Double Flight transit

If your entire transit time within China, counted from your first scheduled arrival, until your last scheduled departure is less than 24 hours, you will be eligible for 24 hour visa free transit and you don't need a visa. Quite the contrary, if your entire transit time takes just a minute more than 24 hours, you will have to obtain a visa in advance. Please, keep in mind that US citizens are eligible for 10 year multiple entry visa, so this is much better option than applying for a transit visa that is basically of the same price.