Propane filling question

naturist wrote:
Brand new tanks need filled that way to insure that they are purged of air. But there is no reason that I know of to fill used tanks that way. It does waste some propane. I do not have permanently mounted tanks, but around the farm I have a flock of 20, 30, and 40 pound tanks I use for various purposes, and the only times I've had a propane seller use that method at the store I get 99% of my propane from, it was on a new tank. I, too, always take in a number of tanks at once, since there is a price break if you buy more than 18 gallons at a pop.

The reason that the vent is opened is to determine when the tank has reached its 80% capacity.
It should always be opened when filling a tank by volume or weight. Why? Because if the Overfill Protection Device in the valve would fail, that vent is then the only way one would know the tank has reached its fill capacity.

Also, this is the only way one can tell that a fixed tank on a motorhome c
Is filled since it can't be weighed.

Cylinders Filled By Bleeder Valve
Cylinders filled by fixed liquid level gauge, such as forklift cylinders are not required to be filled by weight. They are subject to visual inspections and recertification requirements like all cylinders but are not filled using a scale. Some companies may use a scale but the standard practice is to use the fixed liquid level gauge (bleeder valve). Once the hose end nozzle is hooked up to the cylinder and the pump is turned on, the bottle filler will wait for liquid to spew out and turn off the pump. The bleeder valve will be closed and the hose will be disconnected. The bleeder valve is the indicator letting the attendant know when the cylinder is full. He's not inadvertently letting propane out of your cylinder but rather following the rules and abiding by the law governing cylinder filling.