 For pressure cookers with a weight, the weight is placed over the steam vent pipe while steam is being emitted to ensure the air inside has escaped.The newer generation pressure cookers, which have no weights, automatically expel air from inside for several minutes before a coloured pop-up indicator pin rises to seal the lid airtight; pressure then builds in the now airtight cooker.If the pressure cooker is already hot or a stovetop pressure cooker is placed on a very strong heat source, such as induction on too high a setting, the lid can seal airtight too quickly before the air inside has been removed.