"GMasterman" wrote in message
...
As I remember, my Mom's old pressure cooker had just an open tube on top
that
served as a safety when a calibrated weight was set on top. As pressure
biult
uo, the weight, which sorta looked like a solid metal jigger, would lift
and
vent the excess steam. Bet it would not build more than a pound or two

On my Presto 4 qt pc the 'jigger' serves as a crude pressure regulator.
IIRC the standard operating pressure is about 15 psi that raises the boiling
point of water to about 250 degF. More sophisticated cookers will allow you
to choose several operating pressures(i.g. 8,10 psi). My cooker has a 'blow
out' rubber assembly on the lid in case things go bad. I have two of these
cookers and use one of them nearly every day for fat-free cooking of my
meat and taters.

Larry