What is critical speed when referred to a pump?
A. Critical speed is one or more speed values that coincide with a natural frequency of vibration of the pump rotor or structure. A resonant condition can result when the operating speed or vane-pass frequency of the pump excites the structure’s natural frequency. At resonance, the vibration levels will be amplified depending on the amount of damping present in the system. Much attention is often given to the value of the natural frequency of the pump assembly; however, in a field installation, the structure comprises-in addition to the pump-the foundation, the mounting, the piping and its supports, and may include the driver and coupling or driveshaft(s), as applicable. The natural frequency of the total structure may therefore differ significantly from the natural frequency of the pump alone. The system designer should consider this to ensure an appropriate separation margin exists between the system’s natural frequency and the operating speed. For systems that operate over a speed r
