between slugs is filled by entrainment fluid 72 entering at induction port 74 through backflow preventer and control valve 76 one familiar with the operation of ejectors and jet pumps will realize that the entrainment fluid induction method as well as the suction chambers of both of the herein described embodiments though appearing diagrammatically different are physically the same embodiment this fact may be seen more clearly in fig4 fig4 inculcating the method and mechanics of the variable volume ejector shown in fig2 a contains an innovation designed to eliminate backflow preventer means 76 of fig3 the apparatus downstream of air induction ports 76 39 operates on the same principle after hydraulic slug formation as iris valve 34 and chambers 42 and 44 of fig2 a therefore the inlet pulsing means embodied herein will be discussed attention is now called to fig4 at the point of induction of motive fluid 68 the familiar cylinder within cylindrical chamber pulser is used in a slightly different configuration inlet apertures 64 66 are larger than those of fig3 this is because the constriction 70 of fig3 has been eliminated so that a rotating inner pulser cylinder 60 may employ induction ports 76 and terminate at iris valve 34 while maintaining a consistent cross sectional area with stage 11 ejector tube chambers 42 44 although a discrete constriction has not been employed nonetheless constricting is effected by using motive fluid intake aperturing having greater cross sectional area than the downstream inlet ejector tubing relative constriction ibid the latter design alternative may in.