Optimal garden pressure irrigation system

Question

The garden has around 100 trees and some vine and the irrigation system needs at least 3-4 bars of pressure in order for the nozzles to spray water.

I made some drawings of 2 possible ways of connecting everything. The red line is the water coming from the pump through a 1 inch hose. Then it goes into a brass distributor, which has around 15 outputs of 1/4" each. From each output water flows through a thick tube that has 5.5mm diameter (the black lines with arrows). From the tube it goes into the nozzles for each plant.

First, where each group of plants is separated, and at the end of the line there is a plug, or the last nozzle can act like a plug.

Second, where groups are connected (no plugs)

The numbers of plants per group vary. On some lines I have 10 trees, on others 5, or 15 vines, etc. In both situations I will not be able to open all valves in the distributor because there is not enough water to irrigate all groups at the same time. So I would open just 1 group, then after 2-3 hours close and open another and so on..

What would be the optimal way of connecting everything, so I don't get any pressure drops at the ends?

Basically I want water on all nozzles to have the same pressure.

Right now, my setup is close to the 2nd drawing, but instead of a small distributor I have a long 1 inch pipe, and the issue is that pressure is lower at the edges then near the 1 inch pipe.

Answer 1

1/4" (6.3mm) tubing has gigantic friction losses. That is, loss of pressure when water is flowing that increases with length. 5.5mm tubing is going to be worse.

Given the scale implied by trees this would be problematic with drip emitters, and is unlikely to work at all with spray emitters.

You'll need a great deal more larger diameter pipe and relatively short 5.5mm lines connected to those, if the sprayers use 5.5mm lines.

Right now, my setup is close to the 2nd drawing, but instead of a small distributor I have a long 1 inch pipe, and the issue is that pressure is lower at the edges then near the 1 inch pipe.

That is normal and expected, due to the friction loss in the small tubing. Run your 1 inch pipe as a manifold going to all the rows, so that each individual sprayer connects directly to it through a similar length of 5.5mm tubing and the uniformity of pressure will vastly improve.

Depending on the flow rate of the combined spray emitters, the sections of 1" pipe might need an even larger supply pipe to keep the pressure in them roughly equal, or you might need to run only one row at a time, one after the other (there are irrigation distributor valves designed to do that automatically, as it's a common enough problem.)

Drip emitters tend to waste less water and make system design simpler as they apply water more slowly, reducing flow rate, reducing dynamic head losses. But 100 trees fed on 5.5mm tubing from a central distribution point still won't work due to friction head losses in tiny tubing.

Answer 2

You will drive yourself crazy trying to get equal pressure on each nozzle.

The goal is to get the correct amount of water to each plant. Concentrate on flow rather than pressure.

The bottom drawing will result in closer pressure between nozzles, but again the goal is flow. To achieve this the nozzles should be adjustable. Adjust each for the amount of water you want to each plant for the amount of time the system is on. If the nozzles are not adjustable, you need to get adjustable nozzles, otherwise the system will be unbalanced no matter what you do.

In theory an irrigation system should be able to be set and forgotten about, but this is not the case. The flow and subsequent amount of water to each plant will need to be adjusted occasionally. How often depends on many factors. This is something you will need to learn by experience.