The Tool Trap, normally situated above the BOP and below the lubricator stack, prevents the accidental loss of wireline tool strings downhole by use of a spring-loaded flapper that blocks the bore.
The flapper is designed to allow free operation of — and access to — the wire or cable but stops the passage of the tools from above.
When running into the well, the flapper is hydraulically held open until the tools have passed and then returned to the closed position during the wireline operation.
When pulling the string, the flapper automatically opens as the tool string strikes the closed flapper and the movement of the indicating lever gives a positive indication of the string position.
When the tool string is pulled fully through the Tool Trap, the flapper will automatically close to cover the well bore and prevent the string being dropped downhole.
The flapper can be manually opened without the use of hydraulics if preferred.