Definitions for

**"Critical speed"**Any object made of an elastic material has a natural period of vibration. When a pump rotor or shaft rotates at any speed corresponding to its natural frequency, minor unbalances will be magnified. These speeds are called the critical speeds.

Rotative speeds at which rotating machinery-axial or screw lobe-pass through unbalanced operation.( 03012)

(of a rotating mechanical system) Is that speed at which torsional vibration excitation from rotating components is equal to a natural frequency of the system. The torsional vibration frequency will be equal to the speed multiplied by the order number. (See definition) As an example, a 4-cycle, 4-cylinder in-line engine with an order number of two operating at 1,000 RPM would generate a frequency of excitation of 33 Hz (2 x 1,000/60 sec/min). If the natural frequency of the system is also 33 Hz, then the critical speed, for that system, would be 1,000 RPM.