Why do potatoes cook faster in pressure cookers than in a normal vessel?

In a pressure cooker, the food is cooked at a higher temperature than in normal vessels. Pressure cookers are closed and air-sealed vessels that do not permit air or liquids to escape below a preset pressure. Upon heating, water evaporates inside the cooker and the steam pressure starts building up. The water then starts boiling at this higher pressure. This lets the potatoes cook faster. Pressure must be released before opening the cooker by letting it cool down or by opening a drain valve carefully.