Here is a reply I received a few years ago when I was trying to get the "truth" about the infamous "Overfill Protection Device" or "OPD" that became mandatory on all 40# and smaller propane cylinders in about 2002:
Date: Mon 11/18/02 12:49 PM     From: Lemoff, Ted     To: email@example.com     Mr. Stanaitis , You asked:
I have heard that the new tanks with the OPD valve also have an output orifice that limits flow to some limit much lower than that of the old cylinders. I use 20 pound and 40 pound cylinders to fuel a portable gas forge in blacksmithing and to run 2 160,000 btu burners for cooking down maple syrup. If this is true, then I won't be able to use the new tanks for these purposes. What is the truth here?
I have just found your site and in the FAQ there's a comment about an exemption for inudustrial use, etc.. It says that the tanks must be so labeled for that use. Can I simply use indelible markers to mark my tanks for this use?
First Question: Yes there is a limiting orifice in most OPD's sold. This is a requirement for gas grills, and most cylinders are used for gas grills. OPD valves are available without orifices (or with larger orifices) for other uses, such as yours. Contact your propane supplier. If they can not help, ask them where they buy their OPD's and talk to the supplier.
Second Question. There is an exception for cylinders used for industrial
welding and cutting gases. Your application does not appear to fall in this
For more info, see the following:
I believe that this answers your question. Please feel free to contact me if I can provide any additional information on NFPA codes and standards.
This correspondence is not a Formal Interpretation issued pursuant to NFPA Regulations. Any opinion expressed is the personal opinion of the author, and does not necessarily represent the official position of the NFPA or its Technical Committees. In addition, this correspondence is neither intended, nor should be relied upon, to provide professional consultation or services.
Very truly yours,
Theodore C. Lemoff, PE
Principal Gases Engineer
Web Site: www.nfpa.org