the present invention will now be described , by way of example only , with reference to the accompanying drawings . fig1 shows a port assembly 1 consisting of an elongated tube 2 for inserting the port into the abdomen , a cannula body 3 , a gas tap 4 and a single use seal assembly 5 . the cannula body 3 and seal assembly 5 are commonly connected to one another permanently or detachably thereby aiding production of the parts and also giving the potential for the same cannula to be used with multiple seal assemblies . fig2 shows the seal unit detached from the tube 2 . at its upper surface the unit is provided with a slot or recess 6 which enables an instrument such as an optical trocar provided with a corresponding protrusion to engage with the seal unit to maintain a desired rotational alignment between the instrument and the seal unit . fig3 illustrates the port assembly 1 in conjunction with a trocar 7 which , in use , is pushed though the cannula and seal assembly 1 . when inserted , shaft 9 of trocar 7 extends down through elongate tube 2 until the underside 11 of trocar 13 mates against the upper surface 15 of cannula body 3 . at this point the trocar tip 17 extends out of elongate tube 2 by a predetermined amount . referring to fig4 , seal assembly 1 includes the elongate ( or cannula sheath ) tube 2 to which the seal housing 19 is attached via face seal or gasket 21 . gasket 21 is provided with a circumferentially and outwardly extending lip 23 which engages with a corresponding recess in the inner wall of seal housing 19 . the attachment between cannula sheath tube 2 and seal housing 19 is of the bayonet type , inner circumferentially spaced projections ( not shown ) on the seal housing 19 engaging in slots 25 of cannula sheath tube 2 . the seal housing 19 can be first pushed down on the cannula sheath tube 2 with the projections moving along axially extending portions of the slots 25 . gas tap 4 includes a tap body 27 , which is integral with the seal housing 19 , and a lever 29 which carries an integral stop member 31 . stop member 31 engages with features located within tap body 27 to limit the range of movement of lever 29 . this assists the surgeon by indicating when the tap is in its fully open or fully closed condition . duck bill valve 33 , having an upper circumferential lip 35 , seats on a corresponding circumferential ledge located within seal housing 19 . an intermediate plate 37 locates within seal housing 19 above valve 33 . it provides a support surface 39 for the seal and also provides a lip 41 on which the bellows member ( to be mentioned below ) is mounted . located on intermediate plate 37 is lower clamp 43 which is in the form of a flat ring 45 having extending axially from one surface a series of integral pegs 47 which are equally spaced apart . these pegs 47 are all of similar shape and size , being circular in cross section , apart from one peg 49 which is key shaped in cross section . instrument seal member 51 is made from a thin flexible plastics material and includes central , flat ring 53 to which six part - circular petals 55 are integrally connected . as shown in fig4 , the seal member 51 is a planar member although , as will be described below , the petals can be folded over for use within the seal unit . ring 53 has located therein equally spaced apart holes 57 , all of which are circular apart from one which is keyhole shaped . ring 53 is for location on lower clamp 43 with pegs 47 of lower clamp 43 extending through corresponding holes 57 of ring 53 , as best seen in fig9 . each petal 55 has a part circular edge 59 and a straight edge 61 . the petals 55 are equally spaced apart about ring 53 to which each petal 55 is connected by a living hinge which is indicated at 63 located at the part circular edge of the petal close to one end of the straight edge . each petal 55 is provided with a plurality of holes 65 which are equally spaced apart and extend circumferentially and spaced inwardly from the part circular edge of the petal . as is best seen in fig9 , most of the holes 65 are circular . however , three of the petals 55 have keyhole shaped holes 67 and they are located at different positions in their respective petals for a reason that will be made clear below . located above seal member 51 is a protection or armour layer 69 which is made of flexible plastics material . as best seen in fig1 a and 11b , armour layer 69 comprises two substantially circular elements 71 and 73 interconnected at their peripheral edges by an integral living hinge 75 . both elements 71 and 73 are formed of resilient plastics which is more robust than that of seal member 51 . when located within the seal housing 19 , element 71 lies below element 73 . the protective or armour layer 69 may , instead of being a single piece , alternatively be formed of two separate elements corresponding to elements 71 and 73 shown in fig1 a . circular element 71 comprises an outer ring area 77 in which are located a series of equally spaced apart holes 79 , which are circular except for one keyhole shaped hole 81 and which are for location over the pegs 47 of lower clamp 43 . within ring area 77 are located two flaps 83 each of which is broadly semicircular in shape with a gently curved edge 85 extending between the rounded ends of a peripheral edge 87 which extends slightly inwardly and parallel to ring area 77 . the gently curved edges of the two flaps 83 face each other on either side of a line passing through the centre of circular element 71 , the space between the opposite edges 85 decreasing from a relatively wide spacing at the centre of element 71 to narrower spacings at the radially outer positions . each flap 83 is connected at its peripheral edge 87 to the ring area 77 by two spaced apart integral links 89 . this arrangement is such that the flaps 83 can be resiliently flexed out of the plane of the ring area 77 . circular element 73 is of similar configuration to that of element 71 but with its two flaps 91 being aligned at 90 ° to the flaps 83 of element 71 . each flap 91 has , adjacent its gently curved edge a strip 93 which has steeply reducing thickness from the body of the flap towards its free edge . the flaps 83 of element 71 have similar edge portions which do not appear in fig1 a but can be seen at 95 in fig1 b when the two circular elements 71 , 73 are superimposed . these edge portions 93 , 95 allow the edges of the flaps to be compliant to accommodate variations in the profile of the shaft of a surgical instrument especially when the instrument is being retracted . fig1 illustrates the positions of both petals 51 and flaps 83 and 91 ( shown as one item in fig1 ) during retraction of an instrument 96 from the seal assembly . located above armour layer 69 is upper clamp 97 which functions to hinder the inversion of armour layer 69 . as best seen in fig5 a and 5b , upper clamp 97 is a ring having an axial wall 99 extending between an upper , outwardly extending flange 101 and a relatively wider lower , outwardly extending flange 103 . flange 103 is provided with equally spaced apart hexagonal holes 105 to enable the upper clamp to be located on the pegs 47 . extending inwardly from axial wall 99 of clamp 97 are two diametrically opposed flats or ledges 100 which assist in preventing the armour layer inverting on withdrawal of an instrument from the seal assembly . each ledge 100 has a radial lower surface and a gently and smoothly inclined upper surface 102 , the latter facilitating the smooth entry of an instrument into the seal assembly . a flotation or bellows element 107 is located alongside upper clamp 97 . as best seen in fig6 and 8 , flotation element 107 is a ring of flexible elastomeric material which has a central portion 109 of serpentine configuration . the outer edge of the central portion 109 is provided with an enlarged head portion 111 which enables the flotation element 107 to be trapped between intermediate plate 37 and seal housing cap 113 . the inner edge of the central portion 109 is provided with a thickened tail portion which enables the flotation element to be fitted at this edge between the flanges 101 and 103 of upper clamp 97 . flotation element 107 allows an instrument inserted into to seal assembly to have a considerable degree of orbital movement ( radial float ) without loss of the gas pressure during an operation . the cannula 3 is assembled for use in the following manner . the stopcock lever 29 is inserted in the stopcock body 29 . the gasket 21 is inserted . the valve 33 is introduced into the housing 19 . the intermediate plate is then positioned on top of the valve . next the instrument seal member 51 is folded onto the lower clamp 43 . this process is illustrated in fig9 and 10a to 10e . fig9 shows the initial positioning of the seal member 51 on the lower clamp 69 with the petals in their unfolded positions . fig1 a shows the position after one petal 115 has been folded over so that the holes 65 locate on certain of the pegs 47 . then , previously adjacent petal 117 is folded over to reach the position illustrated in fig1 b and this is followed by the successive folding over of petals 119 , 121 and 123 , as illustrated in fig1 c to 10e . finally , petal 125 is folded over so that all petals are located on the pegs 47 . this is achieved by folding each petal , after the first petal , over the previously folded over petals and not by interleaving any petal with previously folded over petals . the result is a simple stacking of petals and this procedure avoids the need for a relatively difficult process of manoeuvring one or more petals to produce a woven configuration . each petal is in effect moved radially with respect to the lower clamp and this requires that three of the petals 115 , 117 and 119 each have a keyhole shaped hole which is located in a different position on the three petals so that the radial movement causes the keyhole shaped holes all to locate on key shaped peg 49 of lower clamp 43 . referring to fig4 and 15 of the accompanying drawings , items 43 , 51 , 69 , 97 and 107 together comprise a unit which is the seal core for the overall assembly . this unit may be used in other configurations of surgical access devices .
a surgical access device comprises a seal assembly having a plurality of part circular sealing members each attached to a common ring which is held within the device about its longitudinal axis . in use , the sealing members are located radially inwards of the ring in a stacked relationship . when not within the device , the sealing members are movable from a position radially outwards of the ring to a position radially inwards of the ring . a seal core comprises the seal assembly and a protective member which , in use , is located on the proximal side of the seal assembly . a method of assembling the surgical access device is also provided .