What is Pressure sealed cooling in engine?

  The boiling point of water is raised at higher pressure, with consequent reduction in coolant and the radiator weights and greater thermal efficiency of the engine due to higher operating temperatures. For approximately 10kN/m² increase in pressure, the boiling point is raised by 2.5^oC.  A radiator cap is used to achieve this special pressure-sealed. The pressure blow-off valve opens when the pressure in the system exceeds a certain predetermined value, say 50kN/m². A vacuum valve is provided to safeguard against the radiator collapse due to vacuum if the steam inside suddenly condenses to form a vacuum.

          When the cooling water cools down, its volume decreases and cooling water in the reservoir returns to the radiator, the reservoir is usually made of translucent plastic so that it can indicate the level of the coolant anytime.

              An additional advantage of this system is that being sealed there is no loss of coolant and thus it is very much suited in deserts. Further, the cooling efficiency of the system is not decreased at high altitudes where due to low temperature and pressure, the boiling point is otherwise low.

          An important precaution, however, has to be observed in case of pressure-sealed cooling, while checking the coolant level. The pressure cap should, initially, be opened only slightly, just sufficient to release steam and pressure. Only after the complete release, the cap should be opened fully.