62 fig2 a series of pairs of male and female compression pockets are formed by the housing assembly 22 male rotor body 30 and female rotor body 34 each compression pocket is bounded by external surfaces of enmeshed rotors by portions of cylindrical surfaces of male and female rotor bore surfaces in the rotor case and continuations thereof along a slide valve and portions of face 57 fig2 shows further details of the exemplary flowpath at the outlet discharge port 58 a check valve 70 is provided having a valve element 72 mounted within a boss portion 74 of the outlet housing 56 the exemplary valve element 72 is a front sealing poppet having a stem shaft 76 unitarily formed with and extending downstream from a head 78 along a valve axis 520 the head has a back underside surface 80 engaging an upstream end of a compression bias spring 82 e g a metallic coil the downstream end of the spring engages an upstream facing shoulder 84 of a bushing guide 86 the bushing guide 86 may be unitarily formed with or mounted relative to the housing and has a central bore 88 slidingly accommodating the stem for reciprocal movement between an open condition of fig2 and a closed condition of fig3 the spring 82 biases the element 72 upstream toward the closed condition in the closed condition an annular peripheral seating.