I took a couple of (free) classes on pressure cookers at a local cooking supply store. What I was told was that any pressure cooker made since the late 70’s has 3 different levels of protection. My mother had a pressure cooker when she first got married, made pea soup in it, and had a fountain (it clogged the valve). She got one in 1973, used it for decades, and never a problem. She gave it to me, but when I found out it only had 2 levels of safety, I chose not to use it, because pressure cookers aren’t all that expensive. Besides, my slow cookers get similar results, so I generally put everything together in the morning so that it’s ready when I get home.