mm,

since, you didn't provide very much info on your system's pressure and flow rate. The simple answer to your question is bigger is better because it reduces friction losses in the pipe. Friction loss equates to pressure loss over distance. There is a maximum flow that a certain size pipe can deliver(ask google). A larger pipe has a larger maximum flow rate which allows you to irrigate a larger area at one time minimizing your head/sprinkler/emitter count. Let us know the actual dimension of your beds (length x width) and how many. What is your source pipe size? Will you expand in the future? What is the 8 psi final pressure? Aloha

You size pipe for minimal pressure loss from friction from the water source to its destination. Pressure loss is determined by the type of pipe (old steel, smooth PVC) the length of the pipe and the rate of flow (gallons per minute). Elevation must be considered because you lose pressure going up hills and gain pressure going down hills.

A small pressure loss is normal and cannot be avoided. One must not try to cram too much water through a given pipe or the pressure losses will be large. Using too big a pipe doesn't hurt anything but you're buying capacity you don't need wasting your money.

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