So many people are doing gravity feed systems we put together some kits just for this application.
A couple things to keep in mind. first, you still need to have filtration which we have included. Second, is a number you need to write down and it is .433. That is the amount of PSI you get for each foot in elevation the water supply is above the drip system.
The systems need at least 15 PSI. This means your water source needs to be 35 ft above your drip system. formula is .433 X 35 = 15.155 PSI
The alternative is to use a pump to get the pressure, but the news on this is not good.
Currently we cannot recommend any pump as there are no pumps that support the specs needed for a drip system. This has been an issue for many years now and none of the pump companies seem to be willing to make one. Some customers have used pond pumps but these will burn up over time, how much time we do not know. Sorry, but that is all we can tell you on pumps.
Also be aware that because of the low PSI of a gravity feed system our automated valves will not work. But lets face it you are going low tech by doing gravity so then asking to add high tech to it is well......................counter intuitive shall we say :-)