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Old 09-14-2010, 04:58 PM   #1
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doesn't all gas get sucked out?

My husband just returned from filling the tanks. I don't think our regulator works cause while I was out, I had to manually switch the tanks when my water heater wouldn't ignite and my refer was trying to fire up and couldn't. So manually switched the tank. Fired right up. When hubby got home he said the tank wasn't completely empty. Sooooooooooooo, my question, is it common that when the gas gets to a certain level that the appliances can't suck up that gas?
Thanx all brilliant ones.
PS We also will have to update our tanks also.
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Old 09-14-2010, 05:40 PM   #2
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Your appliances received gas which is fed by pressure. The liquid propane turns to a gas at the upper reaches of the tank. The regulator keeps too much pressure from feeding into the gas lines. Once the liquid falls below a certain level, the remaining liquid gas that is vaporized falls too low to maintain a flame on the appliance. If both tanks have their valves open, the regulator should sense the low pressure situation in the near empty tank and switch over to the full tank. That's assuming you have a properly functioning two way valve and again, you have valves open on each tank. Assuming the valves were open and you could not support a flame, my guess is that your regulator might be defective.

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Old 09-14-2010, 05:53 PM   #3
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Well, for what its worth here's my take! I'm sure there are folks here that know more about propane that I and hopefully they will comment.


Firstly, propane in your tank is stored in liquid form. There is space at the top of the tank and some of the liquid evaporates to fill the space with gaseous propane - it develops a pressure called the "Vapour pressure" and that pressure is dependent on whatever the ambient temperature is.

So your appliances don't "suck" the gas out, it is forced out by the pressure in the tank. As gas is removed, more will "boil" off the liquid propane in an attempt to reach the vapour pressure, and that gas will continue to operate your appliances.

The pressure in your tank is much higher than in your lines - as i said, it depends on the ambient temperature but can easily be over 100 psi.

The purpose of the regulator is to reduce the pressure to a much lower level - less than one psi - to feed the distribution system and appliances in your trailer.

As long as there is any amount of liquid propane left in your tanks, this situation remains the same and your appliances should work.

The vapour pressure in the tank should be the same with a tank that is full or, lets say, three quarters empty.

Once the liquid propane has all boiled off to become vapour, pressure will drop quickly in the tank as you draw the remaining gas off.

It is at this point that the automatic changeover valve should flip over and start drawing from the second bottle - as long as you have the bottle valve open on the second bottle!!

I'm assuming that you did have both bottles open at the outset and didn't just get things going again by opening a full bottle that was connected but left with its valve closed!

As far as I always understood, all that the manual flipper does is to reset the sight glass indicator from red back to white, and point to whichever bottle is providing gas so you know which one needs refilling.

Perhaps it is possible that if an auto changeover valve is defective - manually flipping the lever will cause the auto valve to change over even if it is defective and won't change on its own. If so, i was not aware of that feature.

Maybe I am missing something and someone who knows more will comment and I will learn something too!


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Old 09-14-2010, 06:00 PM   #4
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We figger we need a new regulator anyway. It hasn't switched before in the middle of use on our real cold outing.
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Old 09-14-2010, 07:53 PM   #5
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In my experience the regulator and tanks don't always perform according to theory. They can test out fine in the shop and occasionally fail to perform in the field - even when new.
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Old 09-14-2010, 08:35 PM   #6
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The boiling point of Butane is .5 degrees Celsius, right around the freezing point. The boiling point of Propane is much colder, -51C.

LPG or liquid petroleum gas, is a mixture of the two. If there was a lot of butane in the mix perhaps it wasn't vaporizing very well due to the cold, resulting in low pressure?

They use more butane in the mix in hotter climates in the summer. If you last got the tank filled in the summer, especially if it was in Texas or Arizona or New Mexico maybe it had too much butane to vaporize in freezing weather.

To test this theory you could try the tank again on a warm sunny day or pour some hot water over it.

It's also worth keeping in mind that as the gas evaporates it chills the tank. So the more you use the colder it gets. This could have the effect of dropping the temp below the boiling point, if it was already cold and had a lot of butane in it.

If the weather is getting cold your LPG supplier should have changed over to a more propane rich mixture. Get the tank filled and it should be fine from now on.
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Old 09-14-2010, 09:09 PM   #7
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Hey neighbor! Maybe your tank was just almost not quite completely empty. Do you go over to the Silver City RV? They're pretty nice folks there.
Hey plan on coming down to the Genoa Candy Dance fair the 25-26. If you're bored tomorrow, they're still making some candy in the town kitchen and love all the volunteers that show up, I hope to get over there in the afternoon or evening.
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Old 09-15-2010, 04:08 AM   #8
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Sometimes , but not often ours (regulator) has somehow stuck and we have tapped on it with the handle of a screww driver. When the propane runs out, you can smell it, as far as going on when you think it has run out.
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Old 09-15-2010, 04:52 AM   #9
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If your regulator is 20yrs old I would replace it. I replaced my $49 automatic switchover Marshall 205 and put on the optional $1.50 cover, works great and gave me peace of mind.
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