<font color="blue"> purge before filling the first time.</font>
As Bird has mentioned, this was always supposed to have been done, but it was a lot more hit-or-miss before the OPD tanks came out. Essentially, it involves getting the air out of the tank so there will be 100% propane (or as close as possible) inside. The air is what is trapped inside when the tank is closed up at the manufacturer, plus what is used to pressure test the tank before it's shipped. Moisture can also be a problem, but the manufacturers have gotten pretty good about dehumidifying the air in the factory, and many use nitrogen instead of compressed air to do the pressure test. So, moisture is much less of a problem than it used to be, unless the tank has suffered some temperature extremes before filling and condensation results. Even then the amount is tiny.
In the old days, all we had to do to purge was put some propane vapor in the tank, then set the tank aside, open the valves, and let the propane vapor blow out the air. This works because propane vapor is heavier than air, settles to the bottom of the tank, and pushes the air out. Once the pressure has equalized (propane inside, atmospheric pressure outside), no more air can ever get back into the tank unless it's forced in under pressure.
There were some crazy theories. One of my competitors swore that the best way to purge was to put in the propane vapor, then turn the tank upside down and open the valve. Of course, because the propane was heavier, all he accomplished was to let the propane back out, retaining the air in the tank. I tried to clue him in, but he was stubborn, so I just used the facts to convince my customers that I knew a heck of a lot more about what I was doing than did my competitor. /forums/images/graemlins/laugh.gif
With the advent of the OPD tanks and their check valves and tiny orifices, purging became a lot more difficult. The recommended method was to put in some vapor, let it out, and repeat 4 or 5 times. Because it takes forever for the vapor to exhaust through the orifice, purging properly could take up to 20 minutes. For the first time, we started to charge for the purge, simply because of the time it took.
Then, my local state LP gas inspector (who was a good friend, mostly because he knew he would never have any problems with my operation), who was an innovator, suggested that I set up a vacuum purge. Now, they sell vacuum purging rigs that cost hundreds of dollars. But, we had a good air compressor on site. I plumbed the air out to the fill station, then rigged up an air-powered vacuum pump I got from Harbor Freight for less than $20. It works on the venturi theory, in that rushing air past a venturi sucks air from whatever it's hooked to. Also in the rig were some shutoff valves and a regulated feed from a normal 20# grill tank to apply vapor.
The process was to hook up a connector to the tank, close all the valves except the vacuum, turn on the vacuum pump and suck out all the air. The pump would pull down to 28.3" of mercury. good enough according to all the tank mfr. specs, in about 2 minutes. Then we closed the vacuum valve, holding the vacuum inside the tank, and opened the propane vapor valve. Nature abhors a vacuum, so the pro pane, pressurized anyway at around 15 psi, did a lickety-split job of rushing into the tank and displacing the vacuum. Job done quickly and very thoroughly, and we still got to charge a fee for the purge, with the excuse that our sophisticated equipment had to be paid for. Truth is, the most sophisticated part of the who rig was a dual vacuum/pressure guage we picked up for about $24 that normally belonged on the low pressure side of an auto A/C recharging unit. We had no guilty feelings about the fee, because we knew the customer was getting a better purge, and was paying us for our expertise (we charged $3 for the purge).
<font color="blue"> also i have heard that some of the old regulators don;t work right with the new tanks</font>
The regulators are the same. Where the problem comes in is the connection. The old grills and regulators will still work with a new style tank, but the new grills will not work with an old style tank. The reason is because all propane tanks, old and new, have internal threads with a left-hand (backwards) thread. This is because ASME long ago declared that non-flammable gases like oxygen and nitrogen would have right-hand threads, and flammable gases like propane and acetylene would have left hand threads. I think they did this to prevent you from hooking up propane to Grandma's oxygen tent.
The old grills, and all other propane appliances, use what's known as a POL connector. Some say the POL stands for the original mfr, Prest-O-Lite; others insist it means Put On Left-handed. The problem that happened with grills is that they have to be frequently hooked up and unhooked by the great unwashed and untrained masses, most of whom don't even know a left-hand thread exists, and the vast majority of whom don't have a properly sized wrench. The result was lots of leaks from improperly attached tanks, and lots of damage from the leaks.
The first answer was to introduce quick disconnect fittings to the tanks and regulators. Weber and Ducane, and a few very-high end grills, adopted this. The rest of the industry (primarily Charbroil; they own most of the low cost brand names) didn't go along with this because the quick disconnect system was comparatively very expensive (it had to be a lot better quality than the Q/D systems used on air compressors).
The Italians actually figured out a good work-around. It was adopted here and is called the Type I QCC (Quick Connect Coupler). While it was required that the tanks still have the internal left-handed threads, no one said you couldn't add some external threads to the tank nozzle. Since they are in addition to the standard threads, they can be righty-tighty. And, by using a coarse acme-type thread, the connector nut can be large enough to be turned by hand, no longer requiring a wrench. By using an internal O-ring, the connector nut didn't even have to be particularly tight to seal.
This system was just marginally more expensive than the old POL connectors, and was a heck of a lot safer. It became adopted in 1995. There is an additional, very neat safety factor. A check valve was incorporated into the tank nozzle, which has to be forced open by connecting an appliance for the gas to flow. If the connector is the more modern plastic hand nut described above, it has a thermal-sensitive ring that holds it together. If there is a fire under the grill, that ring will melt, the connector assembly will come apart, the center portion will pop out thus allowing the check valve to close, and the gas in the tank will no longer feed the fire. This is very cool!
Interestingly, the OPD tanks actually has little to do with the QCC, which was adopted several years earlier. OPD stands for Overfill Prevention Device, and is the float inside the tank that works like a toilet float. When the liquid propane reaches 80% of the tank's capacity, the float rises and shuts off the flow, thus preventing overfilling. Overfilling is dangerous because if there is not sufficient room for the vapor to expand with temperature increases, the vapor will be exhausted from the pressure relief valve on the back of the tank valve assembly. Of course, the vapor that is released is flammable, and if there's a source if ignition near by, you'll have a Floomph. With a full tank (filled to normal 80%) and enough temperature increase (inside a very hot car trunk or closed garage), even a tank that has not been overfilled will exhaust excess vapor, which is why they say not to store a tank inside, or keep it in a hot trunk more than, say, 2 hours.
Sorry for writing another book, but heck, I'm just sitting here waiting for a hurricane. What else do I have to do? /forums/images/graemlins/confused.gif
