Peripheral speed is the speed at the periphery of a circular part due to its rotation. It has both magnitude and direction (circular) and should be more aptly referred to as peripheral velocity, but the term peripheral speed has been more widely used. It is calculated using the equation:
S = [ D x N ] / 229
S - peripheral speed (or peripheral velocity), feet per second (FPS) D - outer diameter of part under consideration, inches N - rotational speed, revolutions per minute (RPM)
What is the peripheral speed of a 10-inch diameter impeller rotating at 3560 RPM?
S = [ 10 x 3560 ] / 229 = 155 FPS
The design, operation, or performance of some rotating pump parts are affected by their peripheral speeds so it is important that their magnitudes are known:
impeller outer diameter - It determines the head it develops, and affects its material selection. Slurry service requires low peripheral speed, etc.
impeller eye diameter - It determines the pump NPSHR, and affects the onset of suction flow recirculation, etc.
anti-friction (ball) bearings - They have limited speed and, typically, are not used in high speed pumps.
sleeve, or journal, bearing - It determines the type of bearing to be used, and its type of lubrication system - the amount of lubrication, heat transfer, etc.
mechanical seal - It affects the required amount of cooling and lubrication.
impeller wear ring - Its peripheral speed affects the manner of mounting, or securing, the wear ring into the impeller shrouds.
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