Before our last adventure at Thanksgiving, I went to fill up the shiny and new (looking) 40 pound propane tanks that came with our 1972 Airstream. When I got to the place to fill them up, they told me they couldn’t do it, because the tanks hadn’t been certified… since 1982!!!

Turns out, propane tanks need to be certified every so often in order to keep using them. The specific schedules vary from state to state, but here in Colorado tanks must be re-certified 10 years after the date of manufacture, and every 5 years thereafter (most states have similar terms).

Luckily, it’s really not a big deal. I went to the local propane place (Metro Gas). They did a visual inspection of the tanks, as well as making sure the valves didn’t leak when closed (turns out they actually did leak when open and hooked up… more on that in another post). It was $9.50 per tank for certification. They engraved their vendor number and the date of inspection on the tank, and I was good to go.

It is against the law for places that sell propane to fill tanks that haven’t been certified. That said, last Thanksgiving when I was on my way out of town and went to fill up at a place that shall go unnamed, what actually happened when the guy told me he couldn’t fill the tanks because they hadn’t been certified was this: I pleaded my case (I was leaving that minute to drive 2000 miles across the US in the freezing cold to visit family), and he went ahead and filled the tanks for us. Actually, the first guy wouldn’t do it, no matter what, but he called someone else out to the tanks, and that person said as long I didn’t tell anyone, he’d do it for me. The first guy wouldn’t even stand there while the second guy filled the tanks though. He said he didn’t want to be anywhere near when it happened so he couldn’t be held accountable.

Another interesting note regarding the purchase of propane: When refilling my 40# RV tanks last week, I took along the 20# tank that goes under the grill. I noted the price to fill it up ($18.91) was slightly less than the exchange rate at Lowe’s, Home Depot, Grocery Store, etc. ($19.99). When I mentioned this, the attendant pointed out that I was also getting almost five pounds more propane at that price! “Look at what’s written on the tank,” he said. Sure enough, the 20# exchange containers state their content weight as only 15 pounds! It turns out that around 2001 when the price of propane rose, rather than adjust pricing significantly for exchange tanks, the companies in charge simply started filling those tanks with 5 pounds less propane to make the cost of a tank exchange remain approximately the same. All this time I thought refilling a 20# BBQ tank was about the same price as exchanging one, but it turns out you are getting ripped off! Not only are you paying more for the propane, but your tank will also not last as long (because there’s less propane in it).

A 20 gallon tank at 70 degrees Fahrenheit is at about 145 psi. At 90 degrees that same tank is at 180 psi. At 105 degrees, it’s all the way up to 235 psi.

A gallon of propane at 70 degrees and 145 psi weighs 4.2 pounds, thus a 20# propane tank (the kind that you use with your grill) should contain around 4.7 gallons (20 pounds) when full.

Since the propane in a tank is under high pressure, it needs to be converted to a lower pressure using a regulator (the silver flying saucer looking thing on the the gas hose that you are likely familiar with if you have a propane grill). Propane for use in an RV for things like the refrigerator, stove, and heater should be at a pressure of 11 water column inches. These days, most RV’s utilize a two stage regulator. The first stage take the tank pressure down to 10-15 psi, and the second stage takes it to a usable and (hopefully) constant 11 water column inches for RV appliances.

 

Standard sizes for RV Propane tanks are 20#, 30#, and 40#.  Usually tanks are vertical, but there are also horizontal tanks.  Horizontal tanks are commonly used for fuel tanks on forklifts, but I am currently researching possibly using them for an Airstream.  It seems like storing tanks on their side is more stable, and I’m also wondering about tucking them up underneath the belly so they are more hidden away (I’ve had locked propane tanks stolen off my rig).