Large Scale Central

Water system question

Gardening
#1

My garden railroad has 3 mature redwoods in each corner with deep drip watering. Lately the drip has ceased working due to a couple of breaks in the 1/2" drip pipe. Some of the lines are almost grown into the base of the redwoods and the fibrous top roots is making it a challenge to dig. I’ve made the decision to cut the two main pipes that are underground at the point that is in front of the retaining wall and completely reroute the main pipes around the perimeter keeping everything above ground against the back fence and then feeding out to the trees. The PVC pipes from the valves to the garden look to be 1" and am wondering if I’d get better pressure reducing it to 3/4" or even 1/2" at the cut point?

I appreciate any thoughts/suggestions because watering systems is not my strong point.

Thanks,
Richard

#2

I honestly don’t know anything about watering systems. However I do believe that by reducing the pipe will only restrict the volume and not really affect/effect (for the spelling police) the pressure.

#3

I’m putting in a water system right now and thought I would get blinded by science, but then saw the light! :grin:

In a drip irrigation system, changing the diameter of the pipe feeding into the drippers can affect the flow out of the drippers, but the impact depends on the specifics of the system:

  1. Constant Pressure System: If the irrigation system is pressure-regulated (meaning it maintains a constant pressure regardless of changes in pipe diameter), changing the pipe diameter will have minimal effect on the flow out of the drippers. The drippers are designed to release a fixed amount of water at a given pressure, so as long as that pressure is maintained, the flow should remain consistent.

  2. Non-Regulated System: In a system without pressure regulation, changing the pipe diameter can impact the pressure within the system, which in turn can affect the flow rate out of the drippers. If the pipe diameter increases, the pressure drop along the pipe decreases, which can lead to a higher pressure at the drippers, potentially increasing the flow rate out of them. Conversely, decreasing the pipe diameter can increase the pressure drop and reduce the flow rate.

In summary, in a non-regulated system, the pipe diameter can affect the flow out of the drippers, while in a pressure-regulated system, the flow should remain consistent despite changes in pipe diameter.

Get blinded by science here…

This is related to Poiseuille’s Law, which describes the flow of a viscous fluid through a cylindrical pipe. Poiseuille’s Law specifically applies to laminar flow and is given by the equation:

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According to Poiseuille’s Law, the flow rate ( Q ) is proportional to the fourth power of the pipe’s radius (or diameter, since radius is half the diameter). This means that even a small change in the pipe’s radius (or diameter) can lead to a significant change in the flow rate if the pressure difference is held constant.

In the context of a drip irrigation system:

  • Non-regulated System: If you increase the pipe diameter, you effectively reduce the resistance to flow, which can increase the flow rate through the drippers if the system pressure remains unchanged. This is directly related to the ( r^4 ) term in Poiseuille’s Law.
  • Pressure-Regulated System: If the system is pressure-regulated, the flow rate through each dripper is controlled to stay constant despite changes in the pipe diameter. However, the pressure required to maintain that flow rate might change, but the actual flow rate through the drippers would not vary as much as in a non-regulated system.

So, Poiseuille’s Law is very relevant in understanding how changes in pipe diameter can affect the flow rate in non-regulated systems.

The take away answer is

  • the most significant change to flow will be the radius of the pipe to the power of 4. For example, change a pipe radius from 2mm to 3mm and your flow Q increases from 2x2x2x2 to 3x3x3x3 or from 8 to 81 times the flow.
  • So if you want more flow out of your drippers
  1. buy bigger diameter drippers (best option to increase flow by the power of 4)
  2. Increase your water pressure (but that only increases flow by the power of 1]

Your water saver feature on your shower and sink work the same way to save you money by narrowing your pipe and getting less water

#4

well, i am not as learned, as Bill is.
but as a (semi)desert farmer/rancher and a firefighter i learned by trial and error how to use water.
(i had about 5 acres of grapefruit and vegetables under drop-irrigation)

NO!!
the diameter of the pipe before the valves is the diameter you should use behind the vave as well.
(a bigger diameter behind the valve stores more quantity and costs more money but rends not more pressure. a smaller diameter auments friction = less pressure - as Bill’s table shows.)
(unless you split the line into two or more branches, where you have a high flow rate. but drip irrigation has a minimal flow rate)
if you don’t get enough water quantity to the trees, try:

  1. give each tree an additional drip-outlet.
  2. if the first tree in line gets more water, than the last in line, build a pipe"loop" that the water from the valve reaches the trees from both directions.

if the drip-outlets don’t give (enough) water, there are two possibilities:

  1. they are clogged. (dirty water, algae)
  2. your water source before the valve has not enough pressure.

if they are clogged, you could put a filter inline (but that costs pressure) and can evade to use other than black plastic pipes above earth (for less algae growth)

if the system does not get enough pressure - use drip-outlets made for more flow (less retaining)
or - now i’m talking money - put an automated pressure pump in-line, or use a watertower of more than six yards hight as feeder.

OR - just evolve a scedule, when to urinate against which tree. - that gives them not only water, but fertilizer too.

(thinking about pee-ing against a tree… trees need the irrigation not at the stem, but at the line defined by their crown-coverage. that is, where the fine roots are)

#5

In the camping/scouting outings they are called “Lavitrees”.