I just pulled out an old Presto pressure cooker. This is probably over 20 years old. I don't even know if they make them like this anymore. The little knob in the lower left sits on top of the vent in the middle of the lid and acts as a pressure regulator. It says it maintains 15 psi while cooking. My goodness it's loud. You get the feeling that at any moment the hot contents of your cooker will burst free and go flying across the kitchen. It's probably why I abandoned it years ago.
So far I've made black beans, navy beans, chick peas, apples, and brown rice ... with varying degrees of success. The chick peas made a great hummus and the apple chunks made great applesauce but the black and navy beans I had to cook more after about 30 minutes in the cooker. I'm still experimenting... Does anyone out there regularly use a pressure cooker?