What Happens When Water Reaches a Sprinkler Head?

It is important to see how hydraulic principles apply to a landscape irrigation system. To better understand how a typical system works, let's look at a sprinkler system that has four sprinklers using 10 GPM each for a total of 40 GPM. The system has 30 PSI at the control valve and has been installed as shown in Fig. 22.

When the system is in operation, 10 GPM flows from each sprinkler head. The pressure at each sprinkler remains relatively constant because the pipe and fittings have been sized to minimize pressure loss. For the sake of this example we will assume a negligible pressure loss so that each sprinkler is operating at 30 PSI. Later we will examine the pressure losses between each head.

At point A (below sprinkler No. 1) in Fig. 23 (above), the flow of water splits, with 10 GPM flowing up and out of sprinkler No. 1 and 30 GPM flowing on to sprinkler No. 2. The pressure, however, does not split. Instead, the pressure is equal in both directions at point A. The same principle applies at each subsequent split in the line.

The flow of water splits in the same way it did at point A with 10 GPM flowing to the sprinkler and 20 GPM flowing toward sprinklers farther down the line. Once again, the pressure does not split. The pressure at point B (below sprinkler No. 2) is 30 PSI both at the base of the sprinkler as well as in the direction of the sprinklers downstream.

Because this is a difficult concept to understand, Fig. 24 shows a variation on the same principle.

In this example, 30 GPM enters the horizontal pipe at point A at 30 PSI. Ten gallons per minute then flow to sprinkler No. 1 and 20 GPM flow toward sprinklers No. 2 and No. 3. The pressure, however, at point A is pushing the water equally in both directions with 30 PSI. The volume splits but the pressure pushes equally in both directions.

The same situation occurs at point B where the water pressure is 30 PSI pushing toward sprinkler No. 2 and 30 PSI pushing toward sprinkler No. 3. In this case the 20 GPM splits, with 10 GPM going to sprinkler No. 2 and 10 GPM going on to sprinkler No. 3. The flow of water splits at each of these points but the pressure is pushing equally in each direction.