When the boiler is operating at the constant pressure, that means the vapour pressure of the water is equalized with the overlying pressure of the surface maintaining the Vapour pressure of the water and the boiling point. As long as these two factor do not change, any heat added to the vessel will let the escaping molecules to go and that is the evaporation made under perfect efficiency because all heat input will be transferred to the steam.
Kapag walang nagbago sa dalawang paktor ng hindi nagbabagong pwersa, ang kahit anong init na idagdag sa lalagyan ay hahayaang tumakas ang mga molekyul na pilit lumalabas. Ang resultang ebaporasyon ay nagagawa ng may perpektong epektibidad dahil ang lahat ng init ay nalilipat sa singaw. a