If I'm applying for an S1 visa, how many enteries and exits out of the country am I granted?

I'm a student and I'm planning to get my Chinese one in Hong Kong. After getting it, I'll have to come back to China to resume my studying. I have to leave China for school trips after getting my S1 type and I want to know how many times I can exist and enter the country with my Chinese one. I will be having multiple school trips in and out of China so how can I work this out?