I am setting up an irrigation system for my ranch and I have a hard time calculating the minimum pipe pressure requirements to reduce cost. I need to know the maximum pressure the pipe has to cope with. The pipe would transfer water from a high elevated pond (with enough water to feed the line constantly) to a barn down below. There is a 166 meter height difference between the inlet and outlet. I can easily calculate the upper bound pressure as 16.6 bars, however as I get it, the friction loss plays an important role too. The pipe's length is 1200 meters and made of polyethylene (Absolute roughness of 0.007). We need to open and close the faucet on the exit pint on demand (important) so the water head may reach the full height of 166 meters when the outlet is closed. The question is: do I have to order the 16.6 bar pipe or a lower grade pipe would do?