I use my pressure cooker often and love the delicious food it makes for me.
For your pot roast and vegetables:
heat the stove top pressure cooker over medium with a little oil in it; brown your pot roast well on all sides; add liquid (beef broth or water) according to your cooker's directions - mine has 2 cups of liquid for 3 lbs. of pot roast; add salt, pepper, chopped onion, bay leaf; put lid on pot and cover securely; place pressure regulator on the vent pipe (if your make uses the "jiggler" regulator); over medium high heat, bring pressure up so regulator starts to rock, then lower heat to maintain rocking action and to maintain correct pressure for cooking; cook roast 30 minutes; turn off heat - then take pot to sink and let a small stream of water run over the lid of the pot and down the sides to completely decrease the pressure.
Carefully take off lid when all pressure is gone. Add in potatoes, quartered, and carrots in large chunks. Put pot back on stove, put lid on, put pressure regulator on and bring up pressure again. Lower heat to maintain pressure and cook 15 minutes. Then once again do rapid release of pressure under gently running water in sink.
The new generation of pressure cookers are very much safer and easier to use than the older generation. I have a 4 qt. stainless steel Presto that was about $50. I really like using it, but if I had it to do over, I would have bought a 6 qt. pot. Fagor is a good brand and there are other really good brands.
Lots of people love the electric digital pressure cookers, but there is more that can go wrong with them. I prefer the low tech model for myself and have been very pleased with the use of it. I love to make country style pork ribs with sauerkraut, potatoes, carrots and onions in apple juice or apple cider. Beans are done in 15-30 minutes, brown rice in 10-12 minutes, ribs and sauerkraut in 15 minutes, chili with meat in 5 minutes.
A stainless steel model is the best, read reviews on the brand/model you are considering, read all you can about the use of pressure cookers before you buy!
This website is a wonderful resource:
www.missvickie.com/