MIXERS AND AGITATORS
Mixers are devices that blend combinations of liquids and solids into a homogenous
product. They come in a variety of sizes and configurations designed for specific
applications. Agitators provide the mechanical action to keep dissolved or suspended
solids in solution.
Both operate on basically the same principles, but variations in design, operating
speed, and applications divide the actual function of these devices. Agitators generally
work just as hard as mixers, and the terms often are used interchangeably.
There are two primary types of mixers: propeller/paddle and screw. Screw mixers can
be further divided into batch and mixer-extruder types.
Propeller/paddle mixers are used to blend or agitate liquid mixtures in tanks, pipelines,
or vessels. Figure 1 1-1 illustrates a typical top-entering propeller/paddle mixer. This
unit consists of an electric motor, a mounting bracket, an extended shaft, and one or
more impeller(s) or propeller(s). Materials of construction range from bronze to stain-
less steel, which are selected based on the particular requirements of the application.
The propeller/paddle mixer also is available in a side-entering configuration, which is
shown in Figure 11-2. This configuration typically is used to agitate liquids in large
vessels or pipelines. The side-entering mixer is essentially the same as the top-enter-
ing version except for the mounting configuration.
Both the top-entering and side-entering mixers may use either propellers, as shown in
the preceding figures, or paddles, as illustrated by Part b of Figure 11-3. Generally,
Root Cause Failure Analvsis
Figure 11-1 Top-entering propeller-type mixer (Thomas Register 1995).
Figure 11-2 Side-entering propeller-type mixer (Thomas Register 1995).
Mixers and Agitators
Figure 11-3 Mixer can use either propellers or paddles to provide agitation (Thomas Regis-
propellers are used for medium- to high-speed applications where the vi