Shut down irrigation without leaving water in the line
TL;DR
Closing the valve on your irrigation system is only half the job. The water still sitting in the line is what splits pipe and cracks fittings once the cold turns up. Draining it takes an afternoon in September, and it saves you finding out the hard way in February.
Table of contents
- What actually breaks when you skip the drain
- Have a look at what you've actually got
- Three ways to get the water out
- The bits almost everyone forgets
- Where it's worth calling someone
- Do it in September, not on the first cold night
What actually breaks when you skip the drain
Nearly everybody closes the valve and calls it done. It looks finished, it feels finished, and in a mild winter it usually is.
Then you get one hard week in January and the whole lot lets go at once.
Water expands and the pipe doesn't
Water takes up more room once it freezes, roughly a tenth again on top of what it started as. Inside a sealed pipe, that extra volume has nowhere to go.
Something has to give, and it's always whatever was weakest. Usually a fitting, a valve body, or a run of poly pipe sitting close to the surface.
Why a closed valve feels safer than it is
Shutting the supply stops any new water arriving, which is genuinely worth doing. It just doesn't touch the water already sitting in fifty-odd metres of line on the other side of it.
That trapped water is the whole problem. A closed valve with a full line behind it is the exact setup that does the damage.
Where it usually splits
Damage turns up where water pools and where pipe runs shallow. Three places in particular:
- Low points in a zone, where water settles
- The valve manifold, which sits full at the best of times
- Anything crossing a raised bed or running along a wall
You won't spot a bit of it until spring, when you switch the system on and a patch of lawn starts bubbling at you.
Already found a split from last winter? Worth sorting that out before you spend an afternoon draining a system that needs a repair first.
📞 Call or text us on (604) 897-4989
Have a look at what you've actually got
Five minutes working out what's in your yard makes everything after this easier. Most systems around here follow one of a few patterns.
The backflow device
This is the assembly near where the irrigation line leaves the house, either in a box at grade or bolted to an exterior wall. Its job is stopping irrigation water flowing back into your drinking water.
It's also the priciest single part of the system and the one most likely to crack. It holds water by design, and it usually sits above ground where the cold gets at it. That combination is why it goes first.
The valve manifold and zone lines
The manifold is that cluster of electric valves, normally buried in a box with a green lid. One valve per zone.
The zone lines run out from there to the heads. Those long runs are holding most of the water in the whole system.
Poly pipe versus rigid PVC
Black poly pipe has a bit of give in it and will often ride out a freeze that would split rigid pipe. White PVC has no give at all.
Either one will fail with water in it, but PVC goes first. If you've got white pipe out there, treat the drain as something you simply do.
Pro tip: take a photo of the manifold box with the lid off before you start. Those boxes fill with soil and roots over a season, and a September photo makes spring troubleshooting a lot quicker.
Three ways to get the water out
There are three standard methods, and your system was built for one of them. Working out which one is the first real job.
- Manual drain valves, opened by hand and left to gravity
- Automatic drain valves, which release once pressure drops
- A blow-out with compressed air, one zone at a time
Manual drain valves
Some systems have little drain valves at the low point of each zone. Open them, open a head or two so air can get in behind the water, and let gravity do the work.
Give it longer than feels sensible. A long shallow run drains slowly, and wandering off after ten minutes is how water gets left behind.
Automatic drain valves
These open by themselves once pressure in the line drops far enough. Shut the supply, run each zone briefly off the controller to bleed the pressure, and they'll let go.
They're reliable right up until they aren't. A bit of grit holds one open or shut and you'd never know, so check a few heads for standing water afterwards.
Blowing the line out with air
The third way pushes the water out with compressed air, one zone at a time. It's the most thorough option and it's how most systems around here get done.
It's also the one with real risk attached. Too much pressure wrecks heads and fittings, and a small shop compressor usually can't shift enough air to clear a zone properly anyway.
The bits almost everyone forgets
Zone lines get all the attention because they're the obvious part. The forgotten bits are the ones that cost the most to put right.
- The backflow assembly, which holds water of its own
- Drip zones and the inline filter, both slow to clear
- The controller, which will keep trying all winter
The backflow assembly itself
Draining the zones doesn't empty the backflow device. It has its own test cocks and its own chambers, and they hold water quite happily.
Open the test cocks, leave the main valves sitting at about forty-five degrees, and wrap whatever stays exposed.
Drip zones and filters
Drip lines sit shallow and run at low pressure, so they hold water long after the sprinkler zones have cleared. The inline filter housing holds a cupful on its own.
Pull the filter out, tip it, and leave the housing loose over winter.
The controller
Nothing freezes in here, but a controller left running will cheerfully try to water a drained system in January. Switch it to off rather than pulling the plug, so your programme survives the winter.
Then write the shutdown date on a strip of tape and stick it inside the door. Future you will be grateful.
Pro tip: hose bibs are a separate job with their own steps, and even a frost-free tap needs the hose off it. Worth reading up on what's involved with outdoor taps while you're out there anyway.
Where it's worth calling someone
Plenty of this is yours to get on with. All five are fine jobs for a Saturday:
- Shutting off the supply
- Opening the manual drains
- Running each zone to bleed the pressure
- Pulling and emptying the filter
- Switching the controller off
Compressed air is where it stops being a weekend job. Air at the wrong pressure will fire heads out of the ground and split fittings you can't see. None of that shows up until spring.
The backflow device is the other one to leave be. It's the priciest part of the system and it needs annual testing by a certified tester anyway. A cracked assembly means a full replacement rather than a repair.
Same goes if the supply valve itself won't shut properly. A shut-off valve that's seized or weeping leaves you unable to isolate the system at all, and that's much better sorted before winter than after.
Pro tip: if a zone won't hold pressure while you're bleeding it, stop there and note which one it was. That's a sign of a leak you've already got, and pushing air through a line that's already split only makes it worse.
Do it in September, not on the first cold night
The reason this job gets left is that nothing bad happens for weeks after the last watering. The system sits there looking perfectly fine right through October.
Then the forecast turns, and by the time you've thought about it you're out there in the dark with a headlamp on, doing it badly.
An afternoon now costs you nothing but the afternoon. The same job rushed in December costs you fittings, heads, and quite possibly a backflow assembly.
Not sure which drain method your system was built for? Send us a photo of the manifold and the backflow device and we'll tell you what you're dealing with. There's a free quote in it if something needs replacing before winter.
