Forward circulation mode allows the tubing string to be displaced into the annulus by a lighter fluid creating a desired under-balance, or accurately spotting an acid pill. A check valve mechanism prevents back flow from the annulus.
The reverse circulation mode allows annular fluid to be pumped into the tubing string, and a check valve prevents back flow from the tubing. This mode has applications for auto-filling the string during run-in-hole with a ball valve as the tubing pressure test valve; and, as an emergency kill valve below the test valve. The first rupture disc cycle enables the tool’s function, and the second rupture disc cycle locks the tool for the remainder of the test.