a throttle lever 200 which is normally provided and controls flow of fuel in the operation of the engine 10 when the throttle lever 200 is displaced the mechanical connections 198 194 open the valve 190 to bleed air from the manifold 74 upon completion of the accleration mode or after the rate of acceleration is reduced below a given level the function generator 196 acting through the mechanical connection 194 causes the valve 190 to close returning the interconnected slot means to the mode of operation previously described the result is to provide an improvement on the showing of conrad german pat no 1 938 132 and o 39 connor u s pat no 3 768 919 in that for most operating conditions the closed manifold alone will prevent initiation of surge however during emergency acceleration of the engine pressure surges can be bled off and stable operation achieved by limiting bleed to the relatively short duration required for acceleration there is a minimal effect on overall compressor efficiency of greater importance is the fact that relatively small amounts of bleed flow produce very significant increases in the operating range and thus provide a greatly increased margin of safety at a time when surge is most likely to occur in the preceding description reference has been made to specific forms of compressors employed in gas turbine engines for pressurizing air in the generation of a high energy hot gas stream the broader aspects of the invention are not so limited but are applicable to any form of rotary compressor for compressible fluids.