Hansen H8021, 1/2 (13MM)3-Way Dual Shut-off Valve, 1/2 FPT Connection.

These rugged, forged steel bodied valves facilitate the parallel installation of pressure-relief valves. Because three-way  valves  will  not  isolate  both  pressure-relief  valves  simultaneously,  they  are  considered  the  only  acceptable type of shut-off valve for use with refrigerant relief piping. Their durable metal-to-metal seating and patented non-leak packing plus o-ring stem seal design combine for long, trouble-free service. Inlet and outlet connections are threaded female NPT all the same size. SW and BW connections are also available.

The valve stem should be positioned so that only one pressure-relief valve is activated. While the valve can be either frontseated (front port is closed) or backseated (back port is closed), the backseated position (shown) is recommended for normal use because it takes pressure off the packing and reduces the possibility of packing leaks