A Thermodynamic Vent System (TVS) to vent a liquid hydrogen tank in low gravity was designed and built by Sundstrand. The TVS was designed and built to a General Dynamic Space Systems Division (GDSSD) specification and was based on earlier laboratory work and design studies done by GDSSD for NASA. The TVS assures that superheated vapor is vented from the tank to control tank pressure with minimum loss of fuel. Major components of the TVS are a swirl flow heat exchanger, an electric motor-driven mixer pump, a fully redundant electronic inverter, and a redundant combined regulator and shutoff valve. The TVS has been extensively tested; the test results compare well with analytical predictions. This paper will describe the system and discuss the test results.