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Old 02-21-2015, 08:41 AM   #29
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You are correct in that the pressure relief valve is set

Vapor pressure in the tank is 287 PSIG at 130 deg F. per this:

Propane Regulator Facts , High pressure and low pressure propane , propane 101

or

315 PSI per this:

Propane Regulator Facts , High pressure and low pressure propane , propane 101

I probably read the storage tank working rating instead of normal pressure.
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Old 02-21-2015, 11:04 AM   #30
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Thank you, wa8yxm. Another voice of reason.

If it driped, why would liquid NOT come out of the 80% vent, instead of vapor?

It turns to vapor, instantly, above - 40 degrees.

Propane works like freon, extrating heat.

At one time, there were propane based products, used in central air systems to replace r22. Great until it leaks. It may still be around.

Anybody can test this, be it real dangerous, turn your 20 lb tank over, on plywood and crack the vent screw. Look for a puddle of propane.

Nice day
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Old 02-21-2015, 11:26 AM   #31
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Wow, talk about a little bit of information being dangerous; everyone here is right AND wrong to a certain extent. For my point of reference, I have a background in refrigeration and have been associated with the industry for over 40 years.

Most compounds with a boiling point below standard atmospheric temperature and pressure will exhibit the same properties to a relative extent. Because they exist as a gas under our conditions they can only be a liquid if the pressure is high enough (think a closed bottle of propane or freon) or if the temperature is low enough. If you were to have a pinhole leak in a high pressure line carrying either propane or refrigerant the results would probably be that initially gas would escape. If the leak got larger, or if it lasted long enough, it would cool the surrounding environment down to a point where it could now escape as a liquid, flashing into a gas only as it warmed up. This is where you could see a drip that immediately disappears. If the leak were large enough, you could actually shoot a column of super cold liquid! That is exactly what is done in medical procedures where they burn off warts with liquid nitrogen.
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Old 02-21-2015, 12:10 PM   #32
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But would the drips land on the ground, to be pointed out by a gas jocky.

And in the large leak, would there not be a LARGE vapor cloud?

Still standing
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Old 02-21-2015, 12:19 PM   #33
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Quote:
Originally Posted by twinboat View Post
But would the drips land on the ground, to be pointed out by a gas jocky.

And in the large leak, would there not be a LARGE vapor cloud?

Still standing
If the leak was large enough, as the propane escaped and cooled the point of the leak, it could also cool itself to last long enough to form a drip which could hit the ground, but it would boil off instantly as soon as it did. With a large leak, there could be a vapor cloud, but the cloud is actually frozen moisture, not gaseous propane, which is clear.


This demo shows how liquid nitrogen can easily exist in a cup because the cup is -320 degrees. The fog that you see in not nitrogen gas, but again frozen moisture.

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Old 02-21-2015, 12:29 PM   #34
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Propane loading facility where I work.........I could show the non-believers liquid propane dripping from a 3" loading line filling a 9k/gallon semi or 30k/gallon railroad car..........I have seen on a humid/rainy day, propane drip, and a ice build up where it is dripping freezing the moisture/rain.You ought to see the build up from leaking butane/iso butane while loading........
I have seen liquid propane puked out on the ground after a transport has been loaded and not properly vented/relieved to the flare system........
Here is the facility, you can see 3 RR cars spotted at the loading rack, no transports loading in the photo though.......count the "Bullet's" 30k each!
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Old 02-21-2015, 03:34 PM   #35
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Just wanted to add support to the "dripping" crowd. Many years ago on my first class C I was having my LPG tank filled and when the jockey completed the fill and removed his fill hose the check valve in my fill connection sprung a major leak. LP came out as a liquid and dripped to the ground, most of it vaporized as it was dripping but we did end up with actual liquid hitting the pavement. We were very fortunate that there was no spark or other source of ignition present as the whole tank leaked out before the technician could replace the faulty fill valve and refill the tank.
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Old 02-21-2015, 03:54 PM   #36
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I learned about liquid after being shown how to change a fill valve. We had to do several of them a season is SW Mi. as the salt, along with rare usage, would corrode them to the point they were difficult, if not impossible to shut off. This coming to light often when an appliance inside needed work.

You can't always wait for a tank to "empty" prior to changing the valve. In those cases where you could not for practical reasons, this meant "freezing the tank down". You would remove the POL/regulator, then open the valve (if it wasn't already), and walk away for a while. After a period of time, the big noise of the gas escaping would subside to a whisper/next to nothing, and it was time to go to work. The tank would be super cold, covered completely by a thick coating of frost! Cold enough where the remaining propane inside would no longer evaporate. You would then carefully remove the valve, being very careful of LIQUID pouring out of the tank as you removed it. If liquid propane was present at this point, not only did it pour out, but it would often splash - and that's what would usually get you.

Yes proper cautions were used. Wind direction, and what was downwind, as well as all batteries disconnected prior.
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Old 02-21-2015, 05:04 PM   #37
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Quote:
Originally Posted by palehorse89 View Post
Propane loading facility where I work.........I could show the non-believers liquid propane dripping from a 3" loading line filling a 9k/gallon semi or 30k/gallon railroad car..........I have seen on a humid/rainy day, propane drip, and a ice build up where it is dripping freezing the moisture/rain.You ought to see the build up from leaking butane/iso butane while loading........
This is good, an eye witness I can question.

First, I do admit if you make a hole big enough yes you can drip liquid propane,, But...

When you saw it dripping did a vapor cloud form around the leak,, Did the leak ice over, Was there a vapor cloud around the puddle on the ground?

Actually, these questions are important and will affect my position on leaks.

But every leak I've seen is like the Visual Overfill Indicator Valve (80% valve) I have seen it spit liquid, but never did a drop hit the ground, turned to vapor first. Large white cloud.
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Old 02-21-2015, 07:07 PM   #38
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I'd say it's going to depend on the temp of the liquid. The warmer it is when it appears, the quicker it's going to evaporate. If it's as cold as the stuff coming from the tank I was talking about above (while changing the valve) you'll see a puddle form (assuming there's enough in the tank to flow out the hole the valve normally occupies). When it stops pouring out, the puddle will disappear very quickly, leaving an obviously really cold (frosty) spot on the ground where the puddle used to be.
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Old 02-21-2015, 07:38 PM   #39
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LP at atmospheric pressure is a -44F liquid If you don't think so try pulling the valve out of a tank. I have poured LP out of a tank on a hot day in July and yes it was all liquid. LP is always filled in liquid form so any leaks in the filling process are liquid. Yes depending on temp it will evap very fast that however will still be cold and the vapor will be frozen water vapor that frozen water vapor will land and then warm up and become water once again leaving a puddle. So once again any leak in the filling process will be liquid how that liquid reacts will depend entirely on the temp and conditions at the time and place of the leak. The other day at 14below it stayed liquid for several minutes.
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Old 02-21-2015, 08:05 PM   #40
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Quote:
Originally Posted by wa8yxm View Post
This is good, an eye witness I can question.

First, I do admit if you make a hole big enough yes you can drip liquid propane,, But...

When you saw it dripping did a vapor cloud form around the leak,, No Did the leak ice over Sometimes when it was raining, Was there a vapor cloud around the puddle on the ground? No, not from a drip, raw,liquid propane will turn to a vapor
Weather conditions, temperature, humidity, rain, all are a factor.......

Actually, these questions are important and will affect my position on leaks.

But every leak I've seen is like the Visual Overfill Indicator Valve (80% valve) I have seen it spit liquid, but never did a drop hit the ground, turned to vapor first. Large white cloud.
Answer's in bold above in quote.....
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