I have a valid single entry 30 day visa for China, which I plan to use in May.

However, in April I want to fly via Beijing and make use of the 72 hour free transit rule. Question: Will my visa that I have in my passport and that I will need in May, be used up with that entry or can I avail the 72 hour rule and still use my visa for my May stay later? In short, will my May visa remain untouched if I travel through Beijing for less than 72 hours stay in April?