Page 203 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

The single, outside-mounted, unbalanced seal

This type of seal has the rotary component and face mounted outside
the seal chamber. The springs and drive elements are outside the
pumped liquid. This reduces the problems associated with corrosion
and the accumulation of pumped product clogging the springs. This
seal is popular in the food processing industry. The pumped liquid
arrives to the inside diameter of the faces and seals toward the outside
diameter. The environment outside the pump approaches the OD of
the face union. Pressures are limited to about 35 psig. Sometimes this
seal can be mounted either inside or outside the pump. This seal is easy
to install, adjust, and maintain. It permits easy access and cleaning of
the pump internal parts, often required in the food processing industry.

The single, balanced, internal mechanical seal

This balanced seal varies the face loading according to the pressure
within the pump. This extends the pressure limits of the seal (Figure
13-6).
The earlier balanced seals incorporate stepped faces mounted onto a
stepped sleeve or shaft. Later models offer the balance effect without
stepping arrangements. The pumped liquid approaches the OD of the
seal’s faces with atmospheric pressure at the ID of the faces. These seals
are good in the 500 to 600 psig ranges, and they generate less heat than
their unbalanced versions. They’re popular in petroleum refining, and
in general industry where some liquids are prone to easy vaporization.

Figure 13-6

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