatter. You wouldn't want to get hit in the head with a ceramic vase, but you don't want to drop that vase on the floor, either.

The right metals for grit service are those that reach the optimal balance between hardness and strength. We have found Gorman-Rupp's specially-hardened ductile iron to be the best fit for the vast majority of municipal grit applications. It measures well on the Brinell hardness scale, but it also delivers much higher tensile and yield strengths than other materials that are very hard but also brittle.

In certain extreme-wear applications, Gorman-Rupp can deliver entire pump casings in this treated ductile iron, ensuring extraordinary service life in the toughest situations.

For those who are so inclined, we can offer a deep dive into the details comparing the different grades of metal available. But for most people the lesson is this: Hardness is valuable, but only up to a point. Be sure the metals you put into service have the right tensile and yield strengths -- you don't want to sacrifice strength just for the sake of going overboard for hardness.

If you have the appetite for more detail, don't hesitate to ask us!