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Jul 23, 2009 06:44 PM

Propane Tank Gauge

Anyone have a recommendation for a propane tank gauge? Amazon sells one that looks pretty nice ( but reviews on it are mixed. Thanks.

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  1. A scale. Propane tanks are filled and measured by weight. There's an empty weight stamped on the side of the collar that protects the valve. It'll say TW 17.8, or something close to 18 lbs, for a 20 lb tank, the standard grill size. Empty, it weighs 17.8 lbs (or whatever is stamped there.); full, it weighs 20 lbs more. Of course, if you take your tank to an exchange place, you're only getting 15 lbs these days.

    There's no reliable way to convert from the pressure in the tank to the volume of propane left. Propane is a liquid under pressure, so what you've got in the tank is a liquid, with a high pressure gas layer above that. As you use gas, some of the liquid vaporizes to keep the pressure reasonably constant. The equilibrium pressure varies with temperature, and at low temperatures, and high draw rates, the gas pressure can fall well below that, even with plenty of gas left in the tnak. To get an accurate measure of the gas available, you need a scale (or a finely calibrated arm; I used to fill propane tanks, and could tell with in a pound or so how much was in them just by lifting them) or a float in the tank, which isn't an option on standard propane tanks.

    1 Reply
    1. re: dscheidt

      Interesting. I never thought about how it would work from a physics aspect. I guess that would explain why those gauges aren't very accurate.

      I guess I could always stick to the "pour hot water down the side" method or invest in a scale.

    2. I have a gadget with a magnet to hold it low on the tank. It plays a tune when the gas level reaches the sensor. It works OK as a warning that I'm getting low on gas. But I find the only real solution is to have a second tank available when the first tank runs out of fuel. Most places I buy propane in fact asume that the tank is empty when you take it in for a refill. You can tell because the don't reset the scale.

      3 Replies
      1. re: mexivilla

        There's no reason to reset the scale. The pump turns off (or the operator turns it off) when the scale trips. A 20 lb tank of propane holds (surprise, surprise...) 20 lbs of propane, weighs about 18 lbs empty, and the hose and valve weigh a couple pounds. Set the scale for 40 lbs, and it trips when the combination weighs 40 lbs. Doesn't matter if it starts out weighing 20 lbs (what an empty tank and hose do) or 39 lbs. the tank filler doesn't care how much propane it takes, since they're usually charging a flat rate. (If they're honest, they should tell you you're tank is more than about 1/2 full.)

        1. re: dscheidt

          It really doesn't matter what you're weighing a scale should always be reset to the tare weight to obtain an accurate measurement. And surprise, surprise a 20lb. propane tank can hold more than 20lb of propane. The 20lb is the legal limit set at about 80% of real capacity.
          It's strange that we are so accepting of the method of propane tank refill which we would never accept in a butcher shop.

          1. re: mexivilla

            NO. NO. NO. NO. It's idiotic statements like "a 20lb tank can hold more than 20lbs" that have saddled us with the overfill protection device valves. Propane tanks filled to 80 or 85% of liquid capacity to allow for the change of vapor pressure and the expansion of the liquid propane with increased temperature. It's safety, not a conspiracy to make you fill your tank more often.

      2. I have one and it seems to work well enough. I agree about weighing it for an accurate measurement but I don't have a scale I wanna leave out on the deck.


        1. Our current Gas Grill (which hardly ever gets used, 'cause charcoal is so much better... but I digress) has a built in scale, calibrated to let you know by % how much gas is left.
          And yes it seems that a couple of the local re-fill stations are shorting on the fill-up. When questioned one owner said "didn't think any-one would know".


          1. We had one and it worked for a while, but then it seemed like it was interfering with the gas output to the grill. Plus, we learned through trial and error that you have to push down on the gauge to get a reading (much like tire pressure gauges).

            In the end, we just bought a second small tank. If the first one runs out, we switch it out for the full one and then go exchange the empty one. This way, we also know that the one we're exchanging is completely empty, instead of guessing.