Blowing out water pipes

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Blowing out water pipes

by Phillip

I am planning to buy a compressor to blow out water pipes for winter. The pipe is 3/4 inch and approximately 50 feet long.

What size compressor would I need?

Phillip

Bill answers...

Hello Phillip:

Yes, it's getting to be the time of the year in the Northern Hemisphere where we have to be concerned about water freezing in pipes that are exposed to the frigid wintertime conditions.

What you need to blow out a fairly small water pipe as you've outlined above is a small compressor.

Let me ask you, are you just going to use the compressor for this? If so, then perhaps you might rent an air pig or small air tank, fill it up with compressed air at the local gas station, and use that to blow the lines instead of buying an air compressor.

On the other hand, once you've got an air compressor, you'll find lots of uses for it.

In order for the water line to be voided of water, you need to fill it with compressed air fairly quickly. The compressed air, flowing into the water pipe, will drive the water before it and out the other end.

If the water pipe is metal, you can use compressed air at industrial pressures...perhaps 120 PSI or so. If it's not, make sure that the pressure you use doesn't exceed the burst pressure of the pipe, or you might be creating more problem than you wish.

Here's more information about that.

If my math is correct (and yes, you do want to check it) a 3/4" pipe x 50' will hold about .2 cubic feet of air. If you introduce a few cubic feet of compressed air at, say, 30 PSI, you'll have plenty to drive the air out of the pipe, as long as the outlet is below the air inlet.

If there's convoluted piping, add higher pressure (maybe 50 PSI if the pipe can stand it) and get the flow of compressed air going into the pipe as fast as you can to build the volume of air inside the pipe quickly, to drive the water out before it.

It will help if the outlet from the pipe is as large a possible to allow the water to get out more easily. Open the drain tap fully.

When all that's coming out of the outlet at the end of the process is a little mist or just air, you're done.

So, a small compressor that has a tank that holds 2-3 cubic feet of air, one with a regulator to reduce the outflow pressure if need, and an air hose with a high flow blow gun is what you'll need.

Hope this helps,

Bill

Comments for
Blowing out water pipes

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Jan 02, 2010

Reduced water pressure
by: Anonymous

I added a water line for my new frig to make ice cubes, but when was finished, the water presssure in the kitchen was reduced in half! Do I have "junk" building up in my water pipes? I have a compressor, but if I blow out the pipes, will it clean out the junk in my pipes? AND, how/where would I hook up the compressor to blow out the pipes? Please help an old grandpa figure this one out...
________

Howdy: I, too, have added a water line to a fridge from the water supply, and no way should that have reduced water pressure in the kitchen.

I expect you shut the water off in the area you were adding the new line, and my thought is that the valve you used to shut off the water isn't open all the way, and may be throttling water and lowering water pressure.

Could you have junk in your water lines? Maybe. No way I can tell. If you do, it will be a build up of scale likely, and I don't think trying to clear that with compressed air will bring any success.

When blowing out water lines, you need to add a fitting somewhere to which you can attach an air supply. You normally won't find one of these in a kitchen water supply, sorry.

Cheers & Good Luck.

Bill

Nov 24, 2009

using shopvac to blow out water from pipes
by: telecomtom

Hello Bill, how about the comment from Anonymous about using a shopvac to force out the water? the pipes were 1 1/4" diameter, which is larger than the water lines in my house (about 3/4" I think). There would have to be a battery or gasoline-powered generator to run the shopvac or compressor for however long it would take to get all the water out.

Another problem I might have is "dead ends." How to get the water out of the end of a pipe that is closed. For example, we were going to install a standard water heater (with tank) but opted for a tankless model instead. The pipe that was going to connect to the water heater is stubbed out, with an end that doesn't open. How does that work when the compressed air reaches that point? It seems like the water would just get stuck in the end and then would freeze when the house temperature drops below 32 F / 0 C.

These are interesting puzzles. But very real for some people like my humble self....
_____________

In order for the shop vac to work, you have to have air ingressing at the other end of the system. The vacuum pulls the water out...yes, but it can't pull the water if nothing is flowing in to replace it.

A power supply for a shop vac, as you point out, can be a problem. The same can be said for a compressor too, of course.

If the lines that are plugged are oriented downwards, and water cannot flow out as the rest of the lines are voided, then yes, you may have a problem.

Even using compressed air may not solve that one.

It seems to me that anyone installing a sprinkler should make sure that there is an access point at the end of all runs to allow the connection of an air line to blow the lines... but then, that costs more money, doesn't it.

Good luck.

B.

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Nov 24, 2009
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Submitted by: telecomtom

Title

Comment
Hello Bill, how about the comment from Anonymous about using a shopvac to force out the water? the pipes were 1 1/4" diameter, which is larger than the water lines in my house (about 3/4" I think). There would have to be a battery or gasoline-powered generator to run the shopvac or compressor for however long it would take to get all the water out. Another problem I might have is "dead ends." How to get the water out of the end of a pipe that is closed. For example, we were going to install a standard water heater (with tank) but opted for a tankless model instead. The pipe that was going to connect to the water heater is stubbed out, with an end that doesn't open. How does that work when the compressed air reaches that point? It seems like the water would just get stuck in the end and then would freeze when the house temperature drops below 32 F / 0 C. These are interesting puzzles. But very real for some people like my humble self.... _____________ In order for the shop vac to work, you have to have air ingressing at the other end of the system. The vacuum pulls the water out...yes, but it can't pull the water if nothing is flowing in to replace it. A power supply for a shop vac, as you point out, can be a problem. The same can be said for a compressor too, of course. If the lines that are plugged are oriented downwards, and water cannot flow out as the rest of the lines are voided, then yes, you may have a problem. Even using compressed air may not solve that one. It seems to me that anyone installing a sprinkler should make sure that there is an access point at the end of all runs to allow the connection of an air line to blow the lines... but then, that costs more money, doesn't it. Good luck. B.

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Nov 23, 2009

Air Tank/ Air Compressor - blowing out lines
by: Tim

I am getting ready to try this for winterizing a small farmhouse in the mtns of North Carolina. I am not sure if an air tank or air compressor would
be better. Since this is the first time, I want to get it right. Any thoughts/ ideas????

Thanks, Tim
__________
Hi Tim:

It's not hard to do, but you do need to know how much air you will require. A single, charged portable air tank, while providing lots of pressure, may not have enough volume to rid your lines.

Please see the details on this, and linked from, these pages about blowing out sprinkler lines.

Bill

Feb 02, 2009

Use a shop vac instead?
by: Anonymous

I blow out swimming pool lines (1 1/4 diameter 25 - 40 feet) with a small sized shop vac. You can run it continuously until the lines are bone dry.

Dec 28, 2008

details
by: telecomtom

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 nailguns and small construction equipment like that.

Tom...too many subjects to answer here. Please see:

www.about-air-compressors.com/blowing-out-sprinklers.html

Cheers,

Bill

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Blowing out water pipes

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Blowing out water pipes