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Regulator's pressure meter of 15 ltr. LP gas cylinder showing RED!!!

Discussion in 'Renewable Energy' started by Willen, Jun 10, 2018.

  1. Willen

    Willen Well-Known Member

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    While buying the regulator the seller just said red is danger, green is normal and yellow is low. When I used new cylinder today, it shows Red! What it means? The gas is more than a limit inside? Or there are some leakage? And what I need to do now?
     
  2. JimB

    JimB Super Moderator Most Helpful Member

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    Not enough information.

    Red yellow and green on the pressure gauge means nothing.
    What is the actual pressure (psi or Bar or ??)

    The pressure in an enclosed tank with liquid and gaseous propane will be mostly dependant on the temperature.
    There will be some variation depending on what other gasses are in there as well. (eg Butane, ethane , methane).

    Have a look at the graphs here:
    https://www.engineeringtoolbox.com/propane-vapor-pressure-d_1020.html

    Measure the temperature of your propane tank and read the actual pressure shown on the gauge on the regulator.
    Compare the readings with what is shown on the graph.

    Note that I am assuming that your LPG is propane and not butane.
    Also that the gauge on the regulator is scaled for the corrct gas.

    JimB
     
  3. unclejed613

    unclejed613 Well-Known Member

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    it depends on the way the gauge is meant to be used, is the gauge before (between the bottle and the regulator) or after the regulator, and is the red at the top of the scale (right side) or bottom of the scale (left side)?

    if the gauge is after the regulator, and the red is the top of the scale, you have the regulator set too high.

    if the gauge is before the regulator, maybe the bottle has been overfilled.

    when you buy gas, be absolutely positive about what you are buying. there is one flammable gas that should NEVER be filled overpressure, and that's acetylene. if acetylene is filled above 200PSI (13ATM), it can spontaneously detonate (yup, that triple valence carbon bond is unstable).
     
  4. dave miyares

    Dave New Member

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  5. Willen

    Willen Well-Known Member

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    Hi, The pressure level meter is a part of regulator (attached). The red means full of the scale and Yello is low scale and green for 50%. The meter do not have numbers about pressure unit. It was showing red (overpressure) two days ago which was pretty hot day (40 degree C). So I guessed because of high temperature. So I used water to cool down the cylinder few minute. Then meter dropped to green.

    Is it normal with LP gas?
     
  6. unclejed613

    unclejed613 Well-Known Member

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    yes, and that is fairly warm. keep the cylinder out of direct sunlight, and away from surfaces that radiate a lot of heat like asphalt road or parking lot surfaces. i'm guessing Nepal at this time of year is kind of a hot climate.
     
  7. Willen

    Willen Well-Known Member

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    I never have thought about storing temperature of the cylinder. Nepal has any type of climate always. I am living around 150km south from the tallest mountain Mt. Everest and here days are hotter like 38 to 40°C. Just 150km north in there is snowfall always.
     
  8. dave miyares

    Dave New Member

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  9. gophert

    gophert Active Member

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    Propane is mostly in the liquid state inside the tank. The space above the liquid is propane gas and the pressure of the gas is proportional to the temperature of the tank. A pressure gauge is not helpful for liquidified gases like propane. You must either weigh the tank or check the temperature of the tank from top to bottom to feel where it is cool (the surface of the liquid cools when propane evaporates - only works while gas is flowing out of the tank).
     
  10. Willen

    Willen Well-Known Member

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    Hi,
    And since the gas is liquid, how there's pressure created inside?

    Maybe gas above the liquid creates pressure but why there's liquid propane and gas propane both created in a same tank?
     
  11. JimB

    JimB Super Moderator Most Helpful Member

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    At room temperature and pressure (20 degC and 1 barA), propane is a gas.

    When the gas is compressed it becomes a liquid.

    When the liquid is contained in a sealed container, with free space above the liquid, the liquid will evaporate (boil) until a pressure equilibrium is reached.
    The pressure will depend on the temperature, the pressure/temperature relationship is given in the graphs which I linked in post#2.
    This pressure is known as the Vapour Pressure.
    Look at the second graph, at 20 degC, the pressure will be about 8 bar.


    JimB
     
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  12. large_ghostman

    large_ghostman Well-Known Member Most Helpful Member

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    Acetylene cylinders contain a honeycomb material and the acetylene is dissolved in acetone rather than as a compressed gas, precisely to stop them going bang if dropped. Modern ones the filler prevent over filling as the gas is mixed with a solvent.
     
  13. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Here is a bottle half full of liquid and half of gas. (well probably air which is CO2 and many things) The gas could be water vapor like a cloud. You can have water as a liquid and as a gas at the same temperature and pressure.
    [​IMG]
    Get a bottle with a vacuum in it. (nothing there, like space) Fill it 1/2 full of water. About 0.1% of the water will turn to gas to fill up the vacuum. Now you have a bottle with 49.1% liquid water and 50.1% water gas. By weight the bottle is 1/2 full. If you tried to put more liquid water in the bottle the more pressure will force some of the gas back to liquid. If you removed some of the water the reduced pressure will allow more liquid to move to gas.
     
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