Page 276 - Root Cause Failure Analysis

23

MIXERS AND AGITATORS

Table 23-1 identifies common failure modes and their causes for mixers and agitators.
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 equip-
ment. If the vanes are set too close to the liquid level, vortexing can develop. This also
will cause a loss of efficiency and accelerated component wear.

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

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