Wear rings can be defined as a device used to seal the pressure leakage of the liquid between the inlet of the impeller and the pump casing. Clearances at the wearing rings should be within the limits recommended by the manufacturer. Excessive clearance reduces discharge and efficiency of the pump. If the wear is only on one side, it is indicative of misalignment. The misalignment should be set right, and the causes of misalignment should be investigated. When the clearances have to be restored. Normally, if the clearance in wearing rings increases by about 100% for small pumps and 50-75% for large pumps the rings shall be renewed or replaced to restore to the original clearance.
The typical reason for using a wear ring is to decrease the amount of leakage loss around the impeller. Due to more work available to push the pumped liquid out the discharge there is a slight improvement in pump efficiency.
If inside of wearing ring is 125mm then diametral clearance should be up to 0.35mm. The tolerances of wear rings are to be strictly followed. For example, while machining the internal diameter of the casing wearing ring of basic size, say 125 mm, the limits for machining would be 125.00 minimum and 125.05 maximum.
Wear ring clearances are very similar to impeller clearances, but you lose 1% pump capacity for each 0,025 mm of wear. A typical clearance would be 0.0025 inch/inch diameter with 0.010 inches (0.25 mm) minimum clearance for wear rings less than 50 mm in outside diameter.
A common problem with wear rings is their ability to lock up or wear out which causes maintenance headaches. Due to the design of most closed impellers and wear rings, particulate tends to build up between the impeller shroud and the volute.
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