Why do some pressure cookers initially leak Why do some pressure cookers initially leak steam from the sides and after a while settle down and don't leak? Is it a positive feedback mechanism from the building steam which makes the sealing tighter and vice versa?
 A: An answer to v1 of the question (that didn't emphasize the sides):
According to this cooking website, the pressure cooker valves are designed to be naturally "open." As the water heats up, the pressure inside will be slightly higher than outside (which is why you see steam escaping). At some point the valve is designed to "close" once a certain minimum internal pressure is attained.
Directly from the website:

A spring-loaded valve is normally open so that air can escape. As heating begins, expanding vapor pushes this valve up, closing off the vent. (At very high pressures, it rises farther and reopens the vent to release excess steam.) The valve regulates the pressure inside the cooker to a preset level: typically 0.7 or 1 bar / 10 or 15 psi above atmospheric pressure; this value is called the gauge pressure.

As for why one would choose to have this feature, that's a separate engineering question in my opinion. One advantage, though, is that it might make cleaning easier so you don't have a sealed off area getting nasty when not in use. Additionally (and probably more importantly), the same valve mechanism can be used to control whether it is safe to open the pot or not; an open valve (with little to no gauge pressure in the pot) is safer to open than a closed one.
