Rice cookers are not sealed for high pressure (they are in fact not sealed at all, just like regular pots and lids, because they need to lose excess moisture) and they are configured for this one particular thing: every rice cooker is calibrated for a fixed serving of rice (or couple different settings) with fixed amount of water. All it really does is turn off at the perfect moment, which is determines by weight. which is determined by a thermostat (magnet-based in this case)