It is that time of the year for north America: the temperature will soon drop below the freezing point. The strangest thing about water is that it expands as it freezes. Most liquids would simply shrink as it becomes harder for the thermal energy to overcome the inter-molecular attractive forces. As molecules get closer, they form a well defined crystal structure which is typically more compact compared to the liquid form.
Water will behave similarly until 4 degrees Celsius. But at that point, the interaction among the hydrogen elements start dominating. The ice is hydrogen bonded in an hexagonal crystal structure. This results in a less compact packing, hence the expansion. This is why pipes will burst in winter if water freezes in them. It is also why there is life on earth because lakes start freezing on the surface as the colder water floats due to its lower density. The ice forming at the top creates an insulating layer so that the whole lake will not freeze and fish will live to see another summer.
I lived in parts of the US where the temperature reaches the value at which Celsius and Fahrenheit measurements will read the same number. If you leave water in sprinkler pipes, there is a good chance they will burst. You need to get the water out. Newer systems are built such that there will be enough slope, and the water will self drain if you simply cut off the water and open a couple valves. For the rest, you have to pump in high pressure air to push the water out. I have been winterizing my sprinkler system myself for the last 10 years, and never had issues. So I decided to put this out there in case someone finds it useful. There are nice Youtube videos too. It is not rocket science, but one needs to be careful to not end up with burst pipes.
My major difficulty was that I didn’t want to buy and store a compressor with an humongous tank. I have been using a 3 gallon pancake compressor. People will say that it won’t be enough to remove all of the water out, but I don’t quite agree with that. You just need to take it slowly and be patient. And another trick is to do this at least a couple weeks before temperatures drop below freezing. That will be enough time for the remaining water to evaporate.
Another issue I had was that all the input connections were before the back-flow valve. There is a small spring that presses a gasket down. In the normal operation, the water pressure will easily push it up and seal the system. If the city water pressure is down for some reason, the spring will make the gasket drop down, opening up the line. this will prevent any back flow from the sprinklers back to the city water system, hence the name back-flow (prevention) valve.
This means that the incoming air from the compressor has to seal the valve by pushing it up. But you can’t really do that with a small compressor since flow is rather limited. That’s is where I had to do some hacking. I first removed the gasket assembly and drilled a small hole as Fig. 1.
Figure 1: I drilled a hole on the plastic so that I can catch and pull the gasket assembly up.
I installed it back in place, and reached in to the hole with the tip of a nail to push the gasket up to seal the system as in Fig. 2.
Figure 2: The hacked set up with a nail keeping the gasket pressed to the top to help seal the system.
I tied a small rock on the other end of the nail to keep the gasket gently pressed. It doesn’t need to seal it perfectly by itself. It just needs to keep the gasket gently pressed. As I tie in the compressor, the air pressure will self-seal. With this trick, I was able to keep the air in the system until I manually twist the zone valves, see Fig. 3, one by one. I do 3-4 rounds for each zone. After the third round, it will be mostly a mist of water coming out.
Figure 3: I have a total of 4-zones to clear. I did upto 4 rounds for each zone.
Once I am done, I drain the water between the back-flow valve and the main valve using the draining knob as in Fig. 4.
Figure 4: The main valve and the draining screw.
In the text above, I didn’t mention a couple of critical steps. Here is the chronological order of steps:
- Plan to do this a couple weeks before temperature drops below zero.
- Make sure you know the locations of each zone and sprinkler heads. If you don’t, just do another round of watering and make a map.
- Shut down the water to the sprinklers (the valve is typically in the basement.)
- Make sure you wear safety glasses. Things may fly around if the connections give in.
- Set the output pressure of the compressor to 50psi max.
- Connect the air compressor to see if it will provide enough flow and pressure to make a seal. If so, you don’t need to drill holes or hack anything.
- Turn each zone on manually and let the air flow and push the water out, and turn it off to wait for your compressor to gather a few more gallons of air. Repeat a few times and go to the next zone. I sometimes to another round with for each just to make sure.
- When all is done, disconnect the compressor. Wrap the whole assembly with some plastic bag to prevent any water to get in and freeze.
- Drain the water between back-flow valve and the main valve.
And that’s it!