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I am looking to winterize my irrigation system: I called a professional company last year, and they charged me 100$ for essentially 15 min of work. One of the guys said that this was super easy to do if I wanted to do it myself next year, which indeed sounds interesting.

I have a compressor and an adapter that allows me to blow air through the system (I just bought one).

I watched videos on the topic and I believe I understand the process pretty well:

  • Enable/open one circuit at a time through the control panel.
  • Blow the air with the compressor until no water comes out of the circuit. Not for too long to avoid damaging/melting the sprinklers.
  • "Rince and repeat" for the other circuits.
  • Make sure the water input stays closed throughout winter :)

Now, most of the videos on the Internet show an underground box with knobs and pipes that one can shut off/on.

In my case, while I do have that box - picture 1 below - it only contains the electro-valves and there is no additional knob or input in there, to shut anything off or for me to plug anything into.

Box in the ground - no input or know there

The only pipe that comes to that box is directly connected to a hose bib in the wall - see picture 2 - in a permanent way: it cannot be unscrewed. The hose bib has a secondary output with a knob though: we usually use it to water manually some plants not covered by the sprinkler system. The host bib has a main knob on the top that cuts water supply to both ends.

Hose bib right on top of the ground box

Now my question is probably stupid, but you never know:

Am I right to assume that I can just:

  • Shut off the main knob (on top), effectively preventing any water from going in the system.
  • Open the secondary knob and plug my air compressor on it to start the water-draining process through there.

I am mainly worried about somehow destroying the hose bib with too much pressure or something. It may be silly.

Additionally : I haven't used a compressor before, is there any pressure setting/value that I should be aware off not to burst the pipes? Anything else I should be aware of?

Thank you.

P.S: My compressor is this model in case it matters. I've read in many places that it was more than enough for the task, provided I am a bit patient in between-circuits.

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    Most air compressors have a valve/handle to adjust output pressure, so 30/40 pounds should be enough, instead of full pressure output.
    – crip659
    Oct 11, 2022 at 21:23

2 Answers 2

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Your compressor can deliver far more pressure than your irrigation pipes can withstand. Maybe it's adjustable, otherwise without a suitable regulator it could damage your pipes and sprinklers. It can deliver 165psi, you want 50 at most, probably less.

Your compressor cannot deliver enough air volume to winterize an irrigation system. It's 2.6CFM. You want at least 20, probably more.

Your procedure is more or less correct except that you need to manually turn on one valve at a time (in the green box) to blow out one zone at at time. You say there are no manual adjustments in there. You are probably wrong. Pictures would help. But if it's true, you will need to do it using your system controller.

Some advice: I love DIY and I love saving money but blowing out the sprinklers is one of the things I farm out. You cannot justify purchasing and storing a compressor big enough for the task if you won't use it for anything else. Even renting one for a day will cost more than a landscaper will charge.

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  • When it is blown out, to save problems in the spring disconnect the second valve from the hose bib and cover the hose with plastic wrap or whatever to keep water and other things out. The reason if your hose bib leaks it will freeze in the valves and you will get a first hand experience on changing them. I would suggest since you do not have a usage for the compressor shop and hire the job or get some neighbors and rent one.
    – Gil
    Oct 11, 2022 at 21:47
  • Thanks for your answer, and just for my understanding: the (S)CFM is about the quantity of air that the compressor can deliver without losing pressure, is that correct? So I assume the rationale for the bigger compressor is to be able to maintain said pressure until the whole waterline is filled with pressurized air?
    – ereOn
    Oct 11, 2022 at 21:49
  • The trick is that the sprinkler heads will start blowing air once they have blown out water. If you can't maintain pressure on the section of pipe sufficient to blow air from all the sprinkler heads, the ones further along won't blow out water after a few have blown out water and started blowing air. If you have a very large tank you can do that with a small compressor (and then wait a long time), but you are exceedingly unlikely to have a very large tank with a small compressor.
    – Ecnerwal
    Oct 12, 2022 at 0:22
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I am fortunate enough to have a large compressor in my shop. Blowing out the sprinkler system consists of the following steps:

  1. Turn off the water to the system,
  2. Run an air hose from the compressor to a regulator then to an inlet on the double check valve that's intended for blowing out the system.
  3. Set the pressure on the regulator to about 35 psi and connect the air hose after having relived residual pressure by manually opening one zone for a minute or two.
  4. Run the "test program" on the system controller, on my controller the test program runs each zone for a short time, I think the default is 2 minutes. That's enough time to blow most if not all of the water out of the system. The sprinkler heads will start spinning really fast or whistling when the last of the water is expelled.

Now, all that said, you may not have a system controller that has a test pattern, but nearly all of them have a manual "water now" capability which could be used in it's stead. It does take a large compressor to make it all work.

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  • Thanks for your answer. I've seen highly divergent opinions on whether a small compressor would do the job - although, much more slowly. I haven't read a good scientific explanation as to why it would or would not work though. I am not trying to be cheap but rather to understand what makes a difference. I guess I'll stay on the safe side and pay the service though.
    – ereOn
    Oct 11, 2022 at 21:57
  • What happens is a small compressor can't deliver the volume needed and pressure drops to maybe 5-10 psi...been there, done that! Of course a lot depends upon your configuration. If just a few heads on a zone, it might work, but if you have a large system with like 10-20 heads, as they said in the movie Jaws, "We're gonna need a bigger boat". :) Oct 11, 2022 at 22:17
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    @GeorgeAnderson Just saw on facebook yesterday that the quote is really "you are going to need a bigger boat"
    – crip659
    Oct 11, 2022 at 22:22
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    @crip659 LOL, but I think I'm close enough! The OP is either going to have to farm this out, or rent a larger compressor. Oct 11, 2022 at 23:57

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