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Process Parameters 229
thrusting caused by variations in the discharge pressure required by the downstream
system.
Mechanical Failures
Because of the extremely close clearances that must exist within the blower, the poten-
tial for serious mechanical damage or catastrophic failure is higher than with other
rotating machinery. The primary failure points include thrust bearings, timing gears,
and rotor assemblies.
In many cases, these mechanical failures are caused by the instability discussed in the
preceding sections, but poor maintenance practices are another major cause. See the
troubleshooting guide in Table 10–9 for rotary-type, positive-displacement compres-
sors for more information.
10.3 CONVEYORS
Conveyor failure modes vary depending on the type of system. Two common
types of conveyor systems used in chemical plants are pneumatic and chain-type
mechanical.
10.3.1 Pneumatic
Table 10–6 lists common failure modes associated with pneumatic-conveyor systems;
however, most common problems can be attributed to either conveyor piping plug-
ging or problems with the prime mover (i.e., fan or fluidizer). For a centrifugal fan
troubleshooting guide, refer to Table 10–4. For fluidizer and blower guides, refer to
Table 10–5.
10.3.2 Chain-Type Mechanical
The Hefler-type chain conveyor is a common type of mechanical conveyor used in
integrated chemical plants. Table 10–7 provides the more common failure modes of
this type of conveyor. Most of the failure modes defined in the table can be directly
attributed to operating practices, changes in incoming product quality (i.e., density or
contamination), or maintenance practices.
10.4 COMPRESSORS
Compressors can be divided into three classifications: centrifugal, rotary, and recip-
rocating. This section identifies the common failure modes for each.
10.4.1 Centrifugal
The operating dynamics of centrifugal compressors are the same as for other cen-
trifugal machine-trains. The dominant forces and vibration profiles are typically iden-
