Work Compressor

i want to build a portable gas powered air compressor ( i have already buildt a 60g 110v air compressor for home that works just fine no problems). on regular compressor you plug them inick,turn on the switch and thats it. compressor starts shuts off at regulated psi. while using compressor, pump and starter cuts in at regulated psi. by itself repetes over to keep regulated psi in tank. well if tou have to pull a draw string to start a gas powered compressor and it starts compressing air. what happens when it reaches desired psi or when pressure drops and has to fill up again. do i have to manually start this thing every timepsi gets psi gets low ? or how does it start again without me having to manualy start it? or does it stay running all the time? do i need any special or different valves or something? or just HOW DOES IT WORK?