in the drawings , like numerals indicate like elements throughout . certain terminology is used herein for convenience only and is not to be taken as a limitation on the present invention . the terms “ distal ” and “ proximal ” refer , respectively , to directions closer to and away from the vascular insertion site on the patient . the terminology includes the words specifically mentioned , derivatives thereof and words of similar import . the embodiments illustrated below are not intended to be exhaustive or to limit the invention to the precise form disclosed . these embodiments are chosen and described to best explain the principle of the invention and its application and practical use and to enable others skilled in the art to best utilize the invention . in prior art fig1 and 2 , a sheath assembly 10 is shown comprising a dilator 12 and a sheath 14 , and having a longitudinal axis “ l ”. dilator 12 has a dilator hub 16 at its proximal end , and its distal end portion 18 extends beyond the distal end 20 of sheath 14 to a distal tip 22 . sheath 14 includes a sheath tube 24 and a sheath hub 26 at the proximal end of the sheath tube , and is seen in fig2 with the dilator removed . sheath hub 26 is seen to have grippable wings 28 to facilitate the initiation of splitting by the practitioner to peel away the sheath from an inserted catheter ( not shown ). to facilitate splitting of the sheath 14 from around the catheter , the sheath tube has a pair of opposed frangible seams 30 , and sheath hub 26 includes frangible webs along opposed gaps 32 that are aligned with seams 30 . the proximal end 34 of sheath 14 includes a threaded locking arrangement for locking with the dilator hub 12 prior to removal of the dilator . sheath assembly 100 of the present invention is illustrated in fig3 and 4 . the sheath assembly includes a sheath tube 102 with a proximal end portion 104 and extending to a distal end , with a passageway extending therebetween defining a longitudinal axis . the sheath tube 102 preferably is extruded of polytetrafluoroethylene ( ptfe ) having longitudinal polymeric orientation providing inherent lines of weakness represented as lines 106 , for splitting therealong once splitting is initiated at the hub seams by the practitioner after completion of the insertion of the catheter &# 39 ; s distal portion into the vasculature of a patient ( not shown ). alternatively , as is shown in prior art fig1 and 2 , the sheath hub can having a conventional pair of opposed seams or frangible sections 106 that define weaknesses along which the sheath tube is easily split by the practitioner . referring primarily first to fig3 , a sheath hub 110 is affixed to the proximal end portion 104 of the sheath tube , the sheath hub being affixed to the sheath tube along the distal end portion 112 of the hub . a pair of wings or tabs 114 extend from respective opposed sections 116 , 118 of hub 110 at its proximal end 120 , for gripping by the practitioner for initiating the splitting of the sheath assembly for tearing it away from the catheter , by their being pried toward the sheath distal end such that the splitting of the hub begins at its proximal end 120 and separating hub sections 116 , 118 completely from each other along a pair of opposed gaps 122 . a dilator 200 is disposed through the sheath with its proximal end portion 202 extending proximally from the sheath hub 110 and including a dilator hub 212 . also seen in fig3 is a frangible section 124 disposed along the inside edge of gap 122 of sheath hub 110 ; the frangible section or webs on both sides of the hub join together the two hub sections 116 , 118 . now referring to fig4 , valve 150 is shown exploded from hub 110 , the two halves 182 of cap 180 are shown exploded from hub 110 and valve 150 , and dilator hub 212 is withdrawn from the sheath enabling showing of the dilator &# 39 ; s elongate tube 204 and clearly showing detail of the cap 180 and valve 150 . hub 110 includes a large diameter cylindrical portion 126 extending to its proximal end 120 and to a smaller diameter distal end portion 112 whereat it is affixed to a proximal end of sheath tube 102 . a passageway extends through the hub 110 in fluid communication with the elongate passageway of the sheath tube 102 . proximal end 120 of hub 110 includes a proximally extending wall 128 defining therewithin a valve - receiving recess 130 having extended lateral recess portions 132 to either side of the passageway 126 . extending proximally from the recess bottom in each lateral recess portion 132 is an anchor post 136 that is generally centered with respect to the respective lateral recess portion 132 and is associated with a respective valve half . shown just laterally outwardly of the opposite ends of wall 128 are a pair of apertures 138 for securing the cap to the hub 110 , discussed later . hemostasis valve 150 will now be described with reference to fig4 to 7 . valve 150 includes opposing halves or portions 152 a , 152 b that preferably are heat - fused together along a weak but sealed interfacial joint 154 ; alternatively , the opposing halves 152 a , 152 b can be bonded with a weak silicone adhesive . at its distal end , valve 150 includes a transverse distal section 156 . distal section 156 includes a slit 158 therethrough extending partially to the peripheral portions thereof . valve 150 also includes a proximal cavity 160 for receipt of the distal end of a dilator or catheter and may include an annular ridge 162 for engaging the side surfaces of the device inserted thereinto . each valve portion 152 a , 152 b includes a lateral flange or ear 164 a , 164 b at its proximal end , which further includes a post - receiving aperture 166 a , 166 b therethrough ; preferably , a thick flange extends from the lateral flanges to surround the entrance to proximal cavity 160 . the valve 150 may be initially molded in two separate sections or halves , or , as is preferable , initially molded as an integral whole that is bisected into opposing halves . the valve halves 152 a , 152 b may be made of silicone and may be fused together by a weak but sealed interfacial joint 154 such as by placing the valve halves into a common conforming mold of the shape of an integral valve body and maintained at 400 ° f . for 1 . 25 hours . optionally , an additional slit 168 can be formed through transverse distal valve section 156 partially along the weak interfacial joint 154 , thus being orthogonal to slit 158 . referring now to fig4 , cap 180 preferably comprises two completely separate but identical halves 182 , for securing valve 150 within valve - receiving recess 130 of sheath hub 110 . the interface 184 between the cap halves 182 is aligned with gaps 122 of hub 110 and seams 108 of sheath tube . cap 180 defines a passageway 186 extending therethrough from a beveled lead - in at the cap &# 39 ; s proximal end , with passageway 186 sufficiently large in inner diameter for a dilator and a catheter to be movably inserted therethrough . an outer cap wall 188 extends distally to be received around wall 128 surrounding valve - receiving recess 130 of hub 110 , and securing posts 190 of the cap halves are snap - fitted and / or friction fitted into apertures 138 of hub 110 ; optionally , each cap half may also be affixed to a respective hub half - portion by adhesive . also , optionally , the cap halves 182 may include respective protuberances and apertures along their interface 184 for precise co - alignment when assembled paired together to the hub 110 . cap 180 may include a locking section for lockingly engaging the dilator hub 202 of the dilator 200 . the locking section is shown to comprise a pair of locking pins 192 extending proximally from a proximal surfaces of the respective cap halves , each locking pin 192 including an enlarged head 194 on the end of a pin shaft 196 . a distal end 206 of the dilator hub 202 includes a cooperating locking section adapted to grip the locking pins to secure the dilator in position assembled to the introducer sheath assembly 100 . the cooperating locking section is shown to comprise a pair of hooks 208 that extend first radially outwardly from the side of the dilator hub distal end 204 and then circumferentially a selected small distance in a common direction , thus defining a pair of post - receiving slots 210 that are each sufficiently large to receive in a snug fit thereinto the shafts 196 of the cap &# 39 ; s posts 192 distally of their enlarged heads when the dilator 200 is fully inserted into the sheath assembly and abutting the cap , and then rotated a small angular distance in the common direction thus moving the hooks about the locking pins . the interrelationship of the various associated portions of the hub , valve and cap is best explained with respect to fig3 and 4 . valve 150 is seated within valve - receiving recess 130 of sheath hub 110 . the anchor posts 136 of the hub 110 extending through the apertures 166 a , 166 b of the valve ears assures that the valve halves will become separated from each other and remain with the respective hub portions when the hub is split for peeling the sheath assembly from about the catheter after catheter insertion . similarly , the respective cap halves 182 will also remain with the respective hub portions upon splitting of the sheath hub 110 . frangible sections or webs 124 of hub 110 that join hub sections 116 , 118 are formed adjacent the inside surface of the passageway of the hub and are very thin . it is preferred that , mainly for manufacturing reasons , the gaps 122 of hub 110 extend radially inwardly from hub outer surfaces to inner gap end portions that are u - shaped converging at the frangible webs 124 , in order for the mold inserts to remain relatively thick , robust and durable over many molding cycles and also to carefully control the thickness of the frangible webs . the webs may have a thickness , for example , of about 0 . 005 in ( 0 . 127 mm ), and the width of the gaps 122 at the outer surfaces can be , for example , about 0 . 010 in ( 0 . 254 mm ). it can be discerned from fig6 that the transverse distal section 156 of the valve would be abutted by a proximal end of a guide wire ( not shown ) during initial placement of the sheath assembly over the guide wire after the guide wire is placed in the vasculature , later by the dilator distal tip inserted through the hub and valve and later by the catheter distal tip , with the slit 158 permitting an opening therethrough in response to guide wire , dilator or catheter insertion , with the valve maintaining engagement with the outer surfaces of the guide wire , dilator or catheter as it passes therethrough ; and the slit will also close against the guide wire upon withdrawal of the dilator from the sheath assembly , forming a hemostasis seal and preventing effusion of blood . the hub and the cap may be made of polyethylene or polypropylene . an enlarged cross - section of the proximal end of the assembly 100 , 200 is depicted in fig8 , wherein the sheath hub 110 contains the split hemostasis valve 150 seated therewithin , the cap half members 182 , 182 and the dilator 200 locked to the cap half members so that the dilator tube 202 extends through the valve 150 and into the sheath tube 102 . the half portions of valve 150 are secured in place by posts 136 extending proximally through apertures 166 a , 166 b . cap posts 190 are fitted into holes in the hub half portions . dilator hub 204 is secured to cap members 182 when hooks 208 are rotated and post - receiving slots 210 thereof are snap - fitted around locking pins 192 of the cap members . an opening 220 in the proximal portion of dilator hub 204 permits insertion therethrough of a guidewire ( not shown ). a view of the entire assembly is shown in fig9 , partly in cross - section to show another embodiment of valve 250 in its open state , with a valve 250 and a valve half 252 illustrated in fig1 and 11 , respectively . two or more rib portions 268 are provided along outer surfaces of the converging distal end portions 270 of the valve halves 252 to enhance the closing of slit 258 either entirely , if no medical device extends therethrough , or tightly around a medical device extending therethrough , by virtue of the stiffness of the added material . it will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof . it is understood , therefore , that this invention is not limited to the particular embodiments disclosed , but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims .
a tearaway sheath assembly having a splittable sheath tube a splittable hub , a split valve and a split cap . the valve has a slit at least partially across the transverse distal section such that transverse distal section may be displaced laterally during insertion through the slit , of a dilator or a catheter . the valve is formed in two separate halves that are fused or adhered to each other to form a sealed weak bond that is easily broken during splitting of the sheath ; each valve half is mechanically affixed in a proximal valve - receiving recess of the hub such as by anchor posts extending through apertures in ears of each valve half . a two - part cap is affixed to the hub proximal end and traps the valve between itself and the hub . pairs of opposed gaps of the cap and the hub are aligned with lines of weakness or seams of the sheath tube and the weak bond of the valve , facilitating splitting of the assembly when desired by the practitioner to peel it away from the inserted catheter .