A very basic description of the surging phenomenon is that the gas streamlines normally at the diffuser entrance and sometimes at the impeller eye to exhibit a high incidence angle and stall, not unlike an airplane going into a sudden climb. When the stall is reached, the gas in the compressor ceases to flow forward in he compressor and a reverse flow takes place. The reverse flow collides with the forward flow, making the noise one hears when a centrifugal compressor goes into surge. This phenomenon is accompanied by a sudden rise in discharge temperature. Surge prevention can be accomplished by bypassing discharged cool gas back to the inlet using an amply sized valve. The quantity of gas must be equal to the surge flow (taken from the compressor pressure volume curve plus a small margin, such as 10%).