Propane Tank Question

Yes

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.

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.

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

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.

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.

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.

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.

ACME excess flow does not shut completely if operating properly.

two safety features are built into the Acme nut itself. First, Acme nuts contain a thermal bushing, which will melt in a fire, and prevent the escape of gasses from the tank. When it melts, it allows the new OPD spring activated shut off valve, which will only allow the flow of gas if a fitting is attached, to pop out and completely shut the flow down. They also have an improved excess flow check valve,

Now to the new style excess flow check valve on the Acme nut that connects to the DOT cylinder's OPD valve. It is really a simple device. Inside the Acme nut, there is a ball bearing check valve that almost shuts off momentarily when full pressure is released by opening the cylinder valve. You should hear a click at that point. It doesn't shut down completely, as that would negate its ability to detect leaks and excess flow from a leak or major line break, and no gas could flow. It closes just enough to allow a bypass of gas that is very slight, about 10 cubic feet or less per hour (cf/hour) flow, as opposed to the max flow of 200 cf/hour. The bypass gas goes into the propane system, and if there are no leaks or broken pipes, it backs up and builds pressure in the gas lines in the RV. When it equalizes on both sides of the valve, the valve opens to allow full pressure up to about a max of 200 cf/hour at 100 psi. Then if you were standing there, you would hear a second click.

http://home.earthlink.net/~derekgore/rvroadiervfulltimingwhatisitreallylike/id44.html

There is a spring loaded shutoff vlave in the end of OPD service valve that will not allow propane flow unless a hose is attached that pushes the spring loaded shutoff valve open.

There is a ball check valve inside the ACME nut that moves closed when opening a OPD valve until downstream pressure builds up/equalizes and then the ball check valve moves back to center position allowing full flow.
If OPD opened to quickly the ball check valve will stay in closed position.
If a downstream leak should occur the ball check valve moves from center to closed position.



OPD Spring loaded Valve #24 (Pushed Open by #66 in ACME Nut)

ACME Ball Check Valve #86