“气垫”对于我们并不陌生。我们做一个小实验:在高压锅里装些水,扣上限压阀,用手旋转这阀,却旋转不起来,因为阀与锅盖之间的摩擦力很大;点火烧高压锅,一会儿冒出水蒸汽将阀抬起,这时你再轻轻旋转,瞧啊!限压阀在锅上旋转个不停!原来,水蒸汽在限压阀与锅盖之间形成的“气垫”使 “Air cushion” is no stranger to us. We do a little experiment: in the pressure cooker with some water, buckle pressure limiting valve, hand rotating the valve, but can not spin because of the friction between the valve and the lid is very large; ignition pressure cooker, and then emerge Steam will lift the valve, then you gently rotate, look ah! Pressure limiting valve in the pot rotation non-stop! The original, water vapor pressure limit valve and the lid formed between the “air cushion” so that