An apparatus for controlling flow in a fluid flow path can include a chamber containing an expandable material, the expandable material being configured to expand out of the chamber into a portion of the fluid flow path so as to at least partially block the fluid flow path. The apparatus also can include at least one structure providing flow communication between the chamber and the fluid flow path. The at least one structure can be configured to pass the expandable material from the chamber to the portion of the fluid flow path during expansion so as to control a rate at which the expandable material expands into the portion of the fluid flow path.
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