Glossary B

B-gap - The radial gap between the impeller outside diameter (OD) and tip of
volute lip (or diffuser lip in a diffuser pump).  It is also referred to as the volute lip
clearance or cutwater clearance.

Inadequate B-gap may result in high vibration level at impeller vane pass
frequency especially with high energy density centrifugal pumps.

BA - The width of the impeller opening at its outside diameter (OD). It is the width
of the impeller at its OD excluding the impeller shroud (wall) thickness.

The impeller BA is a significant parameter because it is proportional to the pump
capacity, and it also proportional to its hydraulic radial load.

Back-to-back - When referring to impellers, a back-to-back arrangement is when
two adjacent impellers in a two-stage or multistage pump, are arranged so that
the backs of the impellers are adjacent to each other, and their suctions are on
opposite sides facing away from each other.

When referring to ball thrust bearings, a back-to-back arrangement is when two
adjacent bearings are arranged so that the back, or high shoulder of the of the
outer rings, are next to each other. The bearing contact angles
diverge inward to
the shaft. See definition of

Base circle - A reference circle in a volute development that is used as a basis for
sizing the volute cutwater diameter. The base circle diameter usually corresponds
to the maximum impeller diameter for which a volute is designed for.

"Bad actor" pump - The term used to a pump whose mean time between failures
(MTBF) is so poor that the pump suffers from chronic failures and high operating
and maintenance cost.  A "bad actor" pump is a prime candidate for hydraulic
re-rate or mechanical upgrade.

Balanced seal - A mechanical seal arrangement where the seal is designed to
change the effect of the hydraulic pressure in the seal chamber on the seal face
closing force, typically based on the seal balance ratio of less than 1.

Ball shuttling - A phenomena whereby balls in an inactive, or unloaded, bearing
rotate perpendicular to their rolling axis due to gyroscopic forces causing them to
lose contact with the raceway momentarily. Ball shuttling can cause premature
bearing failure due to the acceleration of microscopic wear, and is characterized
by the appearance of polished or burnished raceway. Also known as
ball sliding.

Ball sliding - See ball shuttling.

Barrel pump - A horizontal pump of a double casing type consisting of an inner
casing and an outer barrel. The inner casing, containing the rotor, is under
compressive pressure from the liquid in the barrel which is under full discharge
pressure. A similarly designed vertical pump is usually referred to as

Barrier liquid - a liquid injected between pressurized double mechanical seals to
isolate the process liquid from the atmosphere. The pressure of the barrier liquid
is always higher than that of the process liquid being sealed. See
buffer liquid.

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