Page 154 - Improving Machinery Reliability

126 Improving Machinery Reliability

Axial position of impellers relative to guide vanes needs to be reviewed in
conjunction with rotor float dimension. Is rubbing likely to occur?
List of connections may uncover dimensional mismatching with purchaser’s
lines, excessive flow velocities, omission of specified injection points, etc.
2. Cross-sectional drawing and bill of materials
These documents are primarily used for verification of impeller dimensions
and internal porting, visualization of maintenance access, materials selection,
and assessment of number of spare parts needed, etc. A copy of this drawing
and the bill of materials should also be forwarded to responsible maintenance
personnel.
3. Rotor assembly drawing, including:
a. Axial position from active thrust-collar face to:
1. Each impeller
2. Each radial probe
3. Each journal-bearing centerline
4. High-pressure side of balance drum
b. Thrust-collar assembly details, including:
I. Collar-shaft fit with tolerance
2. Concentricity (or run-out) tolerance
3, Required torque for locknut
4. Surface-finish requirements for collar faces
5. Preheat method and temperature requirements for “shrunk-on” collar
installation
c. Balance drum details, including:
1. Length of drum
2. Diameter of drum
3. Labyrinth details
d. Dimensioned shaft end(s) for coupling mounting(s)
e. Bill of materials
Axial position data are required for rotor dynamics analyses and maintenance
records. Accurate rotor dynamics studies would further require submitting
weight or mass moment of inertia data for impellers and balance drum.
Thrust-collar assembly details are to be analyzed for non-fretting engagement
and field maintenance feasibility. Hydraulic fit is preferred.
Balance-drum details are needed for rotor dynamics analyses and mainte-
nance reviews.
Dimensioned shaft ends for coupling mountings allow calculation of stress
levels, margins of safety, uprateability, and coupling maintenance.
The bill of materials is used to compare component designs and materials
being released for fabrication. Again, the bill of materials will allow definition
of spare parts requirements.
4. Thrust-bearing assembly drawing and bill of materials
These are used to verify thrust-bearing size and capacity. They are important
if directed oil-spray lubrication has been specified, and are essential mainte-
nance information.