Capacity Indicator - Propane Gas

[eliasurbina]

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.

[Inland RV Center, In]

Originally Posted by eliasurbina

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

[eubank]

Can't tell you about your indicator for sure, but for all other uses I know of, full means full to capacity (80%).

Lynn

[Protagonist]

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.

[dznf0g]

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.

[Protagonist]

Originally Posted by dznf0g

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.

[73shark]

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.

[Smartstream]

Originally Posted by Protagonist

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.

[Protagonist]

Originally Posted by 73shark

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.

[dznf0g]

Originally Posted by Smartstream

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).

[Protagonist]

Originally Posted by dznf0g

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.

[73shark]

But don't you have to be using propane for it to chill?

[Protagonist]

Originally Posted by 73shark

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.

[russ240]

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.

[idroba]

Originally Posted by Protagonist

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.

A cup of very hot water poured down the side of the tank, then wait 20 seconds or so, run your hand down the tank and you will feel where the warmer Aluminum meets the colder metal. That is the line of the liquid in the tank, and this works fine in any weather, warm or cold.

[73shark]

Originally Posted by Protagonist

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.

Just like freon. As soon as you start charging an A/C system, the bottle or can starts to get cold and on a humid day, a sweat line will show where the liquid is. Which is why I store partial cans in a freezer and lower the vapor pressure and slows down the leak rate against the rubber seal on the tapper valve.

I suspect on a normal summer day, the only way the propane vapor pressure is below 50 psi is if the propane is being consumed.

[Boxster1971]

My LPG tank didn’t read full on my Interstate when I had it filled. But there is some misinformation in this tread. The TouchSensor system doesn’t use the transducers for the LPG tank. They only work on plastic tanks. From the TouchSensor spec sheet: “NOTE: TouchSensor does not supply the LPG sensor. SensaTank RV100 reads the signal supplied from the OEM LPG tank.”

[Protagonist]

Originally Posted by Boxster1971

From the TouchSensor spec sheet: “NOTE: TouchSensor does not supply the LPG sensor. SensaTank RV100 reads the signal supplied from the OEM LPG tank.”

Good info. Thanks. I would have known that if my Interstate's owner's manual packet had included a Touchsensor spec sheet.

I went to the Touchsensor web page looking for a spec sheet or owner's manual, but none of the models shown on the web page matches the display panel that is mounted in my Interstate. I wonder if mine is an older model that's been phased out?

Oddly enough, mine also seems to be a 120vAC system, too. It doesn't work unless I am plugged into shore power, I'm on generator power, or have the inverter set to Auto/Invert. If I'm just on DC power, the only display that works on the Touchsensor panel is the house battery voltage; the tank level displays and the main battery voltage won't work on 12vDC house power. Weird.

Side note, I sure wish they'd have put a second black/gray tank display panel right next to the macerator pump controls, so I wouldn't have to go back inside just to verify the tank levels before reeling up the discharge hose.

[wayneskid]

Originally Posted by Protagonist

Good info. Thanks. I would have known that if my Interstate's owner's manual packet had included a Touchsensor spec sheet.

I went to the Touchsensor web page looking for a spec sheet or owner's manual, but none of the models shown on the web page matches the display panel that is mounted in my Interstate. I wonder if mine is an older model that's been phased out?

Oddly enough, mine also seems to be a 120vAC system, too. It doesn't work unless I am plugged into shore power, I'm on generator power, or have the inverter set to Auto/Invert. If I'm just on DC power, the only display that works on the Touchsensor panel is the house battery voltage; the tank level displays and the main battery voltage won't work on 12vDC house power. Weird.

Side note, I sure wish they'd have put a second black/gray tank display panel right next to the macerator pump controls, so I wouldn't have to go back inside just to verify the tank levels before reeling up the discharge hose.

My LPG monitor seems somewhat erratic but it does occasionally display as full even when I know it is not. FWIW, I see this comment on page H-17 of my Interstate Owners Manual; I haven't tried to make this adjustment:
"The fluid tank monitor system has been calibrated at the TouchSensor factory for the size tanks the Interstate uses and should never need another calibration. On the rear of the monitor panel there is an adjustable potentiometer to manually adjust the monitor panel reading of the LPG tank level, this is set at the Airstream factory for the tank on the Interstate motorhome and needs no further adjustment."

As for your panel being fully functional on AC only, I'm pretty sure mine shows all level indicators regardless of power configuration, as long as the battery disconnect is ON. I can check this the next time I'm where my Interstate is garaged.

[Boxster1971]

I also thought my tank monitor panel was also only working on 120V AC, but then I noticed it was erratic on any power source while in Florida last month. Now it doesn’t work at all. Just got back from a trip to Bay City, Michigan and I’ll start trouble shooting what I hope is just a bad switch. My dealer in Colonial in NJ and I’ll give it a shot to fix myself before I trek up to NJ for warranty work. So far I’.ve metered the pins on the connector and it is definitely a 12v DC system.
The Airstream owner’s manuals and other technical data are woefully inadequate compared to the competition. Winnebago has great info on all their models that makes the engineer in me jealous.
- - Mike
2013 Interstate Lounge EXT