referring to fig1 - 3 , the basic design of the check valve 10 of the invention comprises a sleeve - like integral valve body 12 having a central axial passageway 14 therethrough defining input 16 and output 18 . an integral valve element or poppet 20 is reciprocatingly positioned within passageway 14 . the valve element 20 comprises a reduced diameter portion 22 and an increased diameter portion 24 joined together at a forwardly converging frustro - conical valve seat 26 . correspondingly , the lumen of the axial passageway 14 comprises a reduced diameter portion 28 and an increased diameter portion 30 joined at a forwardly converging frustro - conical valve seat 32 . valve element 20 is positioned within the axial passageway 14 such that its valve seat 26 is matable against the seat 32 of the body 12 to create an airtight seal therebetween . the increased diameter portion 30 of the axial passageway 14 comprises a plurality of longitudinal flutes 34 along a portion of the length thereof . correspondingly , a plurality of longitudinally extending lands or ribs 36 are longitudinally formed on a portion of the outside surface of the increased diameter portion 24 of the valve element 20 . however , the number of flutes 34 is different than the number of lands 36 such that the lands 36 , combined with the flutes 34 , function to centrally locate the valve element 20 within the axial passageway 14 . hence , a more adequate seal is obtained between the respective seats 26 and 32 , as more particularly described in u . s . pat . no . 3 , 831 , 629 , the disclosure of which has been incorporated by reference herein . further , the increased diameter portion 24 of the valve element 20 comprises an axial blind hole 38 therein to produce a resilient annular wall 40 capable of flexing when pressure is exerted on the end of the valve element 20 . as described more completely below , the valve element 20 is retained in position within the axial passageway 14 by means of an insertable plug 42 which is properly dimensioned relative to the length of the increased diameter portion 24 of the valve element 20 to compressibly force the seat 26 of the valve element 20 into sealing engagement with the seat 32 of the valve body 12 at a pressure hereinafter referred to as the cracking pressure . more particularly , referring to fig1 plug 42 comprises a symmetrical design such that the plug 42 can be inserted in the passageway 14 without concern for proper orientation during assembly . the symmetrical plug 42 comprises an annular ring 44 which is engagable within a corresponding annular slot 46 formed within the lumen of the sleeve - like valve body 12 . a pair of diametrical vanes 48 and 50 , positioned ninety degrees with respect to one another , are integrally formed within the annular ring 44 such that fluid flowing through the passageway 14 flows through the four quadrants or apertures defined by the respective vanes and the annular ring 44 . each of the vanes 48 and 50 comprises a lower annular platform portion 52 and an upper annular platform portion 54 joined at sloping edge 56 . the lower corner 58 formed between the sloping edge 56 and the lower platform portion 52 is formed at a diameter substantially equal to the diameter of the blind hole 38 of the valve element 20 . with such dimensions , it should be appreciated that the sloping edge 56 of the vanes 48 and 50 of the plug 40 function to centrally locate the rearward end of the valve element 20 within the axial passageway 14 of the check valve 10 . further , the lower annular platform portion 54 provides a flat surface in engagement with the flat rear face 60 of the valve element 20 thereby stablizing the valve element 20 in position within the axial passageway 14 . the check valve 10 of the invention is assembled by simply inserting the valve element 20 into the axial passageway 14 and then snapping into place the plug 42 into the axial passageway 14 until the plug &# 39 ; s annular ring 44 engages into annular slot 46 . the distance or height of the lower annular platform portion 52 relative to the center of the annular ring 44 of the plug 42 , as represented by dimension &# 34 ; h &# 34 ; in fig1 functions to determine the distance between the lower annular platform portion 52 and the valve seat 32 of the valve body 12 . consequently , it should be readily appreciated that increased height h increases the cracking pressure needed to unseat the respective valve seats 26 and 32 . conversely , decreased height h functions to decrease such cracking pressure to a decreased amount . indeed , height h can be decreased by such a degree that the valve element 20 freely floats within passageway 14 thereby causing the check valve 10 to operate as a conventional check valve with no cracking pressure needed for fluid to flow from the input 16 to the output 18 of the check valve 10 . from the foregoing , it is apparent that the valve body 12 and the valve element 20 may be produced from single sized injection molds utilizing conventional injection molding techniques . however , various plugs 42 may be produced in different injection molds to produce a variety of plugs 42 having different heights h . thus , during assembly , various check valves 10 , each having different cracking pressures , may be assembled by using the appropriate plug 42 , thereby maintaining a one - size supply of valve bodies 12 and valve elements 20 . thus , a large variety of check valves having different cracking pressures may be economically supplied to customers without requiring the manufacturer to maintain a large inventory of otherwise different sized valve bodies 12 or valve elements 20 . fig2 illustrates a second embodiment of the check valve 10 in which sleeve - like valve body 12 comprises an extended output end 62 which is crimped inwardly as illustrated to produce a bullet - shaped end . additionally , the second embodiment of the check valve 10 comprises an annular flanged mounting 64 extending about the central portion of the valve body 12 . the second embodiment of this check valve 10 is particularly useful in conjunction with plastic tubing . specifically , the bullet - shaped end 62 of output 18 allows the check valve 10 to be easily inserted into the end of the tubing ( not shown ) until the end of the tubing is engaged under the flanged mounting 64 . the flanged mounting 64 may then be crimped to securely retain the check valve 10 to the end of the tubing . a more complete disclosure of various types of flanged mountings 64 is disclosed in u . s . patent application , ser . no . 450 , 453 , filed dec . 16 , 1982 , entitled &# 34 ; self - retaining check valve and mounting therefor &# 34 ;, which has been assigned to the assignee of this application , the disclosure of which is hereby incorporated by reference herein . finally , fig3 illustrates the third embodiment of the check valve 10 of the invention in which the plug 42 comprises an asymmetrical design having a pair of perpendicularly disposed vanes 48 and 50 integrally formed within an annular ring 44 . however , vanes 48 and 50 comprise , on the inward side of the annular ring 44 , only one annular platform portion 66 whereas vanes 48 and 50 extending on the outward side of the ring 44 comprise a sloped , bullet - shaped configuration 68 . while symmetry and thus , ease during assembly is eliminated , the bullet - shaped edge 68 of the vanes 48 and 50 allows the check valve 10 to be easily inserted into a tubing . although not illustrated , the third embodiment of the check valve 10 may also include a flanged mounting as shown in fig2 and disclosed in said patent application referenced herein without departing from the spirit and scope of this invention . the present disclosure includes that contained in the appended claims , as well as that of the foregoing description . although this invention has been described in its preferred form with a certain degree of particularity , it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit of the invention .