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What does "saturated temperature" and "saturation pressure" mean?

Saturation Temperature; you see it written in equipment manuals, hear it mentioned during training seminars, and secretly hope no one asks you what it is. Go on, admit it, you don't know what the heck saturated suction pressure really is. Don't feel bad, most technicians don't, but now you're going to.

First; anything that can boil or condense has a saturation pressure and temperature: water gasoline, alcohol, and refrigerants, just to name a few.

So, what is saturated temperature and saturation pressure? It's the temperature and pressure where something begins to boil but is also a liquid. Let's use water as an example-

70 degree water at sea level is a liquid. Heat the water to 212 degrees and it begins to boil; there's liquid (water) and gas (steam). This is the saturation temperature of water at atmospheric pressure.

But, if we reduce the pressure on the water the boiling temperature drops. This is why water boils at a lower temperature in the mountains- the pressure on the water is lower.

If you increase the pressure on the water the boiling temperature increases, like in a car's radiator. The reason a car's coolant can be 220 degrees and not boil is because its under 15 psi of pressure; at 15 psi the boiling point of water is now 250 degrees.

How do you find the saturation temperature for a refrigerant? Easy; look at your pressure temperature chart. If you don't have a temperature pressure chart look at the temperature bands on your refrigeration gage set; each band is for a specific refrigerant.

So, in a nut shell; saturation temperature is the point where something is at its boiling point but exists in a liquid and gas state.

Saturation pressure is the pressure required to keep something in a liquid and gas state at a certain temperature.