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Old 03-19-2013, 12:06 PM   #1
Jim M
 
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Unhappy Air compressor

Would like advice as to how robust an air compressor is needed for winterizing blow-out. Is a relatively cheap Craftsman 1.5 gal., 0.6 HP, 2 CFM at 90 psi good enough.

I did my first Airsteam winterizing by just draining everything and then adding anti-freeze. That was all I need to do with the pop-up I had before the AS. Didn't work. Had a cracked valve in the shower and the black tank flushing line when I got to Palm Springs in January.

It did get down to 20 below this winter in Durango.
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Old 03-19-2013, 12:18 PM   #2
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That's pretty small in capacity and especially CFM. It could work, but you would have to keep shutting off and on the individual valves to allow the compressor to build up pressure and enough volume to blow your lines out. It would just take longer.
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Old 03-19-2013, 12:23 PM   #3
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A little more CFM would be nice, or as hhendrix said, it will take a little time.

I have a smaller compressor. It will run a HVLP paint gun ok, but an impact wrench taxes it some.

I have had good success with it for several years.

I add no antifreeze, except to the traps.

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Old 03-19-2013, 01:58 PM   #4
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Quote:
Originally Posted by Jcmohle View Post
Would like advice as to how robust an air compressor is needed for winterizing blow-out. Is a relatively cheap Craftsman 1.5 gal., 0.6 HP, 2 CFM at 90 psi good enough.

I did my first Airsteam winterizing by just draining everything and then adding anti-freeze. That was all I need to do with the pop-up I had before the AS. Didn't work. Had a cracked valve in the shower and the black tank flushing line when I got to Palm Springs in January.

It did get down to 20 below this winter in Durango.
Blowing lines and keeping a small electric heater going is all I do down here in the winter, but we rarely go below 25 degrees. At 20 below, there probably is not a compressor big enough to blow the lines adequately to prevent freezing.

If I had to winter in those temps, I would install one of those fittings that allow you to inject antifreeze directly into the water pump, bypass the water heater, and then after draining all tanks, and blowing all lines, I would inject antifreeze and run it thru all the water lines and fittings.

Or, I might just go South for the winter.
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Old 03-19-2013, 03:23 PM   #5
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Once you blow the water out it doesn't matter how low it goes. But you gotta be sure you got it all and you need a compressor with decent air volume to do that. I turn mine down to 40 / 45 lbs. and just let it go while I open each valve. I go around 2 or 3 times to make sure I got it all. Don't forget the low point valves and toilet and sink sprayer if you have them too. I disconnect the shower hose also. Antifreeze into the traps and bowl and I've been good here down to near 0 deg.
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Old 03-19-2013, 03:37 PM   #6
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Originally Posted by Jcmohle View Post
Would like advice as to how robust an air compressor is needed for winterizing blow-out. Is a relatively cheap Craftsman 1.5 gal., 0.6 HP, 2 CFM at 90 psi good enough.

I did my first Airsteam winterizing by just draining everything and then adding anti-freeze. That was all I need to do with the pop-up I had before the AS. Didn't work. Had a cracked valve in the shower and the black tank flushing line when I got to Palm Springs in January.

It did get down to 20 below this winter in Durango.
Airstream service schools, suggested a 5 HP compressor be used for winterizing.

Andy
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Old 03-20-2013, 07:05 AM   #7
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I've found you don't need a super-large compressor, but what can happen is that it'll run for a while, which can be hard on a lighter-duty compressor. Mine now has that slightly "burned" smell when it's running...sigh...and it wasn't a super cheap one, either. I'll admit mine was probably really designed to operate a nailer or something like that, so it was built with the sense that it would fill up the tank, cool off, then refill the tank some time later. Unfortunately, with winterizing, it takes a while to pressurize the entire system - tank, hose, and water system - and you lose quite a bit of pressure every time you open a valve, so it's easy to run the compressor too long. (Remember, pressure alone does no good - it's relieving that pressure, which causes the water to move toward valves, that does the job.)

For winterizing, you almost want a compressor with decent ability to run non-stop for an extended time, without air tanks - they're actually not helping matters at all for this purpose, and in fact can hurt because the first thing the compressor has to do is fill the tank. Unfortunately compressors with heavy duty cycle are fairly expensive, and they usually include a tank, which as I just said is counterproductive...

You can do it with a cheap compressor...you just have to be careful. Andy's recommendation of a 5 HP compressor sounds like a good idea to me, but those are starting to get into the fairly expensive range. I almost want to install something like this, but without the tank. (It's not unusual for me to winterize two or three times in one winter season, so although we've only had our trailer less than two years now, I've already built up some good experience winterizing it.)
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Old 03-20-2013, 07:12 AM   #8
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Whatever you use, let the pressure build up and then open a valve. The pressure will build up faster with a bigger compressor.

Perry
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Old 03-20-2013, 07:31 AM   #9
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I've found you don't need a super-large compressor, but what can happen is that it'll run for a while, which can be hard on a lighter-duty compressor. Mine now has that slightly "burned" smell when it's running...sigh...and it wasn't a super cheap one, either. I'll admit mine was probably really designed to operate a nailer or something like that, so it was built with the sense that it would fill up the tank, cool off, then refill the tank some time later. Unfortunately, with winterizing, it takes a while to pressurize the entire system - tank, hose, and water system - and you lose quite a bit of pressure every time you open a valve, so it's easy to run the compressor too long. (Remember, pressure alone does no good - it's relieving that pressure, which causes the water to move toward valves, that does the job.)

For winterizing, you almost want a compressor with decent ability to run non-stop for an extended time, without air tanks - they're actually not helping matters at all for this purpose, and in fact can hurt because the first thing the compressor has to do is fill the tank. Unfortunately compressors with heavy duty cycle are fairly expensive, and they usually include a tank, which as I just said is counterproductive...

You can do it with a cheap compressor...you just have to be careful. Andy's recommendation of a 5 HP compressor sounds like a good idea to me, but those are starting to get into the fairly expensive range. I almost want to install something like this, but without the tank. (It's not unusual for me to winterize two or three times in one winter season, so although we've only had our trailer less than two years now, I've already built up some good experience winterizing it.)
Sorry, but I disagree with this idea. It's really not the pressure, but the air flow thru the lines that blows the water out, and for that you don't need much pressure (as a matter of fact, the air pressure should be regulated to 50 PSI or less). What works best is a compressor with a large tank, or reserve of pressure, that will maintain the air flow thru the line long enough to first blow most of the water out, and then continue the air flow long enough to dry the line.

I have a 2HP compressor with a 20 gallon tank, and it does a great job.

As an example, you could put 100 PSI on the system (assuming nothing would rupture), and if you didn't open a valve and let the air and water flow thru the pipes, you would accomplish nothing.

On the other hand, if you put only 10 PSI on the system, but had 100 CFM of flow, you would blow the water out and dry the system very easily.

Additionally, there is some needed procedure also. I first drain all the tanks, water heater also. Then I open all faucets, open the low system drains to get as much water out as possible. Then I blow the lines, one faucet at a time, with the air pressure. However, even then, there will be some water left in places like the inlet line and filter to the water pump, and the pump itself. That's why I keep a heater going when freezing weather down into the 20's is predicted.

Granted, we don't have the cold that you folks up North have, but in the worst we've had here (a couple of days in the teens), I've not had any freeze damage using this procedure.
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Old 03-20-2013, 08:09 AM   #10
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The flow is limited by several factors. The pressure differential across of slug of water is what is going to push it out of a low spot. The lines in the trailer will act as an accumulator and allow much larger short term flow rates than what you will get after a few seconds when it is all what the air compressor can cram through that little hole at the end of the quick disconnect on your air line. The size of your air compressor tank is a big factor as well and will maintain flow rates much larger than what the compressor can produce. Yes a big compressor with a big tank will get it done faster. If you want flow rate run a 3/4" line directly from your air compressor to your hose connection. Better yet, use a garden hose instead of an air hose. Now your flow rate restriction is your air regulator or the water pressure regulator/flow restrictor in your camper. There are a lot of restrictions that make the size of the compressor less a factor. I have two degrees in Aerodynamics and Fluid mechanics. It there is a small amount of water in the lines, it won’t hurt anything. Leave valves open so any residual water can expand without busting something. The toilet valve seems to be the worse place for water to hide in my trailer because it is at the low point in the line and it keeps a slug of water above it to fill the bowl. Make sure you blow water out the low point drains. Drain the water heater and replace the plug and open valves one at a time and then go back and blow them out again because the water can go from one place to another.

Perry
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Old 03-20-2013, 09:45 AM   #11
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A friend of mine doesn't have a check valve in the city water line and uses a shopvac to suck the water out the bottom instead of fighting gravity. You might also be able to use a shopvac to blow out the lines with it's low pressure/high volume design.
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Old 03-20-2013, 09:49 AM   #12
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Sorry, but I disagree with this idea. It's really not the pressure, but the air flow thru the lines that blows the water out, and for that you don't need much pressure (as a matter of fact, the air pressure should be regulated to 50 PSI or less). What works best is a compressor with a large tank, or reserve of pressure, that will maintain the air flow thru the line long enough to first blow most of the water out, and then continue the air flow long enough to dry the line.

I have a 2HP compressor with a 20 gallon tank, and it does a great job.

As an example, you could put 100 PSI on the system (assuming nothing would rupture), and if you didn't open a valve and let the air and water flow thru the pipes, you would accomplish nothing.

On the other hand, if you put only 10 PSI on the system, but had 100 CFM of flow, you would blow the water out and dry the system very easily.
This is what I was trying to say. Thanks for clarifying it!
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Old 03-20-2013, 09:51 AM   #13
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I dissent from the big compressor advocates.
I have been blowing out the lines of my 25 Safari with a $40.00 125 volt tire inflator for years. The AS makes it undamaged through the Colorado mountain winter where it gets to minus 25 or below.
I drain everything including the water tank grey and black tank and hot water heater, put the plug back in the water heater, hook up the inflator with an adapter and get to work. I turn on faucets one at a time until there is nothing but air. I go back over the same faucets a couple of times until I hear no bubbling, nothing but air hissing out the faucet. This takes less than the 10 minutes the instructions on the inflator say is maximum run time. The inflator is cool to the touch, running it at a high pressure is what causes it to heat up.
I disconect the lines to the water pump and let it run for a couple of seconds to pump out the water.
Last, I put rv antifreeze in the traps putting enough in (a gallon total) so that there is anti freeze in the tanks to prevent the knife valves from freezing. That's it, done, total time about 45 minutes.
I have plastic water lines in my AS (but metal faucets). There is room for a little expansion in those lines. I am sure I have drops of water in my lines but not enough water to cause freeze damage. I have inspected my water lines and have no dips in the lines that would allow solid water to collect.
Some of the older 'AS's have copper lines. I make no representation about whether the inflator would work on copper piping where there is no room for expansion.
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Old 03-20-2013, 10:03 AM   #14
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Does it matter if you use an oil less compressor or one that has a crankcase? The one I have needs to have the oil checked and added to now and then, must go somewhere. Seem to recall it wasn't a recommended compressor for painting for that reason. Have to wonder if it also puts a small amount of of compressor oil into the water lines??? Is there a filter that will trap the oil?
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