Propane Tank Question

You are terribly wrong, Chris Bryant.
The "pigtail", when screwed into the OPD POL fitting, releases the check valve and allows normal flow of propane, but if you open it too quickly it will freeze the tiny orfice. You can open it very slowly and bring it to full flow, but again, as with a line failure, if it is a sudden burst of propane flow, it will freeze up.
The "pigtail", or longer line, if you wish, has nothing to do with the safety features built into the OPD valves.
I happen to own a propane dispensing station, and about the only time we screw a pigtail in the POL valve is to purge a new cylinder, and many times have opened the OPD valve too quickly and had the flow shut off immediately.

parkmanaa wrote:
Any legal cylinder today, which requires a OPD (overfill prevention device)valve, will shut off if there is a sudden increase in the flow, such as a broken line. The propane passes thru a very small orfice that will immediately freeze closed if the normal flow amount is suddenly exceeded.
This feature is just part of the OPD valve safety features.

That's a bit misleading, the excess flow part is in the pigtail, not the valve. I have a full flow pigtail, and have no problem venting a cylinder at full blast through the OPD valve.

Any legal cylinder today, which requires a OPD (overfill prevention device)valve, will shut off if there is a sudden increase in the flow, such as a broken line. The propane passes thru a very small orfice that will immediately freeze closed if the normal flow amount is suddenly exceeded.
This feature is just part of the OPD valve safety features.

What Doug said- portable DOT cylinders do not have that built in to the tank, it is in the pigtail. The tank has a shutoff if nothing is attached, and shutoff while filling at 80% (the OPD part), but the excess flow valve is outside the cylinder.

True for ASME(motorhome tanks for over 30 years) and DOT Portable cylinders. BUT, on DOT portables it is built into the Pigtails connected to the tank valve in conjunction with the tank valve. On older DOT portables where you have to use a wrench (7/8) to install the POL end and tighten the pigtail, with NO large quick connect threads---NO. Doug

This is a good link to understand LP.

http://www.propanecouncil.org/uploadedFiles/Council/Site_Sections/Marketer_Resources/Safety_and_Training/Workforce_Safety_and_Training/Dispensing_Propane_Safely/Dispensing%20Propane%20Safely%20Training%20Manual.pdf

Maybe not on older tanks. But yes on newer tanks. Often times if your tank is shut of and you turn it on too fast that safety feature will block the valve.
That happened to me just a couple days ago. I couldn't get it to re open by turning the tank back off. So with the tank off I thumped the bottom of the tank with a 2x4. That worked.

Yes it is true for installed tanks. Has been true for at least 20 years but do not know how long it has been requirement.

Yes