What is stone wall effect in compressor?

The term stonewall refers to the condition when the compressor fails to develop any head, as the suction volumetric flow is too high for a given RPM. (Recall that, typically, the head drops off as suction flow increases for a given RPM. Eventually, the head v/s suction flow curve becomes nearly vertical at the stonewall flow.)

Stonewall or Choke - occurs under one of 2 conditions. Typically for high speed equipment, as flow increases the velocity of the gas/fluid can approach the gas/fluid's sonic speed somewhere within the compressor stage. This location may occur at the impeller inlet "throat" or at the vaned diffuser inlet "throat".