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Thread: Capillary Action

  1. #1 Capillary Action 
    Time Lord zinjanthropos's Avatar
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    A friend called me over to look at the propane stove in his RV. The maximum flame was very low and had a bouncing affect. From my gas fitter days I said it appeared as if water was in the line. Outside he had two hoses for two propane tanks. One was connected to a tank while the other dangled two feet down with the connector end laying in a small pool of water. I removed the other end of that hose from regulator and noticed water. Blew through the hose and it was full of water. The water in the pool had travelled two feet up the hose, entered the regulator and was deposited somewhere, maybe in a dip in the rubber hose, inside the RVís fuel supply line.

    This is a 44 foot trailer permanently in one spot. The supply line obviously had to be drained but unfortunately connection was so close to ground under trailer I couldnít get at it. Going to have to blow it out or use something that gets rid of the water.

    Anyways, I was surprised that water made the journey up that 3/8Ē outside diameter rubber hose. With no other source of water I concluded it was capillary action. Was I correct? Is there a certain diameter of hose/pipe/tube where that canít happen?


    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
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    In a tube of 3/8" diameter it can't be capillary action. The maximum vertical height capillary action can raise a water level is given by 2T/rpg where T is the coefficient of surface tension, r is the radius of the tube, p is the density of the liquid and g the acceleration due to gravity.

    For water T = 0.075 N/m
    Density = 1000 kg/me
    g = 10 m/s2
    r = 0.005 m approx

    So the height will be (2 x 0.075)/(0.005 x 1000 x 10) = 0.003 m or 3 mm!

    2 feet can't be capillary action. It's more likely that a pressure differential somehow developed (the temperature of different parts of the tubing changing by different amounts could do it if there is gas in the tube). This difference in pressure could suck water up the tubing.


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  4. #3  
    Time Lord zinjanthropos's Avatar
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    Quote Originally Posted by PhDemon View Post
    In a tube of 3/8" diameter it can't be capillary action. The maximum vertical height capillary action cannot a water level is given by 2T/rpg where T is the coefficient of surface tension, r is the radius of the tube, p is the density of the liquid and g the acceleration due to gravity.

    For water T = 0.075 N/m
    Density = 1000 kg/me
    g = 10 m/sr = 0.01 m approx

    So the height will be (2 x 0.075)/(0.01 x 1000 x 10) = 0.0015 m or 1.5 mm!

    2 feet can't be capillary action. It's more likely that a pressure differential somehow developed (the temperature of different parts of the tubing changing by different amounts could do it if there is gas in the tube). This difference in pressure could suck water up the tubing.
    Thought so. It’s a two way regulator, one side used at a time. I was thinking perhaps one side might be leaking thru to other even when other side off. Working pressure about 11” WC. The neoprene hose in question was 3/8” outside diameter so inside dia probably 1/4” . Would capillary action work for that size or residual (non flowing) gas pressure in main trailer supply line enough to draw water up? Could be small leak thru reg but still functioning. If I had a reg on me I would have changed it so told him to call service guy, I’m too old to be crawling around under trailer if I had to
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  5. #4  
    Bullshit Intolerant PhDemon's Avatar
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    Using 1/4" as the inside diameter would only change the height by a factor of around 3 to 6 mm. So it's more likely to be a pressure difference due to a leak or some other factor.

    (In your quote the calculation used the diameter not the radius, I've corrected the OP)
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  6. #5  
    Time Lord zinjanthropos's Avatar
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    Quote Originally Posted by PhDemon View Post
    Using 1/4" as the inside diameter would only change the height by a factor of around 3 to 6 mm. So it's more likely to be a pressure difference due to a leak or some other factor.

    (In your quote the calculation used the diameter not the radius, I've corrected the OP)
    The actual brass connector to the propane tank has a much smaller orifice. I’m not exactly sure of the size but it looks like 1/16” maybe slightly larger. In this case the connector was with point dangling in the water. Connector is 1 1/2 inches (approx) in length.

    Trying to word this properly.... can a small opening at one end draw water into a larger diameter tube and fill it to a point where can’t overcome gravity? On a lesser note: Can the material the hose is composed of affect adhesiveness of water molecule?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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  7. #6  
    exchemist
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    Quote Originally Posted by zinjanthropos View Post
    Quote Originally Posted by PhDemon View Post
    Using 1/4" as the inside diameter would only change the height by a factor of around 3 to 6 mm. So it's more likely to be a pressure difference due to a leak or some other factor.

    (In your quote the calculation used the diameter not the radius, I've corrected the OP)
    The actual brass connector to the propane tank has a much smaller orifice. Iím not exactly sure of the size but it looks like 1/16Ē maybe slightly larger. In this case the connector was with point dangling in the water. Connector is 1 1/2 inches (approx) in length.

    Trying to word this properly.... can a small opening at one end draw water into a larger diameter tube and fill it to a point where canít overcome gravity? On a lesser note: Can the material the hose is composed of affect adhesiveness of water molecule?
    Nah, I agree with PhDemon. I'm sure what you have is a mechanical/hydraulic issue, not anything to do with chemical affinity. It will be something like temperature cycling, probably. Or maybe a venturi suction effect if the gas flow from the tank was close to atmospheric pressure and the other branch was not fully sealed off, as it appears not have been if water got into the line.
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  8. #7  
    Bullshit Intolerant PhDemon's Avatar
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    Generally capillary action will only draw liquid up very thin bore tubing, once the diameter opens up capillary action stops.

    The main thing that causes capillary action is the attraction of water molecules to each other, the effect of tubing of different materials is negligible as far as I remember.
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