Briefly, some of the usual causes of surge (other than from machine design) are:
1. Restricted suction or discharge such as a plugged strainer.
2. Process changes in pressures or gas composition.
3. Mis-positioned rotor or internal plugging of flow passages.
4. Inadvertent speed change such as from a governor failure.
The effects of surge can range from a simple lack of performance to serious damage to the machine and/or the system. Internal damage to labyrinths, diaphragms, thrust bearing and the rotor can be experienced. Surge often excites lateral shaft vibration. It can also produce torsional damages to such items as couplings and gears. Externally, devastating piping vibration can occur causing structural damage, mis-alignment, and failure of fittings and instruments.
Surge can often be recognized by check valve hammering, piping vibration, noise, wriggling of pressure gages or ammeter on the driver. Mild cases of surge are sometimes difficult to discern.