Propane Tank Pressure Gauge Meaning - SailNet Community
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post #1 of 19 Old 05-26-2008 Thread Starter
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Propane Tank Pressure Gauge Meaning

Last summer we bought an old boat that had a new stove and propane tank hookup, but no documentation. I did get stove info off the net

The small propane tank has a pressure gauge that goes from under 100 something to over 300 something (only looked at it briefy). Brifely, what is the gauge measuring and what would you think the pressure would read if it is getting near empty?

(We took the tank for our backyard grill tank in onetime to be refilled, and the serviceman said he desired it to be empty before he refills it.)

One option is that as a backup I carry some food which needs no cooking......but I am hoping you sailnet gurus will put me on the path of enlightenment.

Thank you for your time, SaltyPat
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post #2 of 19 Old 05-27-2008
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There is no reliable way to measure propane quantity, except by weigh. LPG remain liquid under pressure, so only the dry part of your tank is full of gas at almost constant pressure; as you liberate the gas, the liquid surface replace it transforming from liquid to gas;what is reduced is the liquid part, so your pressure gauge will read the same for a long time, and when it drops, indicate your tank is out of LPG. Too late. The gauge could help you detect leaks, at most.
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post #3 of 19 Old 05-27-2008
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Yes... you have to weigh it. The guage means next to nothing. It tells you there is some LPG in the tank, but not how much.
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post #4 of 19 Old 05-27-2008
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Quote:
Originally Posted by negrini View Post
The gauge could help you detect leaks, at most.
That's about all it does.
A drop in pressure over a period of time means you better get the soapy water out.

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post #5 of 19 Old 05-27-2008
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As long as there is liquid in the tank, the tank pressure will vary with the ambient temperature, not the amount of LPG in the tank. The liquid "boils" at a pressure that increases as the tank temperature increases.
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post #6 of 19 Old 05-27-2008
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Propane boils at -40 F, which is why they don't use it in real cold climates. That's how it gets it's pressure. You will have pressure right up until the gas is gone but it will fall slightly as the tank gets really low. Rises in temp will cause changes in pressure as well.
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post #7 of 19 Old 05-27-2008
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Salty Pat,

Suggest you review the thread below in the link. There is a lot of discussion in there about the purpose of the pressure gauge. It is a CRITICAL component of your propane system, but it does not measure the amount of LPG in the tank. It's sole purpose is for leak detection. As others have pointed out, remaining LPG is measured by weighing the tank:

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post #8 of 19 Old 05-27-2008
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SaltyPat,

I agree that there's no reliable way to know how much propane is left in the tank, except to weigh it. And, I believe a pressure guage is a good thing to help detect leaks.

But I believe that what most of us fear is running out of propane during a cruise, when there's not usually a filling station nearby. That actually happened to me a couple of years ago....ran out on the first day of a 5-day trip!

Now, I have a solution: I purchased a brass adapter which adapts the regular propane hose fitting (the one that screws onto your tank) to accept small propane bottles, such as are used in camp stoves, bar-b-que grills, etc. Boat US and West Marine have these adapters.

Then, I purchased two small propane bottles -- the squatty kind (Coleman, I believe) -- and built a mount for them next to the main propane tank. These little bottles are cheap, and will tide you over until you can find a place to refill the large tank.

Gotta have that coffee in the morning :-)

Bill

PS...find another place to refill your tank. Most places I've found will definitely fill a tank that's not empty yet. They simply place it on the scales, and fill it to the proper weight.

B.

Last edited by btrayfors; 05-27-2008 at 10:25 AM.
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post #9 of 19 Old 05-27-2008
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Below is an excerpt from an email that I sent the owner of a boat that I chartered. I think that it explains the meaning of the presure guage fairly well:

"When I picked up the boat, I noticed that one of the two propane tanks was low. I made this determination based on the weight of the tank. You probably know that at 70 deg F, at sea level, propane liquefies at 110 PSI. This means that at 70F the pressure gauge should never read higher than 110, but the weight of the tank will indicate how much liquid propane is contained in the tank. If the gauge reads less than 110, the contents of the tank have vaporized, and you will soon run out. In this case, the tank in question read 100.

While on this topic, the tank connectors require a 1.25" wrench. The adjustable in the tool kit only opens to 1". I brought a few of my own tools which included a large adjustable."

-Ed
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post #10 of 19 Old 05-27-2008
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Believe that you should have said: "This means that at 70 deg F the pressure gauge should never read LOWER than 110...." since if there is any amount of liquid propane, the pressure should be 110 PSI.
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Below is an excerpt from an email that I sent the owner of a boat that I chartered. I think that it explains the meaning of the presure guage fairly well:

"When I picked up the boat, I noticed that one of the two propane tanks was low. I made this determination based on the weight of the tank. You probably know that at 70 deg F, at sea level, propane liquefies at 110 PSI. This means that at 70F the pressure gauge should never read higher than 110, but the weight of the tank will indicate how much liquid propane is contained in the tank. If the gauge reads less than 110, the contents of the tank have vaporized, and you will soon run out. In this case, the tank in question read 100.

While on this topic, the tank connectors require a 1.25" wrench. The adjustable in the tool kit only opens to 1". I brought a few of my own tools which included a large adjustable."

-Ed

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