Rfid unmanned project

GUYS,
i have been thinking a lot of using RFID technology for a certain application and would definately use it as my final year diploma project if i would make it work but i have some doubts since i am new to radio frequency topic and won't be studying this till my last sem(so plz some questions will be of amateur level)

topic:UNMANNED PETROL PUMP USING RFID

now with basic information from net and from project guide i can interface my rfid to detect specific cards of certain values via programming(100rs=1 ltr petrol) i am pretty sure i would be able to interface the led and the rfid card reader to my specific microcontroller*(via rs232 or if not connecting through max 232) now that's the 1st level of my project

CONFUSION:SEE now,since i introduce an 100rs rfid card to the reader the lcd will display card accepted and liquid should be pored in,now here's the problem-----HOW do i configure my petrol pump to pump up specific amount of liquid for the amount deducted through rfid card (ex:- 100rs deducted - 200ml should pour in),what kind of pump should i be using so that i can program it and interface to the microcontroller accordingly(i asked a project guy he said sort of submarine pump???)i am so confused about this later part
ANY HELP WOULD BE SO MUCH APPRECIATED
HAS Any one done a project like this i need schematics for this or similar to this,
THANKYOU(sorry for being noob)