Since april 2002 propane tanks without opd valves cannot be refilled.
New vs old propane tank valve.
The opd valve incorporates a safety feature that prevents overfilling the cylinder.
Older propane cylinders won t have one but that needn t mean replacing the entire tank at high cost.
This prevents more propane from being added to the tank.
The real difference is that the new tank valves have both a tipover protector and an overfill protector.
Pol valves are the oldest standard for propane tank connections and newer types are more widely used.
Replacing a tank valve with an opd valve can be done at home.
Any new cylinder should come with an opd valve installed.
It is true that the new valves have both male and female threads.
With out the overfill protection they will not or should not fill it.
Tanks with the older acme valves are legal to use and transport but only those with opd valves can be legally filled.
When the level of liquid propane reaches the limit the float rises and the valve closes.
Pol valves allow the release of gas without anything connected to it.
It is not true that you can have an old style tank refilled.
This is an important safety measure.
For the consumer there is little difference between an acme valve and an opd valve.
It is possible to convert a tank to the new valve but you will need to have the tank re certified before it can be refilled.
The next refinement of propane tank connections comes in the acme valve.