fig1 shows a one plunger fuel pump 10 having a substantially cubic housing or body 12 , with the fuel inlet connector 14 projecting from the right , the single plunger actuation assembly 16 projecting from the left , and the inlet control valve 18 projecting from the top . with reference now to fig1 and 2 , it is readily understood that the engine drive shaft carries a lobed cam ( not shown ) that reciprocates the remote end 20 of the pumping plunger 22 within a pumping sleeve 24 secured to the housing , between fuel charging ( intake ) and discharging ( output ) phases . the other , pumping end 26 of the plunger is situated in the pumping chamber 28 , which fills with fuel at a feed pressure of up to about 4 bar during the charging phase and , preferably subject to initial spill control , pressurizes the fuel in the pumping chamber up to about 200 bar for delivery via a discharge fitting 30 to , e . g ., the common rail ( not shown ). the fuel is fed directly to the pumping chamber 28 through a solenoid controlled inlet valve 18 . as used herein , “ inner ” and “ outer ” refer to directions toward and away from the pumping chamber , respectively . the substantially cylindrical pumping plunger 22 is carried concentrically in the plunger sleeve 24 , which at one end 32 bears on or is otherwise sealed against the end wall 34 of the plunger assembly mounting bore 36 in the housing , and which must be laterally fixed directly or indirectly to the mounting bore . a plunger sleeve retainer 38 is press fit or threaded against the mounting bore wall 40 for this purpose . the plunger 22 is disposed concentrically in the inner wall 40 of the sleeve 24 and the retainer 38 . a plunger return spring 42 is captured between a spring seat 44 at the driven end 20 of the plunger and a shoulder 46 on the sleeve retainer . the outer end 48 of the plunger sleeve retainer is turned inward to capture a lip seal 50 for sealing fuel within the pump . the upper end of the retainer forms a shoulder 52 . any leakage around the inner end 32 of the plunger sleeve 24 enters the clearance 54 with the id of the tubular body of sleeve retainer 38 and is directed back to the lower pressure at the inlet valve 18 , via leak off ports 56 in the retainer and an internal passage 58 through the housing . in the embodiment of fig1 - 3 , the sleeve 24 has an enlarged inner end portion 60 adjacent the pumping chamber 28 and a tubular body portion 62 extending to an outer end 64 . the inner end has a sealing rim or bead 66 that is urged against the sealing surface at the end wall 34 of the bore in the housing that receives the sleeve retainer and sleeve . this sealing surface surrounds the plunger near the pumping chamber and when properly sealed prevents pumped fuel from leaking along the outer surface of the sleeve and sleeve retainer . the body 62 of the sleeve is situated within the cylindrical inner wall 68 of the sleeve retainer , whereas the enlarged portion 60 at the inner end of the sleeve is formed with an integral flange or otherwise defines a downward facing shoulder 70 that axially registers with and is spaced 72 from the inner end 52 of the retainer . a load ring 74 is situated between the inner end 52 of the retainer and the shoulder 70 on the sleeve . the sleeve 24 floats on the load ring 74 until the retainer 38 is advanced within the housing bore 36 a sufficient distance to press the sealing rim or bead 66 of the sleeve against the sealing surface 34 at the end wall of the bore . when this condition is reached during assembly , the retainer is fixed with respect to the bore . this can be achieved with a threaded connection between the retainer and the bore , or the retainer can be press ( interference ) fit . the shape of the load ring affords considerable tolerance on the effective positioning of the retainer within the bore . the reason for the load ring as opposed to traditional threaded clamping or press - fit designs is to reduce the sleeve id distortion at the critical interface with the plunger od . the load ring applies a very consistent , predictable load . fig3 shows the preferred load ring 74 , and fig4 shows such ring in an alternative to the integral shoulder flange 70 , which would typically have a machined face for interacting with the load ring . according to the embodiment of fig4 , the machined face is replaced with a snap ring 76 and washer 80 . the sleeve 24 ′ has a circumferential groove 82 to receive and retain the snap ring . with the latter embodiment , less material is required to fabricate the sleeve . the load ring 74 is preferably a split or c - shaped ring having a cross section ( taken parallel to the axis 84 ) that generally resembles the letter “ w ”. the load ring can , however , be a full ring . preferably , each outer leg 86 , 88 ( at the axial ends ) is substantially perpendicular to the axis 84 with all the corners 90 , 92 , 94 contoured rather than sharp . the legs are spaced apart a free height h when the ring is not loaded , but move toward each other during loading by the sleeve retainer 38 , to a shorter , compressed height h ′. in a typical application , the load ring can be 20 - 25 mm across the greatest diameter ( at 92 ), and 4 to 5 mm less across the smallest diameter ( at 90 , 94 ), for axially transmitting a target seal load of 750 - 1500 lbs . across a surface area defined by the legs , in the range of 0 . 0001 to 0 . 0002 m 2 . as a representative but not limiting example , the free height h of the load ring can be about 4 . 0 mm , whereas the compressed height h ′ for transmitting the target load can range between about 2 . 0 to 3 . 0 mm ( i . e ., a compression of about 1 - 2 mm ). as noted above with reference to fig2 , any leakage past the seal at 66 is at a low pressure and passes through ports 56 in the retainer 38 into the passage 58 leading to a low pressure volume such as at the inlet valve . any other potential leakage is blocked by an o - ring 98 or the like situated between an enlarged diameter portion of the retainer outside the leak off port 56 , and a similarly enlarged portion of the housing bore . fig5 is an exploded view of the embodiment of fig4 , with like structure indicated by like numerals . the inlet fitting assembly 14 forms no part of the present invention , but preferably has a bellows type inlet pressure attenuator such as described in the priority patent application . the inlet valve assembly 18 may be of any conventional type , preferably solenoid controlled . additionally to the structure previously described with respect to fig1 - 4 , fig5 shows an overpressure check valve assembly 100 . the lip seal 50 at the outer end of the plunger is shown separated from its retainer 102 . it is well within the ordinary skill in the art to select an appropriate check valve assembly between the pumping chamber 28 and the discharge fitting 30 . in the version shown in fig2 and 5 , a spring 104 has a cap 106 and a seat 108 , aligned with ball 110 and another seat 112 . also shown is another o - ring 114 for placement in a groove on the neck of the housing , where the housing is mounted to the engine . while preferred embodiments have been set forth for purposes of illustration , the foregoing description should not be deemed a limitation of the disclosure herein . accordingly , various modifications , adaptations and alternatives may occur to one skilled in the art without departing from the spirit and scope of the present disclosure .