Propane tank gage (in)accuracy question

[bikemutt]

The good news is we survived our first camping trip, Lincoln City Oregon KOA, the folks there treated us right .

My question concerns the gage on each propane tank. When I filled both tanks, the gages indicated yellow just a nick away from red, close to empty. In both cases the tanks accepted only 3 gallons each. Since these are 5 gallon tanks, I'm trying hard to reconcile the gage indications versus reality.

Looking for some guidance on propane tank gages, thank you.

 

[Ray-IN]

By federal law any LP tank/cylinder can only be filled 80% capacity to allow room for expansion and for the liquid to return to gaseous form.

 

[LMHS]

If your tanks are new, they should have been purged of the air first (I ALWAYS tell the fill station attendant that I have a brand new tank so they know to purge the air before filling it). My 20LB (BBQ) tanks holds about 4 to 4-1/2 gallons when filled (depends on how empty the tank is and the ambient temperature). Older tanks can accumulate condensation inside the tank over the years as well, although it sounds like your gauge is off or you have a tank that was not purged. I mostly use the tank gauges as a "leak detector". I really don't trust them to be real accurate, especially with cold nights and warm/hot days. I try to read them during the warmest part of the day.

 

[CharlesinGA]

Need to know more about the tanks. The most common ones are 20 lb Flame King cylinders with a gauge. Is this what you have? Only other I know of is a Manchester tank with a gauge on it, very expensive however.

It does sound like the tank was no properly purged, or not vented during filling.

Charles

 

[John From Detroit]

There are basically two types of gauges. The video above shows one and once you learn where "Full" and "empty" are.. they are very consistent They may NOT be linier (That is they may move faster at different parts of the dial) but they are consistent. (That is if they say for example 1/4 full well you will always have the same liquid level every time they say that. )

The other type of gauge is normall found at the regulator or selector valve and it;'s a "you got gas/you don't got gas" they are just Red/Green. no yellow

There is a third type. but it's not part of the tank or the plumbing. it's a scale. and very accurate.

 

[NY_Dutch]

There's fourth gauge type that's both linear and quite accurate. It's an ultrasonic sensor that attaches to the bottom of the cylinder by magnets, and is read using bluetooth to an app on your phone or a separate display. There's a few hand held ultrasonic sensors as well, but I'm not familiar with them.

Sonar Powered Tank Monitoring | MopekaIOT

Find out how MopekaIOT's patented sonar powered tank monitoring system can benefit you or your business.

mopeka.com

https://www.amazon.com/s?k=mopeka+propane+tank+sensors&crid=379DVAXN2ZPCO

 

[bikemutt]

Need to know more about the tanks. The most common ones are 20 lb Flame King cylinders with a gauge. Is this what you have? Only other I know of is a Manchester tank with a gauge on it, very expensive however.

It does sound like the tank was no properly purged, or not vented during filling.

Charles

Both our tanks are the Flame Kings, brand new.

 

[Wasillaguy]

There's fourth gauge type that's both linear and quite accurate. It's an ultrasonic sensor that attaches to the bottom of the cylinder by magnets, and is read using bluetooth to an app on your phone or a separate display. There's a few hand held ultrasonic sensors as well, but I'm not familiar with them.

Sonar Powered Tank Monitoring | MopekaIOT

Find out how MopekaIOT's patented sonar powered tank monitoring system can benefit you or your business.

mopeka.com

https://www.amazon.com/s?k=mopeka+propane+tank+sensors&crid=379DVAXN2ZPCO

I have this device and can attest it's very accurate. Only complaint is it has no on/off switch and will drain it's battery every season if you don't pry open the case with your pocket knife and remove the battery after every use.

 

[Gary RV_Wizard]

The Flame King valve uses a float so it measures right, but the moving magnet gadget that drives the wireless gauge introduces a degree of measurement slop (error). Maybe a lot, based on your observation. For the best accuracy, be sure the detachable gauge is firmly in position.

Even with only 3 gallons added, the tank should be at least 2/3 full (3/4.5) and the gauge should show approximately that, i.e. somewhere between 55%-75% and easily into the green part of the scale. If neither of the gauges are in that range, you are entitled to make a complaint to Flame King. However, given that propane filling attendant skill varies widely, I think I'd have a different place top off the tank to make sure they are really full. Or weigh the tank yourself to get an actual measure of the contents. Stamped on the collar of the tank will be the Tare Weight (TW), which is the weight of the metal tank alone. Weight the tank with the gas then subtract the TW. Divide the remainder by 4.2 to get the gallons of propane, or simple divide the gas weight by 20 to get the percentage full.

 

[NY_Dutch]

I have this device and can attest it's very accurate. Only complaint is it has no on/off switch and will drain it's battery every season if you don't pry open the case with your pocket knife and remove the battery after every use.

I'm using four Mopeka standard sensors and two Pro sensors. The batteries usually last at least six months, sometimes up to nine months.

 

[CharlesinGA]

I have two Mopeka Pro sensors (after both of the standard sensors got moisture in them and failed, they gave me Pro sensors) They have been installed a couple of years now and are still running on the original batteries. They are quite accurate.

Charles

 

[jymbee]

If your tanks are new, they should have been purged of the air first (I ALWAYS tell the fill station attendant that I have a brand new tank so they know to purge the air before filling it).

NOW you tell me!

But seriously, I never realized that as I almost always have purchased propane tanks that were pre filled.

However, prior to the last trip we bought a 5 pounder for the more convenient size. We have our RV propane tanks filled at a nearby Tractor Supply before we head out and since the 5# was new, asked him to fill it.

He had quite a time after multiple attempts and finally told us there seems to be something wrong as it would not take propane. The weird thing is that the tank felt a bit heavier and we ended up using it quite a bit.

Whether the fact that it was new and he didn't realize that or perhaps that had nothing to do with anything and there was something else going on, I don't know. Bottom line is thanks to your post I now know where to at least start if/when filling a new tank.

 

[markandkim]

Mopeka's work awesome.

 

[bikemutt]

I have the Mopeka unit saved on Amazon.

What I may try first is to bring along our postage scale and weigh a tank as it goes from full to empty, I'll take pictures of the gage at each weight, then see if I can make a useful marked-up composite picture with more intuitive (to me) units, like 50%, 20%, 5% etc remaining. I have a feeling it may be an exercise in futility since the gage appears to be non-linear but, retired cheapskates gotta know .

 

[Ray-IN]

If your tanks are new, they should have been purged as well, although it sounds like your gauge is off or you have a tank that was not purged. I mostly use the tank gauges as a "leak detector". I really don't trust them to be real accurate, especially with cold nights and warm/hot days. I try to read them during the warmest part of the day.

That is not entirely accurate information. water cannot condense inside because the LP contains no water.
About purging:New Propane tank purging is important. LP is heavier than air, when a cylinder is being filled the vapor valve is opened(80% valve) this will push out any air that might be in the cylinder

 

[Gary RV_Wizard]

Purging is important to the function of any propane appliances connected to the tank, but should not affect the gauge operation. If there is 3 gallons on propane in a 4.5 gallon tank, a float gauge should read 2/3 full whether the other 1/3 is gas or air.

 

[dave54]

We used the Mopeka sensors for a few years, and finally gave up. They disconnected from the phone and base unit if you did not use them every few days. Reconnecting is a PITA. It was not defective sensors, we replaced them twice and reloaded the app multiple times.