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#1
Old 03-23-2008, 04:30 PM
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How do I tell when my Blue Rhino propane tank is empty?

I have a gas grill that uses a single fuel tank. Last time I tried to grill, I noticed it was difficult to get the temperature up to an appropriate level, and thought I might be low on fuel. However, when I took the tank out just now to trade it in, it still seems to be quite heavy.

Is there any definite way of telling, besides the grill not getting as hot? It doesn't seem like I've used it that much, since I got this tank.

How long is a tank expected to last if you barbecue, say, twice a week through spring and summer?
#2
Old 03-23-2008, 04:36 PM
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One way is to pour very hot water down the side of the tank -- the propane is quite cool, and will thus chill the water. There are temp-sensitive LCD strips that can help you. Also, weight is a pretty good indicator -- many higher-end grills have a built-in spring scale that will tell you roughly how much fuel is left; you might be able to find a kit that will retrofit to your existing grill.
#3
Old 03-23-2008, 04:42 PM
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Quote:
Originally Posted by 3waygeek
...the propane is quite cool, and will thus chill the water.
Not quite. The propane is the same temperature as the rest of the cylinder and the ambient air, assuming it's just been sitting around and not being used at a high flow rate--which will cause the propane to cool off under the same principle as an air conditioner. However, the liquid propane has a much higher thermal capacity than the gas above it, so when you pour hot water on the tank the metal backed by gas gets hot quickly, but the liquid absorbs the heat readily so the metal there doesn't get as hot.
#4
Old 03-23-2008, 04:46 PM
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Thanks for the correction -- it's been a long time since my last physics class. I'm duly chagrined, as physics was one of my undergrad majors.
#5
Old 03-23-2008, 04:59 PM
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Quote:
Originally Posted by 3waygeek
One way is to pour very hot water down the side of the tank -- the propane is quite cool, and will thus chill the water. There are temp-sensitive LCD strips that can help you. Also, weight is a pretty good indicator -- many higher-end grills have a built-in spring scale that will tell you roughly how much fuel is left; you might be able to find a kit that will retrofit to your existing grill.
You don't even need that. A grill-size tank of propane should weigh about 20 lbs plus the cylinder weight (marked on the tank with TW and generally about 18 pounds) when full or close to full. Empty, of course, it should just be the cylinder weight. Stepping on your bathroom scale with and without the tank in hand should give you a good enough idea. Each gallon of propane left weighs about five pounds. So, for example, if your cylinder's tare weight is 20 pounds and the whole thing weighs 30 pounds, you've got half a tank left.
#6
Old 03-23-2008, 05:27 PM
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Is there a reason you can't just open the valve to find out if you didn't want to buy a pressure gauge for about $30.

Last edited by Will Repair; 03-23-2008 at 05:30 PM.
#7
Old 03-23-2008, 05:37 PM
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The new OPD valve is designed to prevent the flow of gas out of the tank if it isn't connected to a device. This link will give some explanation.
http://propane101.com/opdcylindervalves.htm

How-ever, if the tank onnection isn't tight the flow may also be restricted. You probley won't find this information on a site related to OPD valves.
I have many times hooked up a tank and had problems with flow, I have been able to remedy this by loosening the tank connection and re tighten it and "Open The Tank Valve Very Slowly". The OPD valve also is a flow restricting valve and just doesn't let the flow through like the old valves.
If your tank is mounted in a bracket that holds it tilted, You Could also have problems. The float lever could close the valve just enough to give you problems.
These valves have some great features but over all they are a PITA
http://ths.gardenweb.com/forums/load...613123088.html

Last edited by Gbro; 03-23-2008 at 05:40 PM.
#8
Old 03-23-2008, 05:42 PM
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>the propane is quite cool, and will thus chill the water.
>Not quite.

Not quite not quite. The propane is indeed quite cool, compared to the water, which is the relevant comparison. It will chill the water more effectively than the gas-filled part of the tank will.
#9
Old 03-23-2008, 05:44 PM
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Quote:
Originally Posted by Napier
It will chill the water more effectively than the gas-filled part of the tank will.
Uh, yeah. For the reasons I outlined.
#10
Old 03-23-2008, 06:14 PM
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Quote:
Originally Posted by Gbro
The new OPD valve is designed to prevent the flow of gas out of the tank if it isn't connected to a device.
Thought so but figured the local store would balk at gathering empirical evidence. So an inexpensive inline pressure gauge seems the answer.
#11
Old 03-23-2008, 06:21 PM
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The OPD valve can also be triggered by opening the tank valve when the burner valve(s) are turned on. It reacts to sudden flow by shutting off the flow of gas. Make sure all burner valves are closed, and slowly open the main gas valve first before opening the burner valve.
#12
Old 03-23-2008, 06:46 PM
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I see no reason to make this more complicated than it needs to be.

asterion nailed it. The "Tare Weight" (TW) is the weight of the empty tank.

You want to know how much more you have left? Take a digital bathroom scale and weigh the tank. It's just that easy.

Anything above the tare weight is propane. Take the total weight, subtract the tare weight and divide by 5, and you have the amount of propane. (expressed in pounds)
#13
Old 03-23-2008, 07:01 PM
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Quote:
Originally Posted by Will Repair
Is there a reason you can't just open the valve to find out if you didn't want to buy a pressure gauge for about $30.
Opening the valve tells you if there is some propane left, not if there is enough to last until the meat is cooked.

The pressure gauges are useless. As long as there is any liquid propane (LP) in the bottom of the tank, the pressure is determined by the temperature, not by the remaining fuel. Pressure gauges work fine for products that do not liquefy at room temperature, such as oxygen, nitrogen, helium, argon. Some of these are available as liquid in Dewar bottles, which again make pressure meaningless as to gauging the quantity remaining.

CO2, Propane, Butane, and refrigerants are the most common "gasses" delivered in a non refrigerated liquid state.

Last edited by Kevbo; 03-23-2008 at 07:03 PM.
#14
Old 03-23-2008, 07:52 PM
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Kevbo makes an excellent point. In fact, I have the same problem with CO2 (for my beer). The gage doesn't mean anything until all the liquid is gone, and by then, it's just too late. Luckily I have a spare bottle, and so don't worry about tare weights and scales. My propane grill must be one of the high-end ones, as it has a basic scale that tells me fairly well whether the tank is running close to empty. I'd like a spare tank, but just haven't gotten around to it (I keep telling myself I'm going to change the burner and run natural gas to it).
#15
Old 03-23-2008, 11:30 PM
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Quote:
Originally Posted by Bill Door
The OPD valve can also be triggered by opening the tank valve when the burner valve(s) are turned on. It reacts to sudden flow by shutting off the flow of gas. Make sure all burner valves are closed, and slowly open the main gas valve first before opening the burner valve.
No it doesn't, it is just an ugly float on a hinge that extends from the threads on the valve. That's like saying a toilet valve shuts off if you flush too fast.

I've had valves close when filling them from, presumable, the propane rushing IN too fast and splashing up forcing the float upwards. But closing the valve and then opening it again quickly fixed that. I used to work at an Ace Hardware store filling propane all the damn time.
#16
Old 03-23-2008, 11:40 PM
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There are many problems associated with the OPD valves.
This is some interesting information i found,


Q: Roofers and other commercial customers are trying to use OPD equipped tanks on
torch applications and they are not getting an adequate flow through the valve. What
can we do about this?
A: Some of the early OPD valves had an insufficient flow capacity for certain types
of service such as high-pressure torch applications. Market competition has
resulted in OPD's becoming available that have significantly greater rates of flow.


Although several tank distributors claim there valve has a high(er) flow rate, I find nothing that would indicate how one would tell one from the other
Mighty Flame Blue Rino and Jet Gas make this claim.

On Blue Rino site;
http://ww2.bluerhino.com/br/TankExch...ons/index.html

The OPD valve has a safety feature that sometimes restricts gas flow if the tank is turned all the way on. We recommend that you turn the tank valve one turn (360 degrees), light up, and then use smaller turns for a higher flame. The normal procedure is to turn the tank on and then turn the grill controls on, but doing this with a tank equipped with an excess flow device will sometimes cause the "check valve" to prematurely activate.


In reference to the second possibility, please check to be sure your connector to the tank is over an inch long. This should be enough to push back the check valve inside the valve. If it is too short, then you will need to get another connector.


This is something I am going to check on my grill.

Does the outside temperature have any effect on pressure?

According to NFPA 58, for a tank with 20 pounds of gas, at -

* 70 degrees F - the pressure would be about 145 psi.
* 90 degrees F - approximately 180 psi.
* 105 degrees F - approximately 235 psi.
* 130 degrees F - approximately 315 psi.


It is worth noting that tanks equipped with OPDs hold only about 17 pounds of fuel, which results in lower pressures at the above temperatures.
Now this one has me wondering why we are still paying for 20 lbs of propane.
#17
Old 03-23-2008, 11:42 PM
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It's not the OPD that does it, but many tanks have another valve that activates, and stops the flow if it exceeds some rate. Also, many are set up like a schreader (tire) valve and require that a mating connector depress a pin in order to allow any flow.
#18
Old 03-23-2008, 11:51 PM
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Quote:
Originally Posted by Kevbo
It's not the OPD that does it, but many tanks have another valve that activates, and stops the flow if it exceeds some rate. Also, many are set up like a schreader (tire) valve and require that a mating connector depress a pin in order to allow any flow.
So true, BUT that other valve is ALSO an "INTEGRAL PART of the OPD VALVE"
#19
Old 03-24-2008, 12:22 AM
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All you have to do is pick it up. You won't know much the first time until it runs out but afterwards it should be obvious. I get Blue Rhino tanks and I have never had a problem just lifting it and feeling the weight. They also feel hollow and empty when they are spent. My wife has problems with that concept however and often runs them dry. However, I still think it is very easy just to pick one up with one hand to know if you need to do an exchange.

Last edited by Shagnasty; 03-24-2008 at 12:24 AM.
#20
Old 03-24-2008, 12:56 AM
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Or just get one of these and follow the info that asterion provided.
#21
Old 03-24-2008, 01:00 AM
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Quote:
Originally Posted by Gbro
<snip>

It is worth noting that tanks equipped with OPDs hold only about 17 pounds of fuel, which results in lower pressures at the above temperatures.
Now this one has me wondering why we are still paying for 20 lbs of propane.
I'm not sure if this is something you've quoted or something you're saying, but as noted above, when there is any amount of liquid in the tank, the pressure is only dependent on temperature.
#22
Old 03-24-2008, 06:09 AM
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I just keep two (well actually three) tanks on hand. When one runs down, I swap it for the full one and then exchange it my convienence.
#23
Old 03-24-2008, 11:12 AM
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Quote:
Originally Posted by Santo Rugger
I'm not sure if this is something you've quoted or something you're saying, but as noted above, when there is any amount of liquid in the tank, the pressure is only dependent on temperature.
Everything i put in italic is from a web site, and i posted a link to the site for that .Quote

That site is the most informative i have found on the web.
Additionally, I did some calls to local propane services and here is what i found.

A. Yes there are valves(OPD) that have a very reduced flow rate. some refer to them as early model valves. But don't let that mislead you to think all valves will be ok from now on. My source stated that with the valve in hand, one can tell by the size of the shut off wire from the float if the valve is a higher flow. the cheap one will have a smaller diameter wire. These cheap ones are still found in the marketplace. Also this source told me he can tell by the rate of filling the cylinder. This is something he has the experience in doing.

B. As to the information on the BlueRino site pertaining to 17lbs, This source stated that "yes you can fill a tank to 20lbs" (Makes one wonder)

C. The OPD valve (overflow Protection) is 4 valves in one.

1. overflow float that stops the filling process before the cylinder is filled past the 80% Max. This float is also designed to stop flow in the event the cylinder is tipped. A tipped cylinder w/o the OPD would dispense liquid and is a very dangerous situation.

2. Is a over FLOW check, this is in reality a velocity fuse, and is incorporated in the valve(opd) to stop the gas flow from cylinder in the event of a major leak. an example of this would be a blown hose, or a hose burned off by a fire. This is the feature that gives us problems when we open the tank valve to fast, and is recommended by some to only open the valve 360 deg, or 1 full turn then adjust your ned for more heat by opening the tank valve more. I myself have elected to make it a practice of opening the tank valve very slowly the 1st turn, then open it fully from there.

3. Is the discharge check, This feature prevents gas from being dispensed from the cylinder without having a device hooked to it. This feature can cause low flow problems if the connection isn't fully seated(tightened properly), or it might have the wrong seal ring on it preventing full opening of the discharge check.

4. This of course is the manual on-off hand wheel

So is there any wonder we experence problem with these new valves?

Therefore it is so very important to keep the protective caps on these valves. If your cap is missing don't wait to have it replaced by the tank vendor, just wrap a piece of aluminum foil around valve connection, or bag it.
#24
Old 03-24-2008, 01:49 PM
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This thread reminds me why I need to get off my ass and invent a device that will measure the amount of propane left in a tank and convert it into Burnerhours (tm), i.e. how many hours of grilling left at 1, 2, 3, or 4 burners on high. (So 4 Burnerhours left would mean you could grill for one hour with all four burners or four hours with just one burner). I think I would be a millionaire!

Too bad I'm not an inventor and wouldn't have a clue where to begin
#25
Old 03-24-2008, 02:17 PM
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Quote:
Originally Posted by ShadowFacts
Too bad I'm not an inventor and wouldn't have a clue where to begin
It would be different from grill to grill, but perhaps you could put a tank on a scale. Let one burner run on high for an hour and check the new weight. Do some simple math and there you go, your very own burnerhour meter.
#26
Old 03-24-2008, 02:54 PM
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Quote:
Originally Posted by Joey P
It would be different from grill to grill, but perhaps you could put a tank on a scale. Let one burner run on high for an hour and check the new weight. Do some simple math and there you go, your very own burnerhour meter.
Then don't forget that you forgot to turn it off after you left it on to cook clean.
I could go with a timed turn off
#27
Old 03-25-2008, 03:02 AM
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Quote:
Originally Posted by Gbro
Now this one has me wondering why we are still paying for 20 lbs of propane.
Around here, you pay by the gallon.
#28
Old 03-25-2008, 09:45 AM
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Quote:
Originally Posted by gotpasswords
Around here, you pay by the gallon.
That would be great, but here its like $16.00 for a fill, and it doesn't matter how many gallons. But it is suppose to be based on 20#'s. They say it keeps the anal-retentive from driving then Bonker's .
#29
Old 03-25-2008, 01:19 PM
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Quote:
Originally Posted by Gbro
That would be great, but here its like $16.00 for a fill, and it doesn't matter how many gallons. But it is suppose to be based on 20#'s. They say it keeps the anal-retentive from driving then Bonker's .
Blue Rhino is a cylinder exchange. You swap your empty tank for a full one, pay and drive away. Blue Rhino sites don't have the equipment to fill your tank. Tanks are cleaned and filled offsite. So there is no such thing as a partial tank. Yes, you pay a little more, but in my town of 20k people, there are at least 10 places where I can go at 6pm on Sunday, when my tank runs out, and get an exchange in about 5 minutes. It's all about the convenience.
#30
Old 03-26-2008, 02:40 AM
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I will respectfully retract some of the comments,

I have disassembled a OPD valve assembly, and some of the information i received from a propane service center doesn't check out.
I will do some Lab work on flows and fittings, as the fittings connecting to the OPD valve are a big factor in the malfunctions i was posting about.
Respectfully,
Gbro
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