Speaking of Spare Ribs....
I often do spare ribs in my PC, not baby back but the big old slabs you used to get for $.79 lb I put a whole slab in and cook until tender then toss them on the grill -- I know rib affectionados are cringing --- but it's the way we've always done them. I have tried other methods, but I always return to the old standard.
Anyway back to my story, Last year I tossed a rather large slab of ribs in, added a little water and celery, onions, parsley and seasonings, got it up to pressure, set the timer for 20 minutes and walked away. About 10 minutes later I hear a big "WOOOOSH"! Dash into the kitchen and see everything is covered in rib juice --ceiling, walls, floor, counters. Apparently the ribs shifted and just managed to block the port in the center of the lid the weight sets on and the pressure relief valve did what it was supposed to.
In the 50 or 60 years my parents and I have been using PCs this is the first and only time we've had a problem, and to be honest it really was my fault. I'm just more careful now, but i still use it often.