Page 86 - Root Cause Failure Analysis

PUMPS

Pumps are designed to transfer a specific volume of liquid at a particular pressure
from a fixed source to a final destination in a process system. A pump’s operating
envelope is defined either by a hydraulic curve for centrifugal pumps or a pressure-
volume (PV) diagram for positive-displacement pumps.

CENTRIFUGAL
Centrifugal pumps are highly susceptible to variations in process parameters, such as
suction pressure, specific gravity of the pumped liquid, back pressure induced by con-
trol valves, and changes in demand volume. Therefore, the dominant reasons for cen-
trifugal pump failures usually are process related.

Several factors dominate pump performance and reliability: internal configuration,
suction condition, total dynamic pressure or head, hydraulic curve, brake horsepower,
installation, and operating methods. These factors must be understood and used to
evaluate any centrifugal pump-related problem or event.

Configuration
All centrifugal pumps are not configured alike. Variations in the internal configuration
occur in the impeller type and orientation. These variations have a direct impact on a
pump’s stability, useful life, and pedormance characteristics.

Impeller Type
A variety of impeller types are used in centrifugal pumps. They range from simple
radial flow, open designs to complex variable-pitch, high-volume, enclosed designs.
Each type is designed to perform a specific function and should be selected with care.

77