The rupture disk (RD) safety circulating valve is the component of the DST toolstring, with the functions of both a safety valve and circulating valve. The RD safety circulating valve workes as a safety valve when the annulus pressure reaches a predetermined value. At that pressure, the valve isolates the workstring below the tool and establishes communication between the annulus and the workstring above the tool. The Rupture Disk Circulating Valve can be converted into a circulating valve when the ball valve section is removed and attach a lower adapter called RD Circulating Valve.
The valve can not be open when closed in downhole operation. RD Circulating valve is the same as RD Safety circulating valve except short of ball valve section, the annulus pressure made RD burst and the pressure goes into RD hole and push circulating mandrel forward, then open the circulating ports.