Hale SMR - Manual (Page 68)

Preventive Maintenance
4-16 Stainless Max Series Pumps
5. If the apparatus does not reach performance levels, refer to
Section 5, “Troubleshooting” in this manual.
6. Compare the results of this test to those from when the
apparatus was delivered. The apparatus may not have
shown the 10% reserve at delivery.
7. If the apparatus performance has dropped appreciably com-
pared to its original performance, it needs to be serviced.
Note: Apparatus test results should be on file with the delivery
documents. If not, they may be obtained from the apparatus
manufacturer or from the original certifying authority.
Worn Clearance Rings and Impeller Hubs
Before assuming that clearance ring wear is at fault or that clear-
ance ring replacement requires pump disassembly, it is advisable to
thoroughly check other possible causes of low performance.
Clearance rings limit the internal bypass of water from the discharge
side of the pump back to the suction. The radial clearance between
the impeller hub and the clearance rings is only a few thousandths
of an inch when new. In clear water, the clearance rings continue to
effectively seal for hundreds of hours of operation. In dirty or sandy
water, the impeller hub and clearance rings will wear faster. The
more wear, the greater the bypass and lower pump performance.
When new, the radial clearance between the impeller hubs and the
clearance ring is between 0.005” to 0.007” (0.0127 to 0.0178 mm)
per side. Any increase will allow more bypass and result in lower
performance.
Clearance Ring Measurement Impeller Measurement
Figure 4-11: Clearance Ring and Impeller Measurement