The pressure in a propane tank is dependent on the temperature of the tank. Spec D-5 propane has a vapor pressure of 205 psi at 100 degrees F. and propane will boil at -44 degrees F at sea level air pressure. Propane weighs 4.29 pounds per gallon. As the temperature changes the pressure in the tank changes. This is why the pressure style level gauge are worthless and are never right. Good video.
Indeed... but getting into the full Boyles Law chart was a bit much... which is why I just said 40psi vapor pressure at one point even though it has to be pretty cool at that pressure. ;) Another effect of going off the top of the temperature chart is the huge pressures. Tanks have overpressure vents to avoid exploding but I did balloon a 1# tank into a snowman shape when left in my car by accident... scary!
As long as there is liquid in the tank, there will be vapor above it. This vapor is in equilibrium with the liquid with some liquid evaporating and some vapor condensing continuously. The vapor pressure (which is what the "gauges" are really measuring) will show changes based on the average temperature in the tank. Two of the points on the that curve are shown by you above. So, FULL until very near the end. Like you said, a scam.
I just keep my tanks on top of an old scale that I wasn't using. I set my scale to read -16 pounds as the tare weight. I then place my new tank on said scale and it will tell me when I am close to empty.
That works, as long as you're willing to remove your tanks and weigh them frequently. For RV applications, it would be a pain in the tuckus to constantly unbolt tanks to check them, so people devise assorted ways to check in situ. Personally, I go through LP slow enough that just running one tank dry and switching to the other while I refill the 1st provides a reasonably safe window to refill tanks (can find reasonable price to refill before I get worried/desperate enough to pay extreme prices).
Missed review of the sonic ones that stick on the bottom. Reviews say they work pretty good. Might be a new product since you made video. Glad you indicated some tanks come with the gauge. I always assumed those use the pressure as well but apparently you’re saying they use a float which would work pretty well
I agree with this guy that says that weight is the best method. And some propane grill manufacturers have a built in scale. But they are lousy in that they stick in place. Jiggling the tank gets it to move but it just gets stuck in a different place then. I suppose I could get off my lazy ass and take the thing apart and put some lubricant on it. A little gun oil or light oil might do the trick. (don't use thick lube like vaseline because it'll just stick again. ) Yeah, I gotta do that.
Another thing I forgot to mention about the pressure gauges : Many people have reported that they present a significant flow restriction that caused malfunctions in various LP Appliances (stove burning "dirty", heater wouldn't light, furnace issues...). I did another test with my gauge, and there definitely IS a BIG difference in how my large 4-burner grill runs with the gauge installed. I actually DO use my gauge (hey, they fooled me into buying one, even while wondering how it could possibly work), but I keep it on my mosquito killer in my yard -- a VERY slow gas draw that is actually SO slow I can't tell when it stops running, so... the gauge tells me when it's DEAD.
So confused. You mention the float as being a correct solution to measure. Or weight of the tank. I use nothing but 20# tanks. Don’t want to disassemble to tell how much is in my 20# duel tanks. Likely don’t have a float in these generic swap tanks you can get anywhere. So how do I tell, without disassembly ? Maybe use a laser heat temperature gun (now $20 at Amazon) and hot water both? Thanks for posting the video to warn about the generic Walmart gas grill gauge false readings (which I did suspect).
Ah good, mission accomplished if I can confuse you! :-) What I was trying to say was that folks will be happiest by far if they buy the tanks with float gauges built in, since they are about the same cost to buy new. Every once in a blue moon, someone is suckered into swapping a nice gauged tank, but you're still paying triple for the propane at ANY swap station ($20/15lb at swap vs $8 for 18lbs at refill). You CAN get the float valve as a retrofit, but I think it costs almost as much as a new tank (?)... I'd consider a retrofit on my 30# RV tanks since they cost more, but probably still not worth it. On my RV, I go through gas slowly enough that I can swap an empty tank before burning all of the other one, so I don't usually worry about completely running out as much as being curious if I'm starting a trip with the first tank just about to poop out.
If you already have tanks without gauges, the hot water/temperature gun method is a good one -- and you can get them for $7 on AliExpress. While I'm at it, someone GAVE me one of the electronic gas sensors because it didn't work on any of their tanks. I tried 11 tanks of my own, and YEP... not a one could read accurately.
GyroGearloose-HackingRVsCheap - was watching a video about the magnetic gas sensors you put in the bottom of the tank, that has a blue tooth transmitter. Have to do more research on it, and it costs something around $50 (but maybe more). Given I only have 20 pound tanks I can’t justify spending money on a magnetic sensor device that may or may not work. Am more likely to use the laser temperature gun. At least the laser temp gun can be used for ten other tasks (like checking wheels and tires for overheating). And the rule in frugal RV is to only get tools that have multiple uses. Will see.
I'm glad i come across your video. i have an issue. i live in mexico & new to this whole propane usage. & i hate to discredit the station i use (worker just punches the info & it's the company that sets the meters) so, my question, "how do i make sure I'm getting the correct amount?" is there a guage that you recommend on ebay? and do i have them fill the tank & set the guage?
Louie Lou Most tanks are stamped with empty (and sometimes full) weights. From truly empty, an OPD type tank holds 18lbs of LP. Weigh your empty tank and add 18lbs. Non-OPD can take 20, but there's greater risk of over-pressuring/venting with thermal changes.
So, I tried the infrared thermometer. I've been looking for a reason to buy one anyway. I did not notice any appreciable difference between top and bottom. Though it did start off at 75.5, then 75, then 74.5 then 74, and I tried it a few times. I ended up weighing it and determined that I have about 14# of propane left in the tank. I really wanted the infrared thermometer idea to work. How much of a difference in temperature should one notice? My infrared thermometer only discerns by .5 degrees. Having said that, I think I"m going to end up with one of the internal floats in my tank. Anyone using one of those? GyroGearloose mentioned that they would be accurate.
Bruce Mortland I'm guessing you'd still need to use some hot water to create much temperature difference, or do your check at dawn just as the tank starts to heat up in the sun. The float-based gauges shown in the video are pre-installed from Worthington's factory.
The pressure in a propane tank is dependent on the temperature of the tank.
Spec D-5 propane has a vapor pressure of 205 psi at 100 degrees F. and propane will boil at -44 degrees F at sea level air pressure. Propane weighs 4.29 pounds per gallon.
As the temperature changes the pressure in the tank changes.
This is why the pressure style level gauge are worthless and are never right.
Good video.
Indeed... but getting into the full Boyles Law chart was a bit much... which is why I just said 40psi vapor pressure at one point even though it has to be pretty cool at that pressure. ;)
Another effect of going off the top of the temperature chart is the huge pressures. Tanks have overpressure vents to avoid exploding but I did balloon a 1# tank into a snowman shape when left in my car by accident... scary!
As long as there is liquid in the tank, there will be vapor above it. This vapor is in equilibrium with the liquid with some liquid evaporating and some vapor condensing continuously. The vapor pressure (which is what the "gauges" are really measuring) will show changes based on the average temperature in the tank. Two of the points on the that curve are shown by you above. So, FULL until very near the end. Like you said, a scam.
thanks for shearing these information you helped me to understand how it work and how to check properly
very complicated .. I alway have 2 tanks, whene one finish I uese the full one .. thene go and fill the other, thanx
th-cam.com/video/YwYgD9SKPLs/w-d-xo.html
Works for me. You can even share an extra tank with a neighbor.
Thank you for the help..👍🏽
Stick with boiling water. Simple, free and effective. Have never bought a tank with the gauge attached, nor have I ever seen one.
Great information. Thanks.
I just keep my tanks on top of an old scale that I wasn't using. I set my scale to read -16 pounds as the tare weight. I then place my new tank on said scale and it will tell me when I am close to empty.
That works, as long as you're willing to remove your tanks and weigh them frequently. For RV applications, it would be a pain in the tuckus to constantly unbolt tanks to check them, so people devise assorted ways to check in situ. Personally, I go through LP slow enough that just running one tank dry and switching to the other while I refill the 1st provides a reasonably safe window to refill tanks (can find reasonable price to refill before I get worried/desperate enough to pay extreme prices).
Missed review of the sonic ones that stick on the bottom. Reviews say they work pretty good. Might be a new product since you made video. Glad you indicated some tanks come with the gauge. I always assumed those use the pressure as well but apparently you’re saying they use a float which would work pretty well
I agree with this guy that says that weight is the best method. And some propane grill manufacturers have a built in scale. But they are lousy in that they stick in place. Jiggling the tank gets it to move but it just gets stuck in a different place then. I suppose I could get off my lazy ass and take the thing apart and put some lubricant on it. A little gun oil or light oil might do the trick. (don't use thick lube like vaseline because it'll just stick again. ) Yeah, I gotta do that.
Hot tap water works fine to pour on the tank. No need to boil.
So what you're saying is keep your tank where you can pour water on it and save your money
Another thing I forgot to mention about the pressure gauges : Many people have reported that they present a significant flow restriction that caused malfunctions in various LP Appliances (stove burning "dirty", heater wouldn't light, furnace issues...). I did another test with my gauge, and there definitely IS a BIG difference in how my large 4-burner grill runs with the gauge installed.
I actually DO use my gauge (hey, they fooled me into buying one, even while wondering how it could possibly work), but I keep it on my mosquito killer in my yard -- a VERY slow gas draw that is actually SO slow I can't tell when it stops running, so... the gauge tells me when it's DEAD.
So the thing that works must be installed inside the tank. If yours doesn’t have it, you are sh*t out of luck.
Thx
When I say many tanks??? Who are the manufacturers of these tanks? Much appreciate.
I believe the one shown is made by Worthington...
www.homedepot.com/p/Worthington-20-lbs-Empty-Propane-Tank-With-Gauge-308551/300303119
So confused. You mention the float as being a correct solution to measure. Or weight of the tank. I use nothing but 20# tanks. Don’t want to disassemble to tell how much is in my 20# duel tanks. Likely don’t have a float in these generic swap tanks you can get anywhere.
So how do I tell, without disassembly ? Maybe use a laser heat temperature gun (now $20 at Amazon) and hot water both?
Thanks for posting the video to warn about the generic Walmart gas grill gauge false readings (which I did suspect).
Ah good, mission accomplished if I can confuse you! :-) What I was trying to say was that folks will be happiest by far if they buy the tanks with float gauges built in, since they are about the same cost to buy new. Every once in a blue moon, someone is suckered into swapping a nice gauged tank, but you're still paying triple for the propane at ANY swap station ($20/15lb at swap vs $8 for 18lbs at refill).
You CAN get the float valve as a retrofit, but I think it costs almost as much as a new tank (?)... I'd consider a retrofit on my 30# RV tanks since they cost more, but probably still not worth it. On my RV, I go through gas slowly enough that I can swap an empty tank before burning all of the other one, so I don't usually worry about completely running out as much as being curious if I'm starting a trip with the first tank just about to poop out.
If you already have tanks without gauges, the hot water/temperature gun method is a good one -- and you can get them for $7 on AliExpress.
While I'm at it, someone GAVE me one of the electronic gas sensors because it didn't work on any of their tanks. I tried 11 tanks of my own, and YEP... not a one could read accurately.
GyroGearloose-HackingRVsCheap - was watching a video about the magnetic gas sensors you put in the bottom of the tank, that has a blue tooth transmitter. Have to do more research on it, and it costs something around $50 (but maybe more).
Given I only have 20 pound tanks I can’t justify spending money on a magnetic sensor device that may or may not work. Am more likely to use the laser temperature gun. At least the laser temp gun can be used for ten other tasks (like checking wheels and tires for overheating). And the rule in frugal RV is to only get tools that have multiple uses. Will see.
I'm glad i come across your video. i have an issue. i live in mexico & new to this whole propane usage. & i hate to discredit the station i use (worker just punches the info & it's the company that sets the meters) so, my question, "how do i make sure I'm getting the correct amount?"
is there a guage that you recommend on ebay? and do i have them fill the tank & set the guage?
Louie Lou Most tanks are stamped with empty (and sometimes full) weights. From truly empty, an OPD type tank holds 18lbs of LP. Weigh your empty tank and add 18lbs.
Non-OPD can take 20, but there's greater risk of over-pressuring/venting with thermal changes.
So, I tried the infrared thermometer. I've been looking for a reason to buy one anyway. I did not notice any appreciable difference between top and bottom. Though it did start off at 75.5, then 75, then 74.5 then 74, and I tried it a few times. I ended up weighing it and determined that I have about 14# of propane left in the tank. I really wanted the infrared thermometer idea to work. How much of a difference in temperature should one notice? My infrared thermometer only discerns by .5 degrees. Having said that, I think I"m going to end up with one of the internal floats in my tank. Anyone using one of those? GyroGearloose mentioned that they would be accurate.
Bruce Mortland I'm guessing you'd still need to use some hot water to create much temperature difference, or do your check at dawn just as the tank starts to heat up in the sun. The float-based gauges shown in the video are pre-installed from Worthington's factory.
Actually... propane will find it's equalizer..if you have a working gauge..home Depot..Lowe's ace hardware your good...simple