The Difference Between a P/T Chart & T/P Chart

Why is the Liquid (Bubble) number greater?than the?Vapor (Dew)?number on a Temperature versus Pressure chart, while being lower?on a Pressure versus Temperature chart? ?

Use the picture below for this example. If you follow the orange line, which represents the measurements for a T/P chart, you will notice that R454B at 45°F will have a Liquid (Bubble) measurement of 124.6psig and a Vapor (Dew) measurement of 118.8psig. These measurements represent the points of pressure achieved to satisfy saturation of the refrigerant at the Liquid state and the Vapor state. If you follow the white line, which represents the measurements for a P/T chart, you will notice that R454B at 112psig will have a Liquid (Bubble) measurement of 43.9°F and a Vapor (Dew) measurement of 46.3°F. These measurements represent the points of temperature achieved to satisfy saturation of the refrigerant at the Liquid state and the Vapor state. It is important to understand the relationship of refrigerants with the use of either a Temperature VS Pressure chart, or?a Pressure VS Temperature chart. ?

Here is another way to visualize the two charts:

Click on the T/P chart below for a FREE digital download of our comparative T/P chart.