Butterfly valve is also called a flap valve, is a simple structure of the regulating valve, but also can be used for low pressure pipeline medium switch control.

蝶阀又叫翻板阀，是一种结构简单的调节阀，同时也可用于低压管道介质的开关控制。

youdao

Probably, but Semmelhack points out that the second slot (covered behind a flap) is dedicated to loading the operating system, making it a trivial task to quickly switch between kernels or get unbricked.

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