Glossary A

Our definitions are intended to give our readers basic understanding
of the terms in our Glossary. Some national and industry standards, or
customer specifications, may have specific definitions of certain terms
that might be different from their common usage - in which case the
terms should be interpreted in the context of the relevant standards, or
specifications, being referenced to.

Acceleration - the time rate of change of velocity. In harmonic motion, acceleration
leads velocity by 90 degrees in time, and leads displacement by 180 degrees in

Accelerometer - a seismic transducer that is commonly used in vibration
measurement and monitoring. It converts acceleration motion, or gravitational
forces capable of causing acceleration, into a proportionate electrical signal.

Acoustic - pertaining to the speed, or frequency, of sound waves.

Acoustic resonance - the state of being very close to the speed, or frequency, of
sound waves. When the frequency of a vibrating object, such as a shaft, is very
close to the frequency of sound waves being reflected from a surface, such as the
volute, the vibrating object is considered to be in acoustic resonance with the
sound wave. The resonance would have the detrimental effect of amplifying the
vibration level that can result in a catastrophic damage to the equipment.

A-gap - the radial gap between the outer diameter (OD) of an impeller and the
case bore adjacent to the volute tongue. A tight A-gap can be a contributing factor
in amplifying the vibration of a pump, whereas an oversize A-gap can be a point
where discharge flow recirculation may occur.

Air leak test

Affinity laws - the mathematical expressions that define the changes in pump
capacity, differential head, and brake horsepower (BHP) when a change is made
to the impeller diameter, or pump speed.

Alignment - a condition where the axes of interconnecting parts, or components,
are co-linear, parallel, or perpendicular to one another in accordance with their
intended design.

Angular contact ball bearing - ball bearing with steep contact angle designed to
carry heavy thrust load in one direction. Bi-directional thrust can be handled by  
arranging two bearings in back-to-back position.

Anti-rotation device - A piece, such as a pin or key, used to prevent one part from
rotating relative to an adjacent part such as those found in a case ring, sleeve, or
in mechanical seal assembly.

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