Propane Tank Contents Level

[Dodge]

I eluded to this question on another thread but I thought I should make a topic specific post. How do you guys tell how much gas is in the tank. I know its probably pretty easy on the smaller tanks as I understand they frost up easily, and you can just pick them up and shake them. However, I have 100#er and it only gets frost on it in the warmest most humid times of the year and I try to not pick up 100 # objects very often (Yeah I know its not ALWAYS 100#) ; let alone shake them . Most of the time I can't tell by feeling it; especially this time of year. I thought about buying a cheap bathroom scale and just setting the tank on it but I don't know how accurate that would be or how it would hold up with the tank on it constantly. Any Ideas??
Thanks,
Scott

[DennisG]

Dodge, you can get guages for the tank, we have them on our tanks for our fork lifts, they work in the vert and horiz positions. Not sure the price but maybe check with your local propane supply company.

[pkrankow]

All tanks (are supposed to) have a tare weight marked on them. Use a scale appropriate to the tank size.

Phil

[maddog]

A bathroom scale is not very accurate of course and they get worse for small weights. I wouldn't use one to estimate the actual weight of propane in the tank, but they will show the difference as the tank empties which is probably all you need. And hey, you are gonna feel great when you see the pounds just melt away! :)

[CurlyGeorge]

Hey Scott. Ask Stan where he got the guages that we used on my tank. I think that he picked them up at Rural King, which is just a type of farm supply store. I have one for tank preasure and another for line preasure. :D

[CurlyGeorge]

Here's the set up for my tank, Scott.

[Wilson and Son]

I haven't tried this, but I've heard that you can see the level if you pour water on the side of the tank after it's been running for awhile. I keep forgetting to try it. Maybe tomorrow if I don't forget again....
Jeff
On the Wet side of Puget's Sound

[Dodge]

Here's the set up for my tank, Scott.

LOL Maddog. I can't wait to watch it disappear!!

Thanks Curly, I will probably do that. I didn't think my big tank would frost as I have never used it for the run times I have lately especially with the cooler temps, but the last couple days, as the tank gets below a third full it does get a frost map on it even when the outside temp was in the 40s. So I have learned that I'm not using gas as fast as I was afraid which I was becoming a worry, but with the addition of a tank gauge, I think it will be easier to determine the amount that is in the tank.
Thanks to all for all the input. I'm Starting to get into some more serious forging (folks do actually pay for this stuff sometimes! )and I'm starting to be more concerned about the amount of fuel (as well as materials of course) I'm using. It isn't just a toy anymore LOL

[Fosterob]

I am not sure that the high pressure gauge will tell you anything other than the tank has liquid in it. Same as a CO2 tank. If there is liquid in the tank to boil off it will always have the same pressure regardless of the level of the liquid. That is why propane tanks have a float in them to tell you how much is in it, like the fuel tank on your car. I am not sure what happens when the tank starts to freeze up? Is the liquid so cold that it no longer boils off into gas? In which case the pressure gauge will read empty when the tank just has cold liquid in it? Check me on this but I think it is right.
Rob

[peacock]

Fosterob you are correct. the guage will not tell you volume of the tank. every tank has a tare wt. stamped on it. Make a simple scale out of a picec of tubing with 3 holes. drill one hole near each end, drill a hole betwwen the 2 end holes with a ratio of 10 to 1. hang it up by the middle hole, hang the tank on the short side, hang a weight 1/10 of the tare weight on the other hole, it should come close to balance. Now as you use the gas you can pull down on the long end to get an idea how much gas is left. If you add about one pound of weight to the long end the tank will come off the floor with about 2 gal. of gas left.

P.S. ioo# tanks tare weight run from 64 to 72 (about) depends on when they were made.

[Bryce Masuk]

just look at the frost line

if its about 3/4 of the way up its totally full, once the line is near the bottom its time to refill

either that or tap the tank

[CurlyGeorge]

You guys may very well be correct on the tank preasure guage. I am a total rookie when it comes to gassers. Thanks for all of the interest and the tips. :D

[CurlyGeorge]

OK. I've got another tank on standby, now. Just in case. :D

[Nakedanvil - Grant Sarver]

Reminds me of one time in Las Vegas. I ordered a beer and as I sat there I said "that's not cold"! Well, it had no condensation on it. It was cold, but there is no moisture in the air there. So, anyone here from desert country? Does your propane tank frost up?

[petere76]

Gents,

Its weight not volume. You fill the small tanks by weight. Thats why they refer to them as 20 pounders.

Peter

[Nakedanvil - Grant Sarver]

Gents,

Its weight not volume. You fill the small tanks by weight. Thats why they refer to them as 20 pounders.

Peter

And yet when I purchase propane, they sell it to me by the gallon (volume) not by the pound (weight). There's a direct relationship between the two.

[fciron]

Gents,

Its weight not volume. You fill the small tanks by weight. Thats why they refer to them as 20 pounders.

Peter

So I don't have to worry about it being empty when I see the frost line is only a couple inches from the bottom? :blink:

[petere76]

Grant,

Bulk delivery is by the gallon as is bulk storage gauging. Bulk Propane is sold by the gallon for pricing purposes.

However, In the small bottles you see on BBQ and use in the forge, they charge them by weight, hence the tare weight on the containe, so you can calculate the weigh of the gas. If you go to an old filling station you will see the scale with the sliding weights. All the new bottles have OPDs which is essentially a float swich that (hopefully) prevents over filling.

The science is a Pressure volume relationship, expressed as the formula ((P1xV1) = (P2XV2)), The Temp varient is consider constant. I believe it Boyles and Mariotes equation also called the ideal gas law. Dont quote me I'm sure if passed that course.

A saturated liquid (LPG under pressure) has one volume for its liquid state and a much larger volume for its expanded or semi-expanded state. Its stored as a liquid but used as a vapor. Thus if you overfill the bottle and then it gets warm...the relieve valve or rupture disc will let go. lacking either of those items the container will fail. The weight of the container notwithstanding, when the tank is empty you should be very close to the tare weight of the container.

LNG (natural gas off oil wells) is transported as a compressed and sub cooled liquid. This is how ships transport LNG, its refrigerated to keep it in the liquid state. At the discharge port the liquid is re-gassed and stored in the large tanks you see in cities.

Hope that helps...I think its miller time.

Peter

[Nakedanvil - Grant Sarver]

No, I don't use bulk anymore. When I take my small tanks down to be filled I pay $2.45 per gallon. Expansion: Same thing will happen with the fuel tank on your car.

[fciron]

No, I don't use bulk anymore. When I take my small tanks down to be filled I pay $2.45 per gallon. Expansion: Same thing will happen with the fuel tank on your car.

In addition, multiple folks have already pointed out the possibility of weighing tanks to see how they're doing.

It ain't quite rocket science.

[Dave Budd]

not very scientific and not totally accurate, but I just knock the tank with my knuckle and listen to the sound it makes. Almost empty tanks sound very different to almost full ones and I normally have an empty around somewhere for a comparison ;)

[calala]

Hi all, just have a full bottle on standby, when bottle "a" runs out hook-up bottle "b" and refill bottle "a", you will stop your hair falling out from scratching your head. :)

[Frosty]

Propane = 4lbs./gl.

Frosty the Lucky.

[Wilson and Son]

Fill by weight. Interesting. The local Coop where I get both 20 and 100 lb tanks filled has never weighed any of my tanks. Usually fill the 100 where it sits tied in the back of the truck. When the white cloud begins to escape from the vent, it's full. I've never had a tank relief valve pop.
Just thinking...
How would they weigh the 20lb tank permanently mounted under the neighbors camper?


Didn't light the forge today so I didn't try pouring water on the tank.

Jeff
On the Wet side of Puget's Sound. High of 38 deg. today.

[maddog]

I live in the high desert. My tanks frost up but its only a light coat and isnt visible till the pressure has already plummeted.

Propane like water has a nearly constant density so measuring it by weight or volume are equivalent.

As Petere explained, if there is any liquid in the tank, the space above will be at the vapor pressure for propane at that temperature. Vaporizing propane requires energy which it gets by sucking heat out of the liquid. As it cools, the vapor pressure eventually drops below what the regulator is trying to draw and you cant run your forge any more.

Oxygen cannot be liquified at any practical temperature with pressure. Which is why, to get a useful quantity of oxygen into a tank, it has to be compressed to frighteningly high pressure. With an oxy tank, tank pressure is a useful way to measure how much is in the tank, since there is no liquid involved.

I think weight or observation of the dew line are the only useful ways to estimate the contents of a propane tank. I guess tapping works if you only need to know empty or not. Im going to buy a bathroom scale next time I go to the thrift store.


There is no bulk refiller anymore in my town. I take six 20lb tanks and one 40lb tank to the next town to fill all at one time. They weigh the tank as it fills and I pay only for the actual weight that they pump in. I guess if you cant weigh the tank and just fill it till it backs up, you get charged for a full tank regardless of what you had in there.


I hate going down the highway with all that propane in my PU bed. I also hate storing that much propane near my house. When we had a big fire in 00, the propane tanks were like bombs. I've toyed with the idea of using gasoline. I can get gas 24/7 just up the road. I would only need to keep a small amount on hand.