Ralston Instruments QTVF-000B-2F-2F 

Shut-off valve - 1/4" Female NPT x 1/4" Female NPT with male QT test port, brass

Install between a pressure gauge and the process and isolate the process from the gauge to perform a calibration of the gauge. After completing the calibration open the valve and place the gauge on-line, all without blowing down the system.