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 time.
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.
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.