What is surging?

A turbocharger is a machine which is driven by the exhaust gases of the engine. Any changes in the engine's functioning and output would affect the working of turbocharger also. One such effect on turbocharger is known as surging.
The engine is subjected to a variation in load which results in the fluctuation of exhaust gas pressure. This fluctuation of in pressure makes the turbocharger run on varying speed, which leads to many unfavorable effects on the turbocharger.

Surging of turbocharger occurs when the air pressure after the compressor is higher than the pressure compressor can internally maintain. When the pressure of the air delivered by the compressor is higher than the pressure inside the compressor a reverse flow of air is created towards the impeller and inlet of the compressor, which reduces the speed of the turbine shaft and creates noise and vibration.

Surging leads to a sharp fall in the flow and acceleration of air mainly because of the reversal pressure. This imbalance in the demand and supply also leads to heavy damage to the turbocharger