as seen in fig3 when shear pin 86 breaks ring 94 remains stationary held in position by lower mandrel 38 with seat assembly 82 shifting downwardly effectively leaving surface 96 unsupported allowing for radial outward flaring of seating surface 84 as will be later explained this allows the ball 98 see fig2 to pass seating surface 84 a lateral port 100 allows fluid communication from central flowpath 56 into variable volume cavity 68 at a point adjacent collet heads 102 as seen in fig1 the collet heads 102 are trapped between tapered surface 104 on lower mandrel 38 and surface 106 on upper housing 24 the collet heads 102 are connected to collet ring 108 which is connected by thread 110 to split nut 112 split nut 112 is slidably mounted to surface 114 of compensating piston 116 seals 118 and 120 are mounted to the compensating piston 116 seal 120 seals between compensating piston 116 and housing 26 while seal 118 seals between compensating piston 116 and lower mandrel 38 compensating piston 116 is movable within variable volume cavity 68 for reasons which will be described below bottom connector sub 40 acts as a travel stop for compensating piston 116 as shown in fig3 thread 122 secures bottom connecting sub 40 to lower mandrel 38 set screw 124 secures the threaded connection 122 and.