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Thread: What is maximum PSI to blow water out of PVC pipes?

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    DIY Junior Member 920codyroad's Avatar
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    Unhappy Winterizing barn pipes, but not going as I had hoped. Help, please???

    We had some days where the temperature dropped to 18 degrees and the pipes in the barn froze and burst. I just got done replacing them. The pipes are 3/4 PVC. I installed a pneumatic coppling in the line inside the house where it is fed from. The run is about 75 feet from the house to the barn.

    I tested for water leaks and all is good. I hooked up the compressor to it and blew 70 PSI of air through. I would have thought the water would come rushing out when I turned on the spicket outside the barn. But, instead it just dribbled out. Once It stopped I would have thought I would hear the air rushing out of the spicket, but I don't. If I shut the spicket and let it sit closed for a few minutes and then open it slowly, the water and air start coming out. But, very slowly.

    What is the maximum PSI I can blow through 3/4" PVC? Am I doing anything wrong?
    Last edited by 920codyroad; 01-16-2010 at 03:36 PM. Reason: Changed title

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    DIY Senior Member gardner's Avatar
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    Quote Originally Posted by 920codyroad View Post
    blow through 3/4" PVC
    Personally I have had bad luck blowing pipes out. The problem with blowing the lines is that bubbles of air can travel freely through the liquid water, without moving much or any of it along the pipe. Water can easily flow back down the pipe to the low spot after you stop blowing air through.

    I prefer to design the lines so that that they pitch towards a low point, possibly in several places, and then place boiler drains at the low points. You should be able to drain the system dry by opening up all the valves.

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    DIY Junior Member 920codyroad's Avatar
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    Unfortunately, that isn't an option. The barn is on the same ground level as the house, the pipes to the barn are buried, both going to the barn and under the slab.

    The pipes coming out of the slab burst this week. I was lucky in that they burst and split about 6" above the slab. so, I had enough pipe to install a coupling and new pipes.

    But, I need to figure out a way to winterize these pipes. I would really like to have a blowout but don't know the maximum PSI I can push through without bursting pipes.

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    Test, Don't Guess! cacher_chick's Avatar
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    3/4" schedule 40 PVC pipe has a bursting pressure of over 1500 psi.
    That's not to say your joints or fixtures won't pop well before.

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    DIY Junior Member 920codyroad's Avatar
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    So, if I open the farthest spicket, I can pump 135 PSI (maximum my 60 gallon compressor goes) through without worrying about damage?

    What's the best way to get more CFM out of my compressor? I think it's volume that I'm after, not PSI.

  6. #6
    Test, Don't Guess! cacher_chick's Avatar
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    That will be fine as long as your system is in good shape.

    The actual compressor pump is where the CFM rating comes from. Bigger tank(s) and bigger line(s) will give your more CFM, but the pump will never keep up with a wide open hose.

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    Moderator & Master Plumber hj's Avatar
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    Default air

    All you need is about 5 psi to push the water out of the pipes, but you DO need enough volume to keep it moving. A compressor with a tank will usually have the volume needed.

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by 920codyroad View Post
    I need to figure out a way to winterize these pipes.
    75' of 3/4" ID is about 400 cu. in., about 1.7 gallons. Doesn't alcohol mix with water and prevent freezing? Or make all of it evaporate? Then you flush the pipe later?

    Is there some other liquid that is non-toxic with a low freezing point that doesn't react with the pipe material?

    http://wiki.answers.com/Q/What_is_th...g_point_of_rum
    Last edited by Thatguy; 01-17-2010 at 11:05 AM.

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    DIY Member gtmtnbiker's Avatar
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    What about using RV anti-freeze? That's what my in-laws use to winterize pipes in a summer house in VT.

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    General Engineering Contractor ballvalve's Avatar
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    Default suck it out

    Quote Originally Posted by gtmtnbiker View Post
    What about using RV anti-freeze? That's what my in-laws use to winterize pipes in a summer house in VT.
    A big shop vac or electricians vac will SUCK the water out and not just tickle the water with bubbles passing through.

    You could BLOW the water out using a "pig" - maybe a cotton ball or whole wheat bread ball, but only in a relatively straight line with out branches that lead to a shower valve or washer or toilet..... Read up on "pigs" online before attempting this creative approach.

    I would go for the vac unless you have a large diesel air compressor around the house. Volume is the key.

    When you replaced the pipes you should have used black 160psi poly. We go to about 10' here and they do not break.

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    Plumber Cass's Avatar
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    Something is wrong...with 70 PSI, and I am assuming you used a compressor, you should have had the water flying out and when the water was pushed out there should have been tons of air...is there a check valve somewhere on the line????

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    Test, Don't Guess! cacher_chick's Avatar
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    I was more under the impression that there is probably still ice in the line.

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    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by cacher_chick View Post
    I was more under the impression that there is probably still ice in the line.
    A strong possibility.

    I use my compressor to blow out the sprinkler lines each Fall. The procedure calls for a 50 psig regulator setting. I have a reasonably large portable tank and moderate size compressor but it still depletes the tank several times. As the heads clear of liquid the volumetric rate of air uptake shoots up and the pressure begins falling.

    Quote Originally Posted by That Guy
    Is there some other liquid that is non-toxic with a low freezing point that doesn't react with the pipe material?
    Don't know about it's affect on the plastic pipe, but propylene glycol is the base for non-toxic anti-freeze used in cars these days.

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    General Engineering Contractor ballvalve's Avatar
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    Quote Originally Posted by Thatguy View Post
    75' of 3/4" ID is about 400 cu. in., about 1.7 gallons. Doesn't alcohol mix with water and prevent freezing? Or make all of it evaporate? Then you flush the pipe later?

    Is there some other liquid that is non-toxic with a low freezing point that doesn't react with the pipe material?

    http://wiki.answers.com/Q/What_is_th...g_point_of_rum
    Vodka is fairly non toxic and you can use it to celebrate the spring thaw if you save it when you refill the lines.

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