Blowing Out Sprinklers

Blowing out sprinklers before the deep freeze arrives is important.

Damage to a sprinkler system pipe occurs when that pipe remains partially or completely full of water during the cold winter months. In the winter, that trapped sprinkler water freezes.

Water expands as it freezes, and if the there's no place for the forming ice to go as it enlarges from the freezing process the greater volume of ice is powerful enough to rupture the sprinkler pipe.

I recently received this request for more information on blowing out sprinkler lines from Tom.

Preparing For Winter

"Hello, I'm preparing for winter conditions, with air temperatures in the subzero range, that may involve loss of electric power and natural gas for several days.

We have a Husky air compressor that we use for driving nail guns and small construction equipment like that.

The Details please...

Your suggestions are helpful. I have a few questions about details:

1) What kind of adapter should I use to connect the air hose to the water pipes?

Answer: Compressed air exits your compressor tank through a regulator (there should be a filter too, but many DIY compressors don't have one) and the air is stopped at the downstream side of the regulator with a "checked" coupler. "Checked" means that air can't flow until a connector is inserted into the coupler.

You then have to get the compressed air from the coupling on the compressor tank into your to your sprinkler lines to blow out the water.

A rubber or vinyl hose will do that for you.

One end of the hose will have a checked coupler, the other will have a connector. Insert the connector into the coupler on the compressor tank, and the air line will be charged. Air will flow down your hose to the next checked coupler.

One way to introduce air into the sprinkler system is to use a simple blow gun.

You attach the blow gun via it's connector into the checked coupler on the end of your hose.

If the water is off, the downstream line drain is open, and there is an opening into and at the highest part of your sprinkler system, then by pushing the nose of the blow gun into that opening and pulling the trigger, you will introduce compressed air into your sprinkler lines.

Did they install it correctly?

I would think that it would be a standard practice to plumb in a fitting where compressed air would be introduced to the sprinkler lines when it was time to clear them for winter.

If you know who your installer was, ask them. If not, examine the system to see if there is any access port into which you can insert a compressed air line connector, or which might accept one.

If you don't have one, you should. Get one installed. Or, acquire one of the standard adapters that have recently appeared on the market place for just this purpose.

If you had a compressed air connector at the highest point of your sprinkler lines (and since connectors are open, there would have to be a valve of some sort to stop the egress of water) when it came time to blow the lines, you'd simply shut off the water supply to the system, open the downstream drain, connect your air line to the connector on the sprinkler to allow compressed air to flow into the sprinkler system.

Next question is...

2) Is it necessary to blast the air into the pipes and force the water out quickly, or can I use less pressure for a longer period of time?

Answer: I don't believe it should make any difference!

Compressed air is a fluid, like water, and it will fill a vessel to full as it flows into it.

If there is a volume of water in your sprinklers that is filling a sprinkler line, compressed air will flow into the void upstream from that water, and then continue building up pressure until it drives the water out before it.

Compressed air wants to get back to atmospheric pressure, so it will continue to push towards an area of lower pressure (the open drain) until it gets there. Any water ahead of it will get pushed out.

The key is to have sufficient volume to adequately fill the sprinkler lines to ensure that all water is driven out.

Here is the intro page on compressed air & sprinklers which provides some basic guidance to figuring out how much compressed air you need.