Pressure Class Ratings
Pipe Fittings are commonly classified based on a pressure temperature rating system designated ASME. The ASME ratings are expressed in pounds such as #150, #300, #1000, #3000 and #6000.
Pressure ratings are dependent on the material used and the design of the fitting. Also the pressure that a fitting can accommodate fluctuates with changes in temperature.
It is important to note that the pound rating of a pipe system is measured by the part that has the lowest rating-the weakest link.
In conclusion, when you are purchasing piping components you should know the upper end of the temperature and pressure your system will need to accommodate. Also in terms of value, lower pressure fittings are in general less expensive than high pressure parts.