Pressure cooker expandable gasket, how/why does it work?

[jes]

I am watching a cooking show (Chef At Home - Micheal Smith, my favorite) and he is talking about the technological advancements of pressure cookers. They don't explode every few weeks anymore because of an expandable gasket and sealable lid. I understand that a gasket is a piece of rubber or metal that allows a joint to be sealed but I don't understand how that can apply to a pressure cooker.

 

[Andy M.]

The gasket, usually rubber, sits between the lid and the top of the pan. The lid locks onto the pan and creates a pressurized seal.

 

[jes]

I see. So, it is around the rim of the pan to form a seal between the pan and the lid.

What would make it "expandable"?

 

[PrincessFiona60]

It is a very pliable gasket, it fills the space and can expand when needed. In cross section it resemble a tire, U-shaped, the open part is to the inside of the pan.

 

[Timothy]

I see. So, it is around the rim of the pan to form a seal between the pan and the lid.

What would make it "expandable"?

If the pressure in the pan gets high enough, it will blow the gasket out instead of blowing the pan lid off.

The flying lid and hot liquid are what are the danger. When the gasket blows, it allows the pressure to escape without harming anyone.

If that happens, the gasket should NEVER be reused. buy another one and install it on the pan.

 

[jes]

I understand. "Expandable Gasket" seems, to me, to be a bit misleading. It is just a gasket, the word expandable is just a confusing addition.

 

[PrincessFiona60]

The gasket does expand to fill the space, if it didn't you would lose pressure. This is important if you want to use a pressure cooker, it's the most important part to check and make sure it is in good shape before you attempt to use the pressure cooker.

 

[jes]

What causes the gasket to expand inward?

 

[PrincessFiona60]

It does not expand inward, it expands and open like spreading the arms of a U open, it fills the space with pliable rubber. Have you ever seen a pressure cooker?

 

[jes]

I don't think that I have seen any of the ones made in the last 20 years.

 

[Timothy]

I don't think that I have seen any of the ones made in the last 20 years.

They are quite different now, jes. The one I just bought about 6 months ago has 3 (Three) pressure relief valves.

 

[Andy M.]

We had a PC in the 70s. It had a rubber plug in a hole in the lid that would blow if the pressure got too high. It also had a rocker valve that regulated the pressure and would let excessive pressure bleed off. Finally, the gasket was designed to blow if pressure got too high. So even 40 years ago there were redundant safety systems.

 

[gadzooks]

I have three older stainless steel pressure cookers, all Presto. 3, 4 and 6 qt. Same gasket for all. It is, as PrincessFiona60 says, "U" shaped in profile, with the open face of the "U" facing inward. As the cooker pressurizes, it expands the gasket upward, downward and outward as far as the lip of the lid will permit, sealing the cooker. Most pressure cookers also have a safety relief that will blow if the cooker over-pressurizes. Else it could become a bomb.

 

[PrincessFiona60]

I have three older stainless steel pressure cookers, all Presto. 3, 4 and 6 qt. Same gasket for all. It is, as PrincessFiona60 says, "U" shaped in profile, with the open face of the "U" facing inward. As the cooker pressurizes, it expands the gasket upward, downward and outward as far as the lip of the lid will permit, sealing the cooker. Most pressure cookers also have a safety relief that will blow if the cooker over-pressurizes. Else it could become a bomb.

My new Fagor cooker has a much more supple and larger lid gasket. Works a charm, loved learning how to cook in the new cookers and a smaller one came with it so it's a bit more versatile.