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Old 08-16-2011, 02:29 PM   #1
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PROPANE TANK GAUGE ACCURACY

Recently had a certified propane system inspector perform an annual check of my SMB propane system. No leaks. Water column at 11.8" (need 11") - good. When asked, the inspector said propane tank gauges are "pretty accurate" - even though these gauges can't be used by service personnel when filling your propane tank.

I was wondering if others would share their own experience with propane gauge accuracy. My gage consistently reads 1/2 full, but then it only reads 3/4 full when the service attendant fills it up with two gallons and says it's full. It's a ten gallon tank. Full would be 8 gallons. So half full is 4 gallons and 2 more doesn't add up to 8...

What gives?
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Old 08-16-2011, 03:21 PM   #2
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Re: PROPANE TANK GAUGE ACCURACY

I've found they are more of a three-position guage -
1. really full
2. has some
3. dang near empty

There is actually a float inside the tank and due to the horizontal cylinder shape the level stays around 50 percent +/- over a large range of volume. The level indication and also the fill level would be affected by how level the tank is sitting.
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Old 08-16-2011, 04:01 PM   #3
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Re: PROPANE TANK GAUGE ACCURACY

They can't/shouldn't fill more than about 3/4 by design- it allows for expansion. So your gauge is accurate in that respect. If you ever read full after a fill you should seriously question the process. Unfortunately a lot of untrained attendants who are convinced they know everything out there.

Another tip from the same RV shop I learned the above from- don't ever let it go to zero. Once it's at zero the guy manning the pump doesn't know if that's because you have a leak or because you ran it out. Most would blindly pump it full of propane and send you on your way, but he said they might refuse to fill without a full inspection. (wherein you just move on down the road...)

As far as my gauge, I apparently don't use propane enough to know, notice (or care) about it apart from "Yup, still don't need to refill"
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Old 08-18-2011, 07:16 PM   #4
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Re: PROPANE TANK GAUGE ACCURACY

I just installed an older (18 years) tank in my van several weeks ago.Its a 7.9 gallon tank.My local station filled the tank and of course the gauge does not work This is the least of my trouble Last week i decided to go to Nv. and while driving through Stockton at 101 Deg. the tank started venting only for several seconds at a time maybe 5 time. I figured It would be best to speed up rather than to pull over!!!! Anyways It concern me that the attendant who filled the tank stopped filling when the bleed valve starter venting liquid, then added another .2 gallons!! Not sure what to do drop the tank and get a new valve and gauge or just live with it. Sorry about the high jack but it kinda related .

Dave
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Old 08-18-2011, 08:29 PM   #5
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Re: PROPANE TANK GAUGE ACCURACY

So, the attendant filled your tank up until your tank's relief valve spilled propane? Sounds like a disaster waiting to happen, like last month's van explosion and fire (totaled the van) at a Seattle, Washington propane filling station. Still don't know what caused that.

My gage was at the 1/2 mark before my RV dealer's propane attendant was able to get 2 gallons in, and now it reads as shown on the photo below - at less than 3/4. Since I have a ten gallon (water volume) tank which is rated for 8 gallons of propane, am I to assume the redline area on the gage is the 80% level of the tank by water volume? This would account for the required safety margin (don't know where the 3/4 level comes into play Jage - I never heard of it). BTW, thanks Jage for the tip on avoiding reaching an empty tank - that makes good sense.

When I asked the attendant if my tank was full, given the gage reading - and qualifying that I understood he was not allowed to use any gages other than his own - he blew off 0.2 gallons of propane out his service tank vent. This vent is located about 10' in the air (a few feet above the propane filling tank). Assuming their relief valve is set below the pressure my tank's relief valve is set at - and that mine is set to regulation - this meant he couldn't fill my tank any further.

[photo][/photo]
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Gage for Full Propane Tank.JPG  
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Old 08-19-2011, 07:28 AM   #6
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Re: PROPANE TANK GAUGE ACCURACY

Quote:
Originally Posted by unimogdave
Anyways It concern me that the attendant who filled the tank stopped filling when the bleed valve starter venting liquid, then added another .2 gallons!!

Dave
If you can get to the bleed valve, open it up and vent propane until the liquid stops coming out. If the tank is over full, which it is, you run the risk of drawing liquid propane into your appliance rather then gas. This is NOT a good thing. I wouldn't use any propane appliance until you vent off the tank.
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Old 08-19-2011, 09:12 AM   #7
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Re: PROPANE TANK GAUGE ACCURACY

Everytime I've had my tank filled, the attendant stopped when liquid came out the bleed valve. Seems to be normal procedure, from Alaska to California to Florida.

And everytime, my gauge is right at 3/4 tank.

Mike
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Old 08-19-2011, 07:10 PM   #8
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Re: PROPANE TANK GAUGE ACCURACY

Quote:
Originally Posted by Ford_6L_E350
Everytime I've had my tank filled, the attendant stopped when liquid came out the bleed valve. Seems to be normal procedure, from Alaska to California to Florida.

And everytime, my gauge is right at 3/4 tank.
Ditto- exactly what I've experienced.
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Old 08-19-2011, 07:45 PM   #9
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Re: PROPANE TANK GAUGE ACCURACY

Scatter I did not think to do that(bleed gas off) I ended up turning the water heater on and ended up dumping 15 gallon of hot water on the ground . Dave
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Old 08-20-2011, 05:29 AM   #10
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Re: PROPANE TANK GAUGE ACCURACY

I was a licenced propane plant operator way back so I'll throw in my two cents.

The only legal thing to use for a full indication is the "spitter" valve. The gauges are notoriously inaccurate. Also note the diameter of the gauge. The smaller the diameter the less accurate they are.

The temperature and mixture percentages on the gauge face also need noting. Generally we get a mix of propane, butane, and maybe some ethane in our propane fill. If you read the inner scale in small black letters near the 100 mark you'll note the three ranges for each of three mixtures. Our propane is so close to 100% pure that the innermost scale would be appropriate. That said note the temperature difference versus percentage full as temperature rises.

The reason for 80% as full are numerous. Expansion is one, but mostly it's to allow a cloud of vapour to accumulate above the liquid. As noted by Scatter you don't want liquid propane at the burner. The vapour is what mixes with air to provide the fuel. The ratio of liquid to it's vapour state is in the order of 270 times so the liquid is a potent way to store propane.

The gas state of propane is much heavier than air so it will sink into low spots and stay there waiting for a source of combustion. This is a note to owners of below floor storage areas and grease pit inspection facilities. Tagging off when using a ferry is the only way to travel with propane. Underground parking, not that the big Sportys would fit, is also forbidden.

It is non toxic although the liquid at the spitter valve can give you quite a frosty burn. Octane rating is well above 100. No cylinder dilution of oil issues when burned as a motor fuel. Used motor oil from a propane burning engine is very clean looking because there is less carbon in propane than in gasoline.

Lastly you can carry it around in a regular bucket if you're lucky. Lucky enough to be outside at a temperature of -40 degrees or so.

Regards,

Gavin
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