The ingenious design of the inner lid pressure cooker

Have you ever used an “inner lid” pressure cooker? Looks like this:

Someone who has never used one before might be super confused on how the lid needs to be secured. What seemingly looks like a lid that cannot fit surprisingly fits snugly thanks to the properties of an ellipse.

Lids generally go over the opening and have a clear border that we are used to. Inner lids on the other hand are strange at first because the lid goes into the cooker and sits snug below the lip of the cooker body!

Standard cooker that close from the top are fighting the pressure that builds from steam inside. They are holding onto the lip of the cooker body for dear life under very high pressure. There is usually a rubber gasket between the lid and the cooker body that creates the seal. Over time the pressure, stress and general ageing leads to leaks and loss of pressure.

Now for the ingenious part, once the pressure builds inside an inner lid cooker, The pressure is actively pushing the lid onto the lip of the main body. So higher the pressure, better the seal! The lid is no longer fighting for its life, Its just hanging out there while the cookers own pressure does the work of maintaining the seal. These cookers too have a rubber gasket but its usually much smaller and usually look like a O-ring that has been stretched out.

Flush tanks use a similar mechanism too. When you press the button/lever, the valve is actually being lifted! once the valve is released by the flush mechanism, water itself actually pushes the valve down effectively sealing it until its lifted up again.

Engineering at its best. Instead of fighting something you want to contain, use it!