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Glossary B
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The following definitions are intended to give basic understanding of the terms
commonly used in the pump industry. Some industry standards, or customer
specifications, may have specific meaning of certain terms that may be different
from their common usage - in such case the terms should be interpreted in the
context of the standards, or specifications, being referred to.
B-gap - The radial gap between the impeller outside diameter (OD) and tip of
clearance or cutwater clearance. Inadequate B-gap may result in high vibration
level at impeller vane pass frequency especially with high energy density
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 pressure -

Back shroud -

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 face-to-face.

Back wear ring -

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 bearings -

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 -

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 vertical
canned-pump.

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.

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.

Baseplate -

Bellows seal - A mechanical seal that has a flexible metal bellows for providing
secondary sealing and spring-type loading.

BEP or B.E.P. - see Best Efficiency Point.Best efficiency point (BEP) - Best
efficiency point (BEP) is the capacity at maximum impeller diameter at which the
pump efficiency is highest. The BEP is an important parameter because many
terms such as specific speed, suction specific speed, hydrodynamic size,
minimum flow, viscosity correction, etc., are calculated based on the capacity at
BEP.

Beta version - in a state of trial run to find out and correct errors; in an
unfinished condition and undergoing review and changes. This web site is in
beta version in its entirety.

Between-bearing pump - a pump whose rotating element is supported by two
thrust bearing housings located on opposite ends of the shaft. The impeller is
located in-between two thrust bearing assemblies.

Blade - same as vane.

Blade pass frequency - the frequency corresponding to the number of blades
of an impeller multiplied by the impeller rotating speed. Example, an impeller with
seven blades rotating at 1780 RPM has a blade pass frequency of 7 x 1780 =
12,460 cycles per minute. In a multistage rotor with different impellers, each
impeller has a unique blade pass frequency depending on its number of blades.
Many pump vibrations occur at impeller blade pass frequency. Also known as
vane pass frequency.

Blank piece

Blistering -

Buffer liquid - a liquid injected as a lubricant or buffer between unpressurized
tandem mechanical seals. The pressure of the buffer liquid is always lower than
that of the process liquid being sealed. See barrier liquid.

Bundle – slang for the inner case assembly of a barrel pump.

Butterfly valve - a type of control valve with rotating vane used in services
where low pressure drop in the fully open position is important, and where small
size and light weight are also essential. It is commonly provided with synthetic
rubber seating surfaces to ensure tight  shutoff in the closed position.
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