SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

Heads use water, at a certain gpm, and the total gpm number is used to calculate pressure losses through pipe and valves.

irrigationtutorials.com

It's not a question of pressure drop at the head. It's a question of do you have enough pressure left by the time the water reaches the heads.

Wet Boots has it right, you need to read the materials available at www.irrigationtutorials.com.

But the basic idea is you start with your static water pressure, subtract off all of the expected pressure losses, and the resulting value is the working pressure of the heads. The specifications of the heads will tell you what pressure ranges it can operate at and what it's performance (usually in the way of water radius and gpm) will be a various working pressures.

So usually, one of the ways to work it is to assume an expected working pressure at the heads (say 40psi). You look at the specs of the sprinkler heads and determine what their gpm flow rate is going to be at that pressure. You then use those flow rates to determine your pressure losses in the meter, filter, backflow, valves and pipe. If your static water pressure minus all these calculated pressure losses is less than the assumed 40psi working pressure at the head, then the head will not perform as designed. You will have to find ways to reduce your pressure losses (larger pipe and lower total gpm by using fewer heads per zone).