horizontal propane tank fill level question

I did a search and find loads of info about horizontal tanks (many of which answer other questions I had) but I haven't found this one particular bit of info. When we take our tanks in to be filled, the gauge never reads more than about 3/4 full. As far as I know, these are the original tanks that came on our used 2002 2720SD. I'm wondering if this is just a quirk associated with filling horizontal tanks OR if the gauge is probably not accurate OR the propane filler is just not doing it right?

Not really a big deal-with 2 tanks I can easily change as needed, but this particular fill station gives a free fill after 5 tanks are filled (and in addition their price is usually lower than other in my area). But the last couple times they've told me they wouldn't 'punch my card' because my tank wasn't empty when I came in (or else it would have held more)

[ZekenSpider]

My experience with horizontal tanks is similar to yours. The gauges never seem to be accurate. They are only to be filled when vertical and are to be filled until liquid comes out of the vent screw. That is really the only way to know they are full.

Propane weighs 4.24 pounds per gallon (at normal temperatures). A full tank should contain 4.75 gallons and weigh 20.14 lbs PLUS the Tare Weight stamped on the tank. This allows for vapor room above the liquid for thermal expansion.

The best way to tell what is left in the tank before you take it to the "filler" is to carefully weigh it, then subtract the Tare Weight stamped on the tank. The difference is the weight of propane left in your tank.

For instance, if the difference is 3.50 pounds, then you have 3.5/4.24 = 0.825 gallons in your tank. Since the "filler" usually uses a Gallon Gauge (he charges by the gallon) he will only be able to legally fill it with 4.75 - 0.825 =3.93 gallons.


Good information can be found at: <http://www.propane101.com/aboutpropane.htm>

Jerry

Thanks Jerry-I had a hunch this was the case. I'm not gonna bother weighing the tanks and just trust that when they won't produce enuf gas to even light the stove that they're empty enough

BTW-I did find, on this board, that some horizontal tanks will have a sticker (or some such thing) saying what amounts to 'use horizontally fill horizontally' -- others might say 'use horizontally fill vertically' (but even those that say 'fill horizontally' will experience no problems if filled vertically). I haven't noticed if my tanks have any notice at all, but I'll look next time

I don't think my tanks on my 2720SL had a sticker-----But shopping at a RV Supply store I saw 2 tanks (standing upright) that has a sticker saying use horazonicly fill vertical.

[hillbillyhotel]

just my 2 cents,
i may be wrong but i think that tanks can only be filled to 80% max. even when thay fill my home tank it will only shows 80% after filling .
it has something to do with the tank haveing room for propane to become gas ,

If you fill propane tanks ( any propane tanks) to 100% they will not work. Filling adds liquid propane to the tank while appliances burn propane gas. There needs to be sufficient " head space" for the liquid to transform into a gas at a sufficient rate. The mechanics of the gauge for the horizontal tank are such that the gauge shows about 80% when full.

The 80 percent fill level for smaller propane tanks is a safety issue. Liquid propane expands and contracts more than liquid water with changes in temperature. Maintaining a vapor space gives the liquid somewhere to go as it expands. An overfilled cylinder exposed to excessive heat could rupture due to the high pressures caused by the liquid pressing on the cylinder walls, welds and so forth. People have been killed by defeating the overflow protection devices, probably thinking they were being ripped off by suppliers only filling to 80 percent. This is one reason new cylinders now come with an overfill protection valve (OPV). It is impossible to liquid fill these cylinders, the valve shuts off and prevents additional liquid entering the cylinder.

Larger storage tanks may use 85 percent as the full level, but they will all have vapor above the liquid. Propane does not need a vapor space to deliver gas, with a boiling point of -43.6F (-42C) it will vaporize readily even in the coldest weather.

Yes, I fully realize that it takes vapor space so the tanks are never filled completely...but I guess my past tanks that had gauges took that into account in the calibration of the gauge. I guess I wrongly assumed that would also be the case with TM tank gauges as well

[ShrimpBurrito]

Originally Posted by CeeWoo

When we take our tanks in to be filled, the gauge never reads more than about 3/4 full.

This happens to me too. I always attributed it to the OPD, but regardless, there is propane gas coming out the vent that the filler unscrews when the tank is full. But that may happen because the OPD closes the tank valve, preventing more gas from being pumped in.

Dave

[Lesherp]

I took a look at my gauges the other day before taking one that was reading 1/4 full to be filled before we left for Utah. I had been observing the reading above the needle that when upright now read about 1/2 full. As I was looking at it I noticed there was a green (ok) and red (add) gauge below the needle with the word vertical above it. When I tipped the tank on its side the reading on the red and green gauge appeared to be about half way to add. When I had the tank filled it was about half empty and the upper gauge read 3/4 and the lower was off the charts when mounted. I am going to keep a eye on it this trip and see if it may be the lower gauge is the one to use when you have your tanks mounted horizontally.