How can the presence of non-condensables in a refrigerant recovery cylinder be detected?

The presence of non-condensables in a refrigerant recovery cylinder can effectively be detected by comparing the cylinder pressure and temperature to a pressure-temperature (PT) chart relevant to the specific refrigerant in use. Refrigerants have defined pressure-temperature relationships, meaning that at a specific temperature, the pressure should fall within a certain range if only pure refrigerant is present.

If the measured pressure of the cylinder does not correspond to the expected pressure for the observed temperature, it indicates that non-condensables, such as air or moisture, may be present. Non-condensables do not condense at normal operating temperatures and therefore impact the pressure readings, diverting them from the expected values on the PT chart. This makes the PT chart a reliable tool for identifying the presence of non-condensables.

Other methods, such as checking the cylinder color or listening for sounds when shaking the cylinder, do not offer a precise or reliable means of verifying the purity of the refrigerant in the cylinder. Similarly, measuring the boiling point may not yield clear information about non-condensables since it is more affected by the mixture of refrigerants rather than solely indicating the presence of unwanted non-condensing gases.