The Covington 12 inch, 18 inch, and 24 inch grinders with a center water feed attachment have a sleeve on the shaft that provides water up through the shaft for accessories like our diamond cones and domes. When you are using just the external water supply on these grinders, you need to remember to also turn on the water for the center water feed as well.
The grinders come with two brass center plugs. One has a hole in the middle for when you want to use the center water feed and one is a solid brass plug. When you are using the external water supply and not the center water feed, put the solid plug into the center of the grinder and be sure to turn on the water for the center water feed as well.
This keeps the bearings on the water sleeve cool and prevents them from overheating. The sleeve has a release valve on it so any water directed to the center water feed while using the solid brass plug will drain into the drain line system, but it will allow the water sleeve to stay cool and not burn out your bearings.
If you hear a knocking sounds while your grinder is running, you have burnt out the bearings on your water sleeve and it may need to be replaced.
Please contact us for details on getting your water sleeve replaced.