as shown in fig1 a multi - stage automotive fuel pump includes a casing 12 having a motor and pumping elements installed therein . accordingly , motor 14 contained within casing 12 has a driveshaft 16 extending from the motor such that the motor powers the two rotary pumping elements . primary rotary pumping element 18 comprises a regenerative turbine which is attached to and which rotates with driveshaft 16 . rotary pumping element 18 comprises a portion of a primary pumping section , with the remainder of the pumping section comprising primary intake 19 which picks up fuel from the liquid surrounding the pump within the vehicle &# 39 ; s fuel tank or , if pump 10 is externally mounted , from a line extending into the fuel tank . the primary pumping section further includes a primary pump housing , which is defined by lower pump housing 20 and by center housing 22 , which comprises a generally disk - shaped body with two parallel faces , and which has a cup - shaped opening 22a into which primary rotary pumping element 18 is inserted . center housing 22 also has annular pumping channel 22b formed therein ( fig6 ), which corresponds to an annular pumping channel 20a formed in the opposing face of lower pump housing 20 . the second rotary pumping element of a pump according to the present invention in this case comprises a gerotor element 26 which is nestled in a cup - shaped space 24a formed in upper pump housing 24 . the secondary pumping section of the present pump is of course powered by motor 14 by means of driveshaft 16 . as before , the secondary pumping section includes a pump housing and pumping element . upper pump housing 24 and center housing 22 define a secondary pump housing for gerotor secondary rotary pumping element 26 . fuel passing through pump 10 of fig1 enters primary intake 19 and is pumped initially by regenerative turbine rotary pumping element 18 . having been pumped by element 18 , the fuel is further pumped by gerotor secondary rotary pumping element 26 . in a pump according to the present invention , a high level efficiency is maintained because the transfer of fuel between primary rotary pumping element 18 and secondary rotary pumping element 26 is managed efficiently and smoothly with minimized turbulence and cavitation . of course , as with most rotary machines , seemingly insignificant losses in efficiency for various sections of the pump will greatly impair the overall efficiency of the device . in this case , fuel transfer passage 28 ( see fig1 ), which extends through the common wall portion of center housing 22 , smoothly guides the fluid mainstream from the tangential direction to the axial direction and minimizes , as noted above , turbulence and cavitation . additional details of fuel transfer passage 28 are shown with reference to fig2 and 6 . fuel entering primary intake 19 is picked up by primary rotary pumping element 18 and progresses , as shown in fig6 in a clockwise direction beginning at point a . after rotating about the full extent of pumping channel 22b , the fuel leaves the primary pumping section via primary outlet 28a ( fig3 and 6 ). after entering primary outlet 28a , the fuel ultimately flows into the secondary inlet and pumping channel 28b , which is shown at fig2 for the pump depicted in fig1 . notice that the radius of channel 28b of fig2 is less than that depicted for pumping channel 22b of fig6 . this is because the diameter of secondary rotary pumping element 26 is less than that of primary rotary pumping element 18 . upon entering secondary inlet and pumping channel 28b ( fig2 ), liquid fuel is fed to gerotor pumping element 26 and thereafter exits the secondary pumping section via outlet 30 . as shown in fig2 secondary inlet and pumping channel 28b extends around a circular arc segment of approximately 160 ° in the direction of rotation of the secondary gerotor pumping element . the transition of fuel from the primary to the secondary rotary pumping element is eased by the construction of center channel 28c of the fuel transfer passage 28 . with reference now to fig3 primary rotary pumping element 18 is depicted as having parallel faces 18a and 18b . fuel pumped by element 18 leaves the primary pumping section by means of primary outlet 28a and flows through center channel 28c and ultimately into secondary inlet and pumping channel 28b . notice in fig3 that the central chord of center channel 28c makes an acute included angle , θ , with face 18a of rotary pumping element 18 which is 25 °- 30 °. this 25 °- 30 ° angle allows the fuel to flow smoothly from the primary to the secondary pumping sections without undue turbulence or cavitation . this flowpath is shown graphically in fig3 a . as seen from fig3 a , the flow changes from a tangential to a modified axial flow . the transfer of fluid in applicant &# 39 ; s device from the primary to the secondary pumping sections is contrasted with that of the prior art transfer flow shown in fig4 and 4a . notice in fig4 that the angle θ is approximately 90 °. as a result , the flow shown in fig4 a as leaving the primary pumping section must make approximately a right angle turn and flow purely axially from the primary pumping section to the secondary pumping section . as a result , losses are engendered to the detriment of the pump &# 39 ; s performance . the present invention overcomes this problem in the manner shown . fig5 shows a second embodiment according to the present invention in which twin regenerative turbine elements 18 and 27 , respectively , are used for the primary and secondary rotary pumping elements . as before , center housing 22 comprises a generally disk - shaped unitary body having two parallel faces and a cup - shaped depression 22a for housing primary rotary pumping element 18 . also as with the embodiment of fig1 lower pump housing 20 and center pump housing 22 define a primary pumping chamber , whereas upper pump housing 24 and center pump housing 22 define a secondary pumping chamber . fuel entering the pump at inlet 19 is first pumped by primary pumping element 18 , and after passing through fuel transfer passage 28 is then pumped by secondary pumping element 27 , before being discharged from outlet 30 . as noted previously , fig6 shows the lower side of center housing 22 -- i . e ., that face of center housing 22 which forms a portion of the primary pumping section in conjunction with primary rotary pumping element 18 and lower pump housing 20 . thus , fig6 is equally applicable to both of the embodiments of the present invention . on the other hand , fig7 illustrates the face of center housing 22 which adjoins secondary rotary pumping element 27 of the pump shown in fig5 . as shown in fig7 secondary inlet and pumping channel 28b circumscribes almost the entire circumference of center housing 22 . the angular measure θ having a magnitude similar to that shown in fig3 for the center chord of center channel 28c is generally maintained for the pump of fig5 - 7 , with a preferred value for θ being an acute included angle of approximately 27 ° for the embodiment of fig5 . as with the embodiment of fig1 center channel 28c does not comprise a purely axial passage but rather contains a component directed about the circumference of the pumping channel such that the desirable flowpath characteristic illustrated in fig3 a is maintained as fuel transits from the primary pumping section to the secondary pumping section along fuel transfer passage 28 .