Page 249 - Intro Predictive Maintenance

240 An Introduction to Predictive Maintenance

on a common crankshaft. The interrelationship and magnitude of these two effects
depend on such factors as number of cranks, longitudinal and angular arrangement,
cylinder arrangement, and amount of counterbalancing possible. Two significant
vibration periods result, the primary at the compressor’s rotation speed (X) and the
secondary at 2X.

Although the forces developed are sinusoidal, only the maximum (i.e., the amplitude)
is considered in the analysis. Figure 10–1 shows relative values of the inertial forces
for various compressor arrangements.

10.5. MIXERS AND AGITATORS
Table 10–11 identifies common failure modes and their causes for mixers and agita-
tors. Most of the problems that affect performance and reliability are caused by
improper installation or variations in the product’s physical properties.

Proper installation of mixers and agitators is critical. The physical location of the vanes
or propellers within the vessel is the dominant factor to consider. If the vanes are set
too close to the side, corner, or bottom of the vessel, a stagnant zone will develop that
causes both loss of mixing quality and premature damage to the equipment. If the
vanes are set too close to the liquid level, vortexing can develop. This causes a loss
of efficiency and accelerated component wear.

Variations in the product’s physical properties, such as viscosity, also cause loss of
mixing efficiency and premature wear of mixer components. Although the initial selec-
tion of the mixer or agitator may have addressed the full range of physical properties
expected to be encountered, applications sometimes change. Such a change may result
in the use of improper equipment for a particular application.

10.6 DUST COLLECTORS

This section identifies common problems and their causes for baghouse and cyclonic
separator dust-collection systems.

10.6.1 Baghouses
Table 10–12 lists the common failure modes for baghouses. This guide may be used
for all such units that use fabric filter bags as the primary dust-collection media.

10.6.2 Cyclonic Separators
Table 10–13 identifies the failure modes and their causes for cyclonic separators.
Because there are no moving parts within a cyclone, most of the problems associated
with this type of system can be attributed to variations in process parameters, such as
flowrate, dust load, dust composition (e.g., density, size), and ambient conditions (e.g.,
temperature, humidity).