Page 158 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

140 Major Process Equipment Maintenance and Repair

6. The length of the distance bushing “K” (item 8) and ensure that its
ends are parallel within .03 mm (BO1 in.).
7. The distance from the inboard end of the sleeve to the first shaft
step outboard of the sleeve at the thrust bearing end of the rotor
“L.”
The clearances that will result from assembly can now be calculated,
and adjustments made:

Total End Clearance = (A + B + I + J) - (E + C + K + D + H)
Total Center Clearance = (K - F - G) - (I + J)

On a typical machine, these clearances should be .38 to .51 mm (.015
to .020 in.) per running surface pair. To adjust the center clearances it is
necessary to machine the center distance bushing (alter “K”). To adjust
the end clearances it is necessary to machine the impeller ends. If impel-
ler ends are damaged by a rub they must also be machined. If impeller
machining results in excess end clearances it will be necessary to ma-
chine the center bodies. The limit of impeller machining before center
body machining is necessary is typically .76 mm (.030 in.). When one
impeller is shortened it is also necessary to shorten the other impeller by
an amount equal to the amount taken off the first impeller multiplied by
the ratio of impeller lengths in order to maintain the original pressure
ratio.
When impellers and center bodies are shortened, the internal volume
of the machine, and hence capacity, is reduced. To restore the original
capacity it will be necessary to purchase and install new impellers and
center bodies.
The distance “Ey is critical to ensure that the entire assembly is located
at its correct axial position. Reassembly begins with the rotating element
and intermediate plates. Start by assembling the thrust end shaft sleeve to
the shaft with its locknut and washer, setting “L” to the original dimen-
sion. Stack up the rotor parts in order, including the intermediate plates
and finishing with the other sleeve locknut. This is most easily accom-
plished with the rotor standing on its thrust end. Check the clearance of
the intermediate plates to the impeller ends with feeler gauges. The body
can now be assembled, again beginning at the thrust end. Start with the
cover (item 2 in Figure 3-14). Use either O-rings or Permatex@ at the
body joints during this assembly. Insert the rotating assembly with the
intermediate plates when the first center body is installed. Finish this step
of the assembly with the other end cover and tie rods. With the body on
its feet, level the assembly and tighten the tie rods evenly to the recom-
mended torque values.