Stonewall

The point on a centrifugal compressor performance curve in which the maximum flow and minimum polytropic head is encountered, beyond which further decreases in network resistance will not increase the flow rate. This physical phenomenon occurs when the gas velocity has increased to the local acoustic velocity, or Mach 1, at some point in the compressor. Stonewall is not particularly damaging to single-stage centrifugal compressors but can cause serious damage to the rotors and blades of multistage centrifugal and axial compressors.

Also known as Choke Point.