The Design of Pressure cookers

Pressure cookers are generally made of aluminum or stainless steel. The former may be stamped and buffed or anodized, but this metal is unsuitable for the dishwasher. Higher quality stainless steel pressure cookers are made with heavy, three-ply, or copper-clad bottoms (heat spreader) for uniform heating, since stainless steel has lower thermal conductivity. Most modern units are dishwasher safe, although some manufacturers may recommend washing by hand. Some pressure cookers have a non-stick interior.

In most models, a gasket or sealing ring forms a gas-tight seal which does not allow air or steam to escape between the pot and the lid; other more expensive models feature a metal-to-metal seal. Normally, the only way the steam can escape is through a regulator on the lid when the pressure has built up. If the regulator becomes blocked, a safety valve is provided as a backup escape route for steam. The simplest safety valve is a loose-fitting rubber plug in the lid, held in place by steam pressure. If the pressure exceeds design limits, the plug pops out of its seat.

To seal the gasket, some pressure cookers have a lid lock with flanges, similar to a bayonet-style lens mount, that works by placing the lid on the pot and twisting it about 30° to lock it in place. Contemporary designs of this style of cooker also have a pressure-activated interlock mechanism that prevents the lid from being removed while the cooker is pressurized.

Other cookers, particularly the larger types used for home canning, have oval, over-sized lids. With these, since the lid is larger than the opening in the top of the pressure cooker, one inserts the lid at an angle, then turns the lid to align it with pot opening. A spring arrangement straddles the top of the cooker and holds the lid in place. When cooking, the pressurized steam inside keeps the lid tightly in place, preventing accidental removal.

Because of the forces they have to withstand, pressure cookers are usually heavier than normal pots of similar size.