21-day lockdown – Day 5 – Fixing pressure problems with your irrigation system


21-day lockdown – Day 5 – Fixing pressure problems with your irrigation system

Now that you’ve planted your veggies, and are thinking about ways to encourage insects to visit your garden, we thought we’d shift tack for today and discuss how you can fix some of those nagging and annoying irrigation problems you might have in your garden. Over the past year we’ve helped a number of clients who have had pressure problems with their irrigation systems, specifically in suburbs such as Fourways, Jukskei, and Lonehill, where the municipality reduced the size of one of the main water pipes, thus affecting the pressure to homes in these areas. These pressure changes may not be noticeable in general household use, but they are very noticeable in an irrigation system which has been setup to use all of the available pressure and flow. So let’s discuss a real-world example, and perhaps you can use some of these ideas for your own system.

Note: Adjusting your system requires a basic understanding of how sprinklers use water – which is a little bit of maths – but we’ll discuss this as simply as possible. As always you’re welcome to send through your questions.

“Sorry, you can’t have an irrigation system.”

A few months back I was called to a small garden in a retirement village. I happened to be working in one of the neighbouring properties, and the client decided it couldn’t hurt to ask me to come and have a look at his system. He’d had the system installed by a friend, but due to changes in the estate’s water pressure, the system no longer worked, and was only dribbling water onto his lawn and his beds. By the time I got there he’d already been told – by a fairly reputable irrigation company – that he “couldn’t have an irrigation system”, because his water pressure was too low.

I do not know what was discussed with this other company, so can’t comment on why they weren’t able to provide a solution, but to my mind there were five different ways to solve this client’s irrigation pressure problem, all with pros and cons. In the end we managed to choose one that didn’t break his budget, and was minimally invasive with regards to trenching. It’s a solution you might be able to implement yourself (but probably only once the lockdown is over, so you can get the necessary materials)

Firstly, here was the original layout:

Some details on this:

  • The garden was split into two sections, lawn and beds
  • The pressure and flow from the tap where the system was installed was 5 litres/minute at 2bar, and 9 litres/minute at 1.5bar (note: these are very low figures – it’s probably no wonder he’d been told he couldn’t have an irrigation system!)
  • The original design used two cone nozzles for the lawn – a 17foot and a 15foot, both on 90 degree arcs – and 13 microjets for the beds.
  • The controller was a single-station controller – meaning if he wanted to use it, he’d have to irrigate his whole garden at once

Controllers such as this Orbit model can only run one station

At this point, it’s worth briefly mentioning how pressure and flow works: essentially, the more water (flow) you try and use, the less pressure you’re going to have on your system. Think of this in terms of your shower: if someone opens all the taps in your house whilst you’re showering, you might have very little pressure to shower properly. The sprinklers in your garden are the same. They all use a certain amount of water, but they also need pressure to distribute it effectively. Use too many sprinklers, and the pressure in your system drops. How much pressure do sprinklers need? This varies between model and manufacturer, but for cone nozzles the ideal pressure is usually between 1.5 – 2.5 bar.

Which brings us to the original irrigation design. In order to have pressure for his sprinklers, our client needed to use no more than about 9 litres per minute, which would give a pressure rating of about 1.5bar. But as you can see, his sprinklers were trying to use 21 litres/minute, which meant there was no pressure on the system at all.

Here were the options to solve the problem:

  1. Increase the pressure at the mains
    This may be an option on some systems. In some scenarios the pressure valve at the mains to the house can be set too low, and can be adjusted to increase pressure for the tap that feeds the irrigation system. One needs to be careful doing this, because there are usually valid reasons why a particular valve has been set the way it has – you don’t want to end up with burst geysers or pipes. But in general, it’s worth checking if this can be done.
    Note: It’s also worth checking if there are any blockages at the mains, such as a clogged filter or faulty isolation valve
  2. Connect a new main line from the mains
    This was the most expensive option. It required adding a new main line that was independent of the household supply, thereby eliminating the pressure reducer and reducing friction-loss, since you can choose a larger pipe than that laid by the developer. Most new irrigation installations should use their own main lines, but cost-wise this wasn’t an option.
  3. Redesign the installation using a 2-station controller
    Again, this was another costly option. It meant re-trenching much of the garden to cater for a second station, and purchasing a new 2-station controller. Had we originally installed the irrigation we would have designed it this way.
  4. Install a tank and a pump, and control the pressure yourself
    This is the best solution for clients who don’t want to rely on their estate or municipal supply. By installing a tank and a pump you can control the pressure and flow indefinitely, and bypass any municipal pressure issues you might have.
  5. Change the sprinkler types, and adjust their positions
    This was the option we selected for this client, and although it wasn’t as perfect as I would have liked it, it allowed him to once again have a functioning system.

 

Here was the new design:

These were the changes: 

  • we changed point 1 on the lawn to a 15ft nozzle, which saved about 1 litre/minute.
  • we moved point 2 on the lawn to the top of the slope, which reduced the arc from 90 degrees to 33, thereby saving another 2.2 litres.
  • we changed the micros in the beds to MP Rotators, and relied on lawn point 1 to water the bed at the end of it’s radius. Additionally, we reduced the MP Rotators by 25%, thereby further reducing the water used on the system. This saved nearly 10 litres/minute.

Note: It is advisable not to use rotary nozzles – such as the Hunter MP Rotators – on the same station as cone nozzles, because the two have different operating pressures, and because rotary nozzles have lower precipitation rates. I decided to make a concession in this scenario because the beds required less water than the lawn anyway, and because the operating pressure on the system, whilst still very low, was still sufficient to run the MP Rotators.

Although this isn’t an ideal scenario (there is no head-to-head, and the pressure on the system is still very low), it did allow our client to once again have a functioning system.

Note: In case you’re wondering, there is also another sprinkler type we could also have employed here: a drip-line for the beds!