No, it is not possible to boil water in a pressure cooker without the lid on. The primary function of a pressure cooker is to create a sealed and pressurized environment by locking the lid in place. This pressure is what allows the temperature to rise above the boiling point of water, which results in faster cooking times.
Without the lid, the pressure cooker cannot build up pressure, and it functions like a regular pot. The lid is essential for trapping the steam generated from the boiling water, which increases the temperature inside the cooker. This elevated temperature and pressure are what contribute to the efficiency and speed of cooking in a pressure cooker.
If you try to boil water in a pressure cooker without the lid on, the steam will escape, and the water will simply boil at its normal boiling point, similar to any other open pot or saucepan. The lid is a crucial component of the pressure cooker's design and is necessary for the unique cooking process it offers.