seals 21 and 26 and the check valve flange 13 all together when the band clamp 30 is tightened an inner annular ridge 22 is formed on the first flange 20 and extends to hold the seal 21 in place relative to the first flange 20 an annular ridge 27 extends from the second duct flange 25 and retains the seal 26 in position on the second duct flange 25 if both the first and second duct flanges 20 25 need to be indexed to the check valve 15 then both duct flanges 20 and 25 need to include void areas 41 a 41 b 41 c and 43 a 43 b 43 c in both the outer annular ridge 23 and in the annular ridge 27 respectively to receive the index tab 16 a now referring to fig3 of the drawings a cross section of a portion of the check valve assembly of fig1 is shown where the check valve is shown in a rotational position such that fig3 does not show the primary or secondary index tabs 16 a 16 b 16 c or primary or secondary index fingers 17 a 17 b 17 c extending from the first flange 20 is an annular ridge 22 and an outer annular ridge 23 where the inner annular ridge 22 retains the seal 21 in position on the first flange 20 because there is not a primary index tab 16 a or secondary index tabs 16 b 16 c in this particular orientation of the check valve assembly 10 there is an outer annular edge shown 23 and not one of the void.