Pump Wearing Ring Clearances
Typical clearance and tolerance standards for nongalling wearing-joint metals in general service pumps are shown in Figure 52. They apply to the following combinations: (1) bronze with a dissimilar bronze, (2) cast-iron with bronze, (3) steel with bronze, (4) Monel metal with bronze, and (5) cast-iron with cast iron. If the metals gall easily (like the chrome steels), the values given should be increased by 0.002 to 0.004 in.
The tolerance indicated is positive for the casing ring and negative for the impeller hub or impeller ring.
In a single-stage pump with a joint of nongalling components, the correct machining dimension for a casing-ring diameter of 9.000 in would be 9.000 plus 0.003 and minus 0.000 in. For the impeller hub or ring, the values would be 9.000 minus 0.018 (or 8.982) plus 0.000 and minus 0.003 in. Diametral clearances would be between 0.018 and 0.024 in. Obviously, clearances and tolerances are not translated into SI units by merely using conversion multipliers; they are rounded off as they are in the USCS system. The SI values for the previous USCS examples given are outlined here.
For a single-stage pump with a casing ring diameter of 230 millimeters, the machining dimensions would be as follows:
Casing ring 230 plus 0.08 and minus 0.00 mm
Impeller hub 230 minus 0.50 (229.5) plus 0.00 and minus 0.08 mm
Diametral clearances Between 0.50 and 0.66 mm
Naturally, the manufacturer’s recommendation for ring clearances and tolerances should be followed.