Trailer or camper LP tank in the last few years, you've no doubt learned you need the (not so) new tank valve, an OPD valve, or "overfill protection device." The theory here is that a little device on the valve will prevent the container from being filled more than 80% full, allowing for vapor expansion in the tank. We say theory, because many LP dealers tell us that it doesn't always work that way. Hence, whenever your LP dealer refills your bottle he should open a small "20% valve" which will spit forth liquid LP when the tank has reached its safe filling point. A safe fill means STOP filling at that point. Overfilled LP tanks are risky.
DOT tanks (the kind found on trailers and campers) are initially certified for 12 years from date of manufacture. After those years, they should be inspected and recertified, usually for 5-year intervals. Most LP dealers can do the inspection and "recert," and it doesn't cost a lot of money--some even do it for free. In many localities, if your tank is "out of date," a legitimate dealer won't refill you.
Pay attention to tank position when transporting it or having it filled. If your tank sits vertically in use, it should be transported and filled in that position. If it's a horizontal tank, common in truck campers, then transport and fill only horizontally. That can be a problem with rookie LP filling station attendants--they think all tanks should be filled vertically, and you may need to educate them--in strong terms. OPD tanks don't need to have a plug screwed into the valve mouth while transporting, but putting the dust cap on isn't a bad idea.
When you get your tank home and go to hook it back into the LP system you'll find either a "POL" style fitting on the end of your rig's "pigtail," or one of the new "Acme" fittings. POL fittings are common on older rigs and require a 7/8" wrench to put in. This is a LEFT hand thread fitting that screws into the tank valve, while the Acme fitting is a right hand thread that screws on OVER the tank valve, and is done by hand. The new OPD valves will accept either fitting. When tightening a POL fitting, take care not to over tighten, use your wrench yes, but don't go beyond "just snug." There's an internal rubber seal in the mouth of the valve which over tightening will tear up and eventually cause a leak. In some valves these can be replaced, but in others, a leak will require a whole new OPD valve.
And a note on those Acme fittings: Reports from some RV dealers indicate that the Acme fittings may wear out quicker than the old POL fittings. It may be RVers are just over-torquing them, so go gentle. We know one dealer won't sell the Acme pigtails, but instead offers the old-style POL fitting equipped with a "hand wheel" that allows you to hook up without a wrench. He swears it's a great improvement over Acme.
Photo: "Three sided" OPD valve is a giveaway that your tank meets new valve directive.
