60 not shown flows down the tubing string and seats against the seat segments 62 and elastomeric members 64 that compose the expandable seat 52 in this manner the ball 60 engages with and seals against the expandable seat 52 to substantially prevent fluid flow through the expandable seat 52 and connected inner sleeve 54 causing an increase in pressure applied to the ball 60 and sleeve assembly 50 relative to the pressure below the sleeve assembly 50 when this pressure differential is sufficient to cause the sleeve assembly 50 to exert a shearing force on the port inserts 32 greater than the shear strength of the shear joints 47 the force exerted by the expandable seat 52 separates the shearable portions 46 of the port inserts 42 and releases the sleeve assembly 50 the pressure differential causes downward movement of the sleeve assembly 50 with the ball 60 engaged to the expandable seat 52 to the second position shown in fig3 as shown in fig3 and 4 the insert sleeve 54 is impeded from further downwell movement once in contact with the lower annular shoulder 58 after moving to the second position the ball 60 is impeded from further downwell movement and initially remains engaged with the expandable seat 52 which is in an unstressed state the ratchet ring 59 engages with the locking section 57 to prevent upwell movement of the sleeve assembly 50 as a result of the shearing the channels 48 of the port inserts 42 provide fluid communication paths to the exterior of the housing 22 in this u201c opened u201d state fracing may commence through the channels 48 flow of fracing material at normal fracing velocities causes erosion of the port inserts 42 and increases the diameter of the channels 48 as shown in.