Patent ID: 8636073

Claim:
A well tool apparatus, comprising: a tubular housing having upper and lower ends for coupling into a pipe string extending into a well, the housing having an axially extending bore, the bore having an enlarged diameter portion; a drop member seat assembly in the bore in a first position above the enlarged diameter portion for receiving a drop member conveyed down the pipe string, the seat assembly having a passage therethrough that is blocked by the drop member after the drop member lands on the seat assembly; a retainer that retains the seat assembly in the bore above the enlarged diameter portion, the retainer allowing the seat assembly to move downward from the first position to a second position in the enlarged diameter portion in response to a selected fluid pressure applied in the bore above the seat assembly after the drop member has landed on the seat assembly; the seat assembly being radially expansible to an expanded position while in the enlarged diameter portion so as to enlarge a diameter of the passage sufficiently to allow the drop member to pass through the passage; and an annular spring in the bore and cooperatively with the seat assembly to urge the seat assembly to the expanded position.