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Old 03-17-2013, 11:02 AM   #1
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Capacity Indicator - Propane Gas

New Buyer. Does anyone know if the capacity indicator (monitor panel) for the propane gas is full at 80% or full at 100% (therefore if 100% capacity is full, need to fill to 2/3rds on monitor) . The operating manual emphasizes not to exceed 80% and just want to make sure how to manage this when filling up Propane.
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Old 03-17-2013, 11:09 AM   #2
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New Buyer. Does anyone know if the capacity indicator (monitor panel) for the propane gas is full at 80% or full at 100% (therefore if 100% capacity is full, need to fill to 2/3rds on monitor) . The operating manual emphasizes not to exceed 80% and just want to make sure how to manage this when filling up Propane.
Current type "OPD" valves, prevent over filling.

The "OPD" means overfill protection device.

So,in your case, not to worry about overfilling.

Andy
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Old 03-17-2013, 11:16 AM   #3
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Can't tell you about your indicator for sure, but for all other uses I know of, full means full to capacity (80%).

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Old 03-17-2013, 11:42 AM   #4
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The tank level indicator for the LPG tank in your Interstate will almost never show 100% full. When topped up to capacity, it will show 2/3 full. At least, that's how it works with my Interstate.

Unlike water, liquid propane doesn't have a constant weight-to-volume ratio. If you filled the tank to 80% capacity on a very cold day, and then never used any propane until a very hot day, the tank level indicator MIGHT show 100% full then. That's why the OPD won't let tanks be filled above 80% of capacity; the liquid expands as it gets hotter.

Since the tank sensors are just stick-on devices that go on the outside of the tank, they certainly COULD have set them up so that 80% capacity shows "Full" on the display. But they didn't.
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Old 03-17-2013, 12:33 PM   #5
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I take it the Interstates don't have a float type tank unit like the trailers???? Mine shows full on the wall unit (as well as the tank needle gauge) when filled to capacity (80% of total tank volume, per OPD methodology) and is pretty darned accurate all the way to empty.
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Old 03-17-2013, 12:52 PM   #6
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I take it the Interstates don't have a float type tank unit like the trailers???? Mine shows full on the wall unit (as well as the tank needle gauge) when filled to capacity (80% of total tank volume, per OPD methodology) and is pretty darned accurate all the way to empty.
Different type of tanks, ASME spec built-in tank rather than DOT spec portable tanks. The tank sensor panel is TouchSensor Technologies, and the tank sending units are transducers stuck on the wall of the tank. Same type of sensors for Fresh, Gray, Black, and LPG tanks, and all displayed on the same panel. The panel display only shows Full, 2/3, 1/3, and Empty, meaning there are four transducers per tank, at those points. No way to interpolate between the marks, either, so if the 1/3 light is lit on the panel but the 2/3 light isn't lit, it could have anywhere from 1/3 to almost but not quite 2/3 left.
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Old 03-18-2013, 12:35 AM   #7
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While the tank is rated at 18.9 gal, I could only get about 15 gal in and the filling station indicated it was full. But the panel display did show full. Later checked w/ dealer and he confirmed that was the capacity of the tank.
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Old 03-18-2013, 02:19 AM   #8
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Different type of tanks, ASME spec built-in tank rather than DOT spec portable tanks. The tank sensor panel is TouchSensor Technologies, and the tank sending units are transducers stuck on the wall of the tank. Same type of sensors for Fresh, Gray, Black, and LPG tanks, and all displayed on the same panel. The panel display only shows Full, 2/3, 1/3, and Empty, meaning there are four transducers per tank, at those points. No way to interpolate between the marks, either, so if the 1/3 light is lit on the panel but the 2/3 light isn't lit, it could have anywhere from 1/3 to almost but not quite 2/3 left.
Are you sure the tank sending unit is a transducer? Most ASME tanks use a float and the gauge is operated by magnet through a fitting on the side of the tank. There is a 90 ohm variable resister in the gauge that feeds your remote panel. My tank is in the shop right now getting a new valve and gauge. Your's may be different but I have done quite a bit of looking this is to only set up I have seen on the RV tanks. http://www.rochestergauges.com/Pages/PDFs/6200.pdf The nice thing is the gauge can be changed without draining the tank. The accuracy is probably similar to the gas gauge in most cars, close but not perfect.
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Old 03-18-2013, 04:15 AM   #9
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While the tank is rated at 18.9 gal, I could only get about 15 gal in and the filling station indicated it was full. But the panel display did show full. Later checked w/ dealer and he confirmed that was the capacity of the tank.
Mine has NEVER shown full, even when filled to the point that propane was coming out of the OPD valve.
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Old 03-18-2013, 08:25 AM   #10
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Are you sure the tank sending unit is a transducer? Most ASME tanks use a float and the gauge is operated by magnet through a fitting on the side of the tank. There is a 90 ohm variable resister in the gauge that feeds your remote panel. My tank is in the shop right now getting a new valve and gauge. Your's may be different but I have done quite a bit of looking this is to only set up I have seen on the RV tanks. http://www.rochestergauges.com/Pages/PDFs/6200.pdf The nice thing is the gauge can be changed without draining the tank. The accuracy is probably similar to the gas gauge in most cars, close but not perfect.

Automotive trivia time: There has only been one type of 100% accurate fuel gauge in automotive history. It was a stick with graduations marked on it, which was standard equipment with the model T. (maybe others as well at the time).
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Old 03-18-2013, 08:59 AM   #11
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Automotive trivia time: There has only been one type of 100% accurate fuel gauge in automotive history. It was a stick with graduations marked on it, which was standard equipment with the model T. (maybe others as well at the time).
When my dad owned a service station during my misspent youth, we used a brass (or was it bronze?) dipstick to measure how much was present in the station's bulk storage tanks before and after being restocked, so we could verify the fueler's invoice.

On a propane tank, pouring water over the tank, and looking for the "frost line" that forms at the top level of the liquid propane will tell you accurately how much propane is left in the tank. That can be hard to do with a built-in ASME tank, though. My Interstate has less ground clearance than I would need to get my torso up underneath to check.
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Old 03-19-2013, 12:42 AM   #12
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But don't you have to be using propane for it to chill?
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Old 03-19-2013, 05:16 AM   #13
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But don't you have to be using propane for it to chill?
Temperature of the liquid propane in the tank and vapor pressure of the gaseous propane in the tank are inversely proportional. As long as the vapor pressure is less than 50 psi, the liquid propane will be below 32°F, and there will be a frost line on the tank if you pour water on the side. At vapor pressures higher than 50 psi, the temperature of the liquid propane will rise above freezing, and there will be no frost line.
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Old 03-19-2013, 10:13 PM   #14
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On my Interstate the propane gauge shows full when you fill it and stays that way for some time when you start using it. Also, when the gauge gets to empty there is still a LOT of propane left. IIRC, I get about 20 hours of generator run time from full to empty, then another 6 hours or so after the gauge is reading empty.
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