Page 483 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

460 Major Process Equipment Maintenance and Repair

flgure 9-8. Typical pulse type fitter (Reference 9).

installed to extend the life of the more costly high efficiency media. In
recent years the development of the automatic self-cleaning filter (Figure
9-8) has greatly decreased the complexity of standard filtration systems
and reduced the amount of maintenance required. They are designed for
an element life of approximately two years at a fairly constant pressure
drop of two to three inches of water column. Self-cleaning filters are es-
pecially attractive in cold climates where other filter types would require
costly preheat systems for anti-icing.
Mechanically, axial compressors require very little routine mainte-
nance. Problems normally encountered include tip rubs, sealing strip
rubs, and foreign object damage (FOD). In the design of the axial, ex-
treme care must be taken to avoid blade resonances; however, these prob-
lems are rare in the field on equipment other than prototype machines.
Figure 9-9 illustrates the axial compressor rotor from a two-shaft indus-
trial gas turbine in the balance stand. With all of the inlet precautions
described it would seem unlikely that FOD would occur, but sometimes it
does. Often when a shallow nick is discovered in the upper portion of the
blade, it may be left “as-is” or “blended,” that is ground to minimize the
stress concentration factor. If it is too deep or too low on the blade pro-
file, blade replacement may be necessary. This can be either very easy or
very difficult depending on the design of the specific axial compressor.