Originally Posted by Big Bill
If the tank was exchanged at a hardware grocery etc , the fill is only 15#, they tell you that on the front of the cage , it is a safety thing , check it out
As wmtire eloquently explained... it is NOT a safety thing.
I believe that was verbiage carried over from the older tank days before OPD's and these companies continue to use those words to trick people into believing a tank can only be filled to 3/4 capacity or all hell is going to break loose.
Back in the day, I used to help fill propane tanks and the correct procedure for a proper fill was you either weighed the tank before filling and then add propane to get the proper weight (math involved) or upon weighing (before filling) if you found the tank was completely empty, some filling stations had the ability to dispense the exact correct amount of liquid. You could set the pump for that amount and then it would shut off upon reaching that amount.
The problem with all that was... during filling, there was a bleed screw on the side of the tank valve that had to be opened during filling to allow gas to escape so the liquid propane could fill into the tank. And, it was the fill operators responsibility to stop the fill flow when the tank weighed the correct amount.
If the correct amount was dispensed, nothing but gas would come out the bleed screw and there was room left in the tank for expansion of the liquid propane.
Unfortunately, many filling operators found it easier to forego the weighing (too much math involved) and simply filled the tanks until liquid propane came out the bleed screw. At that point, the tank was overfilled and there was no room for expansion, leaving the opportunity for bad things to happen. (especially if the tank sat out in the sun)
Today's tanks with the OPD valve eliminate all the chance of overfilling (that which I described above) so there is ABSOLUTELY NO NEED to short fill unless the filling/exchange station is trying to make a quick buck.