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Old 11-02-2015, 08:10 PM   #15
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Question: Does the 30lb tanks hold 7 gallons or is it "about" 7 gallons?
Propane weighs about 4.3 pounds per gallon at 70F, so a 30-pound tank holds 7 gallons. But it really IS only "about" 7 gallons, because it also depends on what the temperature is that day. In colder temperatures you can fit more in the same cylinder before the OPD valve shuts off the flow. In warmer temperatures you might not quite get a full seven gallons before the OPD valve shuts off the flow.

If you look at the total volume of the 30-pound cylinder, if it was filled 100% full it would hold 8 gallons or 37 pounds of propane. So if you're getting seven gallons in a 30-pound cylinder, that's 80% of the total capacity, and you're good.

If the 30-pound cylinder is filled by weight rather than by volume, it should weigh 55 pounds when full, plus or minus about a pound.
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Old 11-02-2015, 08:31 PM   #16
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When I get my tanks filled they screw the fitting on the end of the fill hose onto the valve, open my tank valve and then open the lever valve on their fitting. Liquid propane flows into the tank and I assume the gas vents through the hose back to their large storage tank. When full shut all valves and unscrew fitting. They never touch anything else.
Sometimes they put the tank on a scale but with the new valves they usually trust the valve to stop fill at 80%
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Old 11-02-2015, 08:55 PM   #17
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Propane Bottle and LP Gas Cylinder Filling

Everyone that has filled my tanks opens the bleed valve. Why should they trust the OPD to work on every tank they fill and risk overfilling.

My valve isn't venting anymore.

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Old 11-02-2015, 08:58 PM   #18
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Fill stations may open the bleeder to speed up the fill but it is not necessary,, and yes I think the tank could be overfilled!

OPD Valves are usually triangular are they not?

Gallons vs weight there will be a variation due to temperature. The OPD simply shuts off the fill line internally once the liquid level is as high as is safe for the tank. Another point made to me a few years back is that vertical tanks must be transported in vertical position, since the rupture disc is sized for vapor relief. If the tank is on its side, the rupture disc is not large enough to vent liquid fast enough if the tank were for example over pressured due to a fire.
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Old 11-04-2015, 02:01 PM   #19
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The place where I get my propane also opens bleeder valve. It used to be known as the 80% valve and was the correct way to detect when to stop the fill. I've also had fills on the road and every place I've gone to in the past 10 years continues to use that method. Personally I'd rather have them for it that way.

I remember that before using that valve, some places filled by weight. After having a tank filled by weight alone vent on me, I always asked that the filler use the bleed valve rather than weight alone if I noticed that he didn't have a screw driver with him.

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Old 11-04-2015, 02:40 PM   #20
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My tank valves are triangular and show OPD displayed on the valve knobs.

I think the tech put the tank on a scale. I moved away because I had the dog with me so I didn't see everything he did. I got the propane at an RV park. I think I saw him use a screwdriver when starting the filling.

I should've run the trailer off this tank that night as the furnace was being used.

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Old 11-04-2015, 02:50 PM   #21
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There is a danger in using weight if your Airstream has aluminum tanks. While they put those tanks on a scale they are lighter than steel tanks, and filling to a specific weight can cause an overfill. I've seen this happen when guys are used to filling steel tanks. If you are filling by weight, you need to look at the collar of the tank which shows tank weights. That's why most folks use the valve method.
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Old 11-05-2015, 12:07 PM   #22
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Quote:
Originally Posted by jcanavera View Post
There is a danger in using weight if your Airstream has aluminum tanks. While they put those tanks on a scale they are lighter than steel tanks, and filling to a specific weight can cause an overfill. I've seen this happen when guys are used to filling steel tanks. If you are filling by weight, you need to look at the collar of the tank which shows tank weights. That's why most folks use the valve method.
I always look or ask to verify if the scale has been tared to my tank weight or set to total of my tank plus 30lbs... Can't be sure that last fill wasn't a 20 lb tank
If you have aluminum tanks it would be good to know the tare weight and remind the operator using a scale that he needs to either zero it with your tank on it, or adjust the trip to include your tank weight plus 30 Lbs
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Old 12-23-2017, 12:22 PM   #23
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Overfilled and boiling

Had one tank filled yesterday by a kid who knew nothing about the "bleeder" valve and fumbled around as if the whole thing was new to him: I should have insisted someone else do it. This morning it sounded like the propane in the tank was boiling and there was gas venting from the tank's vent tube. I called the retailer and was told that it was "impossible" to overfill a tank and that they "never" open the valve. He said that he had no clue why it would be venting. So, called another retailer who recommended opening the bleed valve, now, to release pressure then keep the tank out of the sun. So, I opened the valve, bled it for about 30 seconds--and the problem seems to be resolved. What do you think?
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Old 12-24-2017, 01:39 PM   #24
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The most recent fills I've been getting for my 40# aluminum tanks has been by volume and not by weight. A tank that feels empty to me will take just about 9.3 gal of propane. They always open the vent as the pump is coming to a stop. This is my preferred way to get mine filled.
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Old 12-24-2017, 04:09 PM   #25
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Two safe methods to fill cylinders, according to the US "bible" for propane, NFPA 58 (link below):

1. Fill by volume. Open the bleeder valve; fill until it spews; immediatly close the bleeder valve.

2. Fill by weight. Set scale to reflect (a) capacity of cylinder in pounds + (b) tare weight of cylinder + (c) weight of filling apparatus.

Note that under NO circumstances are fillers permitted under these codes to fill based on the behavior of the OPD valve.

Of course, some fillers do both method (1) and method (2) at the same time. Kind of overkill, given that they amount to the same thing. Nonetheless, sometimes a filler will run into a curious situation regarding some cylinder or another; better safe than sorry.

NFPA standards are not national; they are offered by the codes association, and states are free to accept fully, reject, modify, whatever. Some states may, for instance, prefer or even require one filling method over the other. A common reason is that filling by volume, number (1) above, inevitably spews some propane into the air.


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http://www.nfpa.org/codes-and-standa...detail?code=58
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Old 12-24-2017, 04:09 PM   #26
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o, I opened the valve, bled it for about 30 seconds--and the problem seems to be resolved. What do you think?
I think you needn't have bothered; it wasn't really a problem. The pressure relief valve would have bled off enough propane without you having to do anything.

If you fill a propane cylinder when the air is cold, you can get more propane into the cylinder than if you fill it when the air is warm; unlike water, the weight of a gallon of propane changes with temperature. 80% full at 45F is more propane by weight than 80% full at 75F, for instance, even though the volume is the same.

If a cylinder that's filled in the cold is left in the sun and heat, the propane inside will warm up (and yes, it may boil) and expand, allowing pressure to build until the relief valve opens to vent some pressure. Then once the pressure drops to a safe level, the pressure relief valve will close itself, and everything will be copacetic.

Nothing is ever completely idiot-proof. But modern propane cylinders in good working order are about as close to idiot-proof as you will find.
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