I have had my pressure cookers for 35 years, and they are as safe as the one I bought last year. They are Presto cookers. I cannot take the top off before the pressure is released--maybe a very strong person could, but it would take a great deal of effort. (I know the new ones have an interlock thingie that drops to release the lid when the pressure falls, but the amount of strength it would take to turn the lid on mine when the pressure is high is incredible.)
Read the manual, follow the directions. If it is old, check the gasket--it should be flexible. If it is not, or if it shows any cracking, buy a new one. The other thing that might need to be replaced is the safety release--it is a small bolt on the underside of the lid, with either rubber or metal showing thru on the top of the cooker. If pressure/temperature gets too high, that plug will melt and you will have stuff sprayed allllllll over the ceiling. But the cooker itself will not explode!! I am very careful not to put my face over the cooker while it is cooking, just in case that safety plug goes!
I had one blow once--before it happened, I noticed that a tiny amount of water was bubbling out of the plug. Now I replace them every 5 years or so, just to make sure. I do a lot of canning, so you might never have to replace yours.
Mine have the weight that goes on top and jiggles, and I have had no problem putting it in the sink and running water over it to cool it down. I put some water in the sink, and run cold water over the top. I have never accidentally knocked the weight off.
I just haven't been the same
since that house fell on my sister.