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Bulletin board

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Glossary B

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.
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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 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.

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.

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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