American Stainless Pumps, Inc.
www.aspumps.com
6
Setting Impeller Clearance
:
Model SSP Only
See SSP Performance Notes for impeller shimming discussion
www.aspumps.com/products/ssp/3500-
rpm/ssp_perf_notes.htm
Properly setting the impeller to case clearance is the most critical factor in determining the SSP’s
performance.
You will get maximum performance and efficiency (and maximum amp draw) with near to zero clearance. Factory
standard clearance is 8 to 12 mil. Spacer/Washers to adjust clearances are available in 10 mil and 15-mil thickness,
and can be ordered as a kit from the factory, p/n 720101.
You can have more or less than normal flow and head by changing the clearance. To increase clearance, remove
impeller spacer/washers. To decrease clearance, add impeller spacer/washers.
Be aware that if you set the
impeller at near to zero clearance, and operate near maximum flow rates, you may overload the standard
motor. Also be aware that impeller clearances near zero greatly increase the risk of the impeller grinding
against the casing.
Standard factory settings for spacers are 30 to 90 mils of spacer/washers to obtain 10-mil clearance. Since the
tolerances of the motor shaft and pump parts can stack up, some pumps may need more or less than this standard.
Some special OEM assemblies will not have any spacers when the customer elects to accept reduced performance in
return for ease of assembly.
Use the following impeller shimming method when building a new pump
1. Place the pump (as assembled through step 4 of the Assembly section above) on the workbench, positioned
vertically.
2. Place 0.050” shims onto the motor shaft (two 0.015” shims and two 0.010” shims).
3. Thread the impeller onto the shaft, compressing the seal and shims. You will need to hold the motor shaft from the
rear of the motor with a large screwdriver, wrench or vise grips while tightening the impeller.
Wear leather gloves to
avoid cuts when holding impeller while tightening.
4. Place casing (item 100) onto seal plate
without
casing o-ring (item 500). Install 4 case screws (item 7CS) and tighten
moderately (20-30 inch pounds torque). This is a time saving step to allow for observation of impeller clearance. Try
to view through the suction and discharge nozzles, the impellers clearance between the vanes and casing. Rotate the
shaft while listening and feeling for contact between the impeller and casing. Alternatively, use a feeler gauge to
measure the clearance between impeller vanes and pump casing. This can be done through either the suction nozzle
or the discharge nozzle.
5. Add or remove shims/washers from behind the impeller to achieve proper impeller clearance, and repeat step 4.
When proper clearance has been established, remove the 4 casing screws and the casing, and proceed to
step 9 in
the Assembly Instructions above.
