Charge Factor

A vessel must have space for vapor as well as liquid. As the temperature rises, the liquid expands. The vapor-filled space becomes smaller. At a certain point, there will only be liquid in the vessel. Beyond this, even a slight increase in temperature causes great pressure to build up in the vessel as the liquid attempts to continue expanding despite the absence of the necessary space. The forces that result are strong enough to rupture the vessel. To prevent a vessel from being overfilled, the regulations regarding compresses gasses specify how many kilograms of refrigerant that may be added to a vessel per liter of interior volume. Multiplying this filling factor with the interior volume gives the permitted filling capacity. The figure for refrigerant used in vehicles is 1.15 kg/liter.