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Old 12-01-2016, 15:31   #1
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Propane cylinder, size matters?

I have a propane heater that works really well. The problem is that I ran out of full 30lb cylinders and hooked up a 15 lb. It will not stay lit. I know the gas is good and the cylinder has gas in it. I hooked it up when full and the heater worked for a couple of hours then went out. I can relight but it goes out after a short time.
Can anyone explain to me what is going on?
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Old 12-01-2016, 15:52   #2
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Re: Propane cylinder, size matters?

A fleabeesnoight in the jet or regulator...some contaminant partially blocking flow...to a lesser unlikely degree the regulator...
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Old 12-01-2016, 16:13   #3
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Re: Propane cylinder, size matters?

Are you sure of the orientation of
the internal pickup?
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Old 12-01-2016, 18:34   #4
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Re: Propane cylinder, size matters?

Quote:
Originally Posted by Freemind View Post
I have a propane heater that works really well. The problem is that I ran out of full 30lb cylinders and hooked up a 15 lb. It will not stay lit. I know the gas is good and the cylinder has gas in it. I hooked it up when full and the heater worked for a couple of hours then went out. I can relight but it goes out after a short time.
Can anyone explain to me what is going on?
You may be experiencing reduced 'vapor pressure' in the smaller tank if the tank is cold either due to ambient temperature where it is stored, or due to high volume of gas discharge... This is especially true if the larger tanks had no issues n the same conditions.

Basically this means less liquid propane is evaporating within the tank due to the temp of the tank and the small surface area of the liquid in the smaller diameter tank. Therefore, pressure in the tank is reduced.

Are you seeing frost build-up on the tank? That is a sure sign, but doesn't have to be present... [We have all seen this on a hot summer day using 1# canisters on a portable BBQ... once it ices up the pressure reduces and the burner flame keeps getting lower...]

If this is the case, it is time to get those larger tanks filled... or keep pouring warm water on the smaller tank. [Which is also a reasonable test for reduced vapor pressure... If the heater works normally for a few minutes after the warm water treatment, you have confirmation...]

If it is cold, you may also have a frozen regulator. Make sure the vent on the regulator is pointing down so condensation can drip out instead of accumulate and freeze. If not frozen, then you may have a flow problem either at the tank connector, pressure regulator, or heater controls.

e.g., At about 20F our [full] 20# BBQ tanks start to exhibit lower pressure at the burners... until we hit about 5F when the 20# tank is virtually useless. A 50 or 100# tank will work well at those temps, however.

This is why you see rather large horizontal propane tanks at business and residences in cooler climates. The larger the tank, the less it is affected by reduced vapor pressure.

Best wishes getting that heater back to normal.

Cheers!

Bill
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Old 13-01-2016, 09:32   #5
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Re: Propane cylinder, size matters?

Quote:
Originally Posted by wrwakefield View Post
You may be experiencing reduced 'vapor pressure' in the smaller tank if the tank is cold either due to ambient temperature where it is stored, or due to high volume of gas discharge... This is especially true if the larger tanks had no issues n the same conditions.

Basically this means less liquid propane is evaporating within the tank due to the temp of the tank and the small surface area of the liquid in the smaller diameter tank. Therefore, pressure in the tank is reduced.

Are you seeing frost build-up on the tank? That is a sure sign, but doesn't have to be present... [We have all seen this on a hot summer day using 1# canisters on a portable BBQ... once it ices up the pressure reduces and the burner flame keeps getting lower...]

If this is the case, it is time to get those larger tanks filled... or keep pouring warm water on the smaller tank. [Which is also a reasonable test for reduced vapor pressure... If the heater works normally for a few minutes after the warm water treatment, you have confirmation...]

If it is cold, you may also have a frozen regulator. Make sure the vent on the regulator is pointing down so condensation can drip out instead of accumulate and freeze. If not frozen, then you may have a flow problem either at the tank connector, pressure regulator, or heater controls.

e.g., At about 20F our [full] 20# BBQ tanks start to exhibit lower pressure at the burners... until we hit about 5F when the 20# tank is virtually useless. A 50 or 100# tank will work well at those temps, however.

This is why you see rather large horizontal propane tanks at business and residences in cooler climates. The larger the tank, the less it is affected by reduced vapor pressure.

Best wishes getting that heater back to normal.

Cheers!

Bill
Thanks Bill,
I was thinking there had to be a reason that only the larger tanks worked, but I really wanted to understand why.
Thanks to all who replied also. You can never have too much knowledge in the old "noggin".
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Old 13-01-2016, 11:56   #6
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Re: Propane cylinder, size matters?

I've been using 1# bottles as a temporary supply when the big tank runs out in the middle of cooking supper. They have been effective at -5C with no noticeable loss of heat in the oven, stove top or demand heater.

I suspect you have a small restriction somewhere unless it's colder where you are or your heater sucks a lot of propane very fast.
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Old 13-01-2016, 12:42   #7
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Re: Propane cylinder, size matters?

Yes almost certainly you are freezing the tank. If it is less than 10deg C consider also check they did not give you butane instead of propane, many smaller tanks are butane filled and it has much greater freezing issues (but cheaper and fine for summer)
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Old 13-01-2016, 12:56   #8
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Re: Propane cylinder, size matters?

What Mr. Wakefield and Roland said, not enough surface area on the smaller tank to keep the LPG evaporation going. It takes ~170BTU/lb (~700BTU/gallon) to evaporate the LPG in the tank. You should get around 21000 BTU/lb burning the LPG, so if you can duct a little bit of the heat from your heater back to the tank to help keep the tank warm you should be able to run on the smaller tank (if you really can't get the bigger one filled again). If it is sunny but cold, you can also put the tank in the sun in a dark plastic bag to get it some extra heat.
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Old 13-01-2016, 13:38   #9
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Re: Propane cylinder, size matters?

With great discretion and care:
Do you have electricity? Placing a SMALL low-temperature heating pad under the tank, and then draping some insulation or a blanket around it, may allow it to warm up enough to get the room warmer. At which point obviously shut the heating pad, unless you're going into the satellite launching business.(G)
A relatively safe kludge along those lines should be possible. "Kids, don't try this at home".
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Old 13-01-2016, 17:10   #10
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Talking Re: Propane cylinder, size matters?

Quote:
Originally Posted by hellosailor View Post
With great discretion and care:
Do you have electricity? Placing a SMALL low-temperature heating pad under the tank, and then draping some insulation or a blanket around it, may allow it to warm up enough to get the room warmer. At which point obviously shut the heating pad, unless you're going into the satellite launching business.(G)
A relatively safe kludge along those lines should be possible. "Kids, don't try this at home".
More probably the astronaut launching business. A dangerous game as the author suggests.
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Old 13-01-2016, 17:17   #11
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Re: Propane cylinder, size matters?

Well, if you want to get official and all, you can spend way too much money on a thermostatically controlled heating blanket for your tank. Avoids the astronaut scenario.

Heaters | Powerblanket | Powerblanket® Propane Gas Cylinder Insulated Electric Warming Blanket GCW20 20 Lb. Capacity | B226148 - GlobalIndustrial.com
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Old 13-01-2016, 17:59   #12
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Re: Propane cylinder, size matters?

There are also many "gentle" heating pads on the market, sold for use in photography trays, or in iguana tanks, or other purposes that most folks don't think of. Typically they are a silicon rubber matte with a heating wire embedded, and a maximum temperature that is so low you could place a bare hand or face on it all day and just be "warm".


And of course on the other hand, just pointing a 100-wat light bulb in a reflector has been used to keep many engines warm--without blowing them up either.


As Edison and his contemporaries argued, that electricity stuff, any kind of it, might just jump out of the socket and murder you in the night! Much safer to stick to coal gas, or whale oil. Much safer.
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Old 13-01-2016, 20:35   #13
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Re: Propane cylinder, size matters?

[QUOTE=hellosailor;2015221]There are also many "gentle" heating pads on the market, sold for use in photography trays, or in iguana tanks, or other purposes that most folks don't think of. Typically they are a silicon rubber matte with a heating wire embedded, and a maximum temperature that is so low you could place a bare hand or face on it all day and just be "warm".

Better to go back to Hello's earlier post on the subject that included the warnings, or stick to his/her quote above. Except in very desperate times, the risks of (over) heating a gas cylinder and the potential dire consequences of doing so are almost certainly are a bad choice.
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Old 14-01-2016, 20:18   #14
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Re: Propane cylinder, size matters?

Quote:
Originally Posted by jongleur View Post
Are you sure of the orientation of
the internal pickup?
This too is a good point. Some bottles are made for operating on their sides - others - upright. Internal safety devices may prevent gas discharge if the orientation is wrong.
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