What is the function of a 'wear ring' in a centrifugal pump?

The function of a wear ring in a centrifugal pump is to provide a replaceable running clearance between the rotating impeller and the stationary pump casing or impeller housing. Centrifugal pumps rely on close clearances between the impeller and the casing to minimize leakage from the high-pressure discharge side back to the low-pressure suction side. This leakage, known as recirculation, reduces the pump's efficiency. Instead of machining the impeller and casing to very tight tolerances, which would be expensive and difficult to maintain, wear rings are used. These are separate rings made of a material that is resistant to wear and corrosion, and they are fitted into the casing and/or onto the impeller. The wear rings have a close running clearance, typically a few thousandths of an inch. As the pump operates, small particles in the fluid can cause erosion and wear of these surfaces. Because the wear rings are replaceable, they can be easily replaced when the clearance becomes excessive, restoring the pump's efficiency without having to replace the more expensive impeller or casing. This significantly reduces maintenance costs and downtime. Wear rings are typically made of materials like bronze, stainless steel, or specialized alloys designed to provide good wear resistance and compatibility with the pumped fluid.