A Cryo gas is a gas which is gaseous at ambient temperature and pressure and becomes liquid because of cooling and compression. Due to cooling and compression the volume of the gas can be reduced and thus it’s possible to store a huge quantity inside a vessel. Typical liquid gases which are stored in closed vessels are nitrogen, oxygen, argon, carbon dioxide, liquefied natural gas (LNG) and nitrous oxide. The following chart shows the boiling point of these gases at ambient pressure and at 20 bar inside the vessel: Ambient pressure 20 bar nitrogen -196°C -157°C oxygen -183°C -140°C argon -186°C -143°C carbon dioxide Not liquid -19°C liquefied natural gas -162°C -107°C nitrous oxide -88°C -16°C The lowest temperature for liquid technical gases inside a vessel is -196°C of the liquid phase of nitrogen, if there is about 1 bar inside the vessel. If the temperature of the liquid gas inside the vessel increases, then the pressure inside the vessel increases as well. A vessel for liquid gases always consists of two vessels: one inner vessel and one outer vessel. There is a vacuum between the vessels which are connected by steel rods. The vacuum isolates the inner vessel from the outside temperature to ensure that the temperature of the medium inside the vessel is less influenced by the ambient temperature. There are two pipes which connect the inner vessel with the pressure gauge mounted outside the vessel. One connects the upper part of the vessel (gaseous phase) with the pressure gauge and the other connects the lower part of the vessel (liquid phase) with the pressure gauge. As soon as the gas in the pipe leaves the outer vessel, that is the isolated area, it will become gaseous. Within the pipe, the medium will reach the ambient temperature before it reaches the gauge. As a consequence, the lowest medium temperature in the pipe outside the vessel is the ambient temperature. For our Cryo Gauges the lowest permissible ambient temperature is -40°C. The medium is always gaseous when it reaches the pressure gauge.