Transit permit for US Citizen to Shanghai

I am flying through Hong Kong to Shanghai On August 3rd and flying out of Shanghai on August 6th. I will be in China for less than 72 hours. My flight originates in Tel Aviv and takes me through the US then to China and then back to Tel Aviv. I am a US Citizen. Do I need to apply for a visa or can I rely of the 72 hour free transit.

Thanks - Ari