Not again!

[PSOUZA]

Originally Posted by WileyOne

You are correct. You read it right and I read it wrong. After reading a second time, I think the valve he was turning was at the tank.

Still, the concept is the same. I have never seen liquid propane because it changes to a gas faster than my eyes can observe. If it was liquid, it was almost definitely water.

I have serious doubts what the OP saw was liquid propane as well. The description of the event was so lacking in detail as to be useless in any analysis.


Had the OP said that the handle of the valve was frosted over or "very cold to touch" then I may think differently.


If you have ever seen liquid propane escape from a poor connection during a fill operation, or even cracked the valve on a small propane cylinder and seen the vapor (white mist) escape then you have seen that propane does NOT turn to gas faster than the eye can see.


Science is pretty exact when it comes to "How Things Work".
Words mean things!



True that you never saw the "liquid" propane.


The white vapor that you saw was not "Gas". It was vapor, which is combination of gas, and a mist of liquid propane still in the liquid state. Because the heat loss of evaporation has slowed the conversion to the gaseous state, the process takes time and is observably NOT instantaneous.


During the time, while it was visible, it was absorbing heat, from the air, and converting to the final state of "Gas".


During the visible "vapor" state, the propane completes the final stage where it expands 270 times the original liquid state, into the invisible gaseous stage.


So if you, or any one else has seen the white vapor, you prove the claim that propane does NOT flash to gas instantaneously, or "faster than the eye can see.

Additionally. if one were to physically slow down the flow of vapor, at atmospheric pressure, in a confined space, it is entirely possible to lower the temperature of the vapor to a point where liquid propane will condense. It is a standard laboratory practice.




Phil

[Todd727]

Originally Posted by daveandcarol

So if the propane turns to liquid at -40 degrees F and they fill the tank under enough pressure to make it liquid, why isn't the tank covered with frost? I know, it would naturally liquify at that temperature. Filling the tank forces it to liquify due to the pressure. So what kind of PSI is that propane at when the tank is filled? Example: IIRC, an oxygen tank for welding is either 300PSI or 600PSI when full (I can't remember, it's been a while), so what is propane?

O2 tanks are 2200 psi. Acetylene is 250 psi

[LargeMarge]

Originally Posted by Quickuc

[edited for brevity]
...I had our RV repair place add 3.5 pounds of propane to the tank. Went out this morning to fire up furnace,so I turn valve on tank to open and liquid came shooting out around the knob I was turning. So I closed it, and opened it again, all the way this time and it went to a drip. Did they over fill it?...

A couple points:
a == Propane weighs a squidgeon over four pounds per gallon, so you purchased about 3.5 quarts.

b == Tank orientation == we foraged a side-mount frame-mount tank from a campground Dumpster©®™ after the tweekers freaked after they set it on the bottom ring, then fired their camp-stove... only to run screaming in circles because they were burning liquid fuel instead of gas vapor.

We used the tank as designed == on its side == for decades. At fill stations, we explained "the tank is off our forklift, so it's exempt from cert limits". Nodding helps, as does a tip to the filler. Frequently, fillers pointed to the stamped date == May 1947 == and nodded right back at us.

c == Watching fillers and asking about the procedure, we learned modern propane tanks == at least from May 1947-to-current == have an overfill vent on the valve. Before filling, the filler slightly opens the overfill, proceeds to fill until vapor escaping from the overfill valve indicates the tank is as full as it can get, then the filler shuts the overfill valve while closing the fill lever on the fill hose.

From my observations, most modern tanks seem engineered to not be overfilled. Like the diesel tank on your truck, propane tanks hold only so much. More is not better.

Our suggestion == ask some RV repair places. Averaging their answers should give a happy median ratio you can live with. Or swap the tank at a propane tank exchange. Or go all-electric. Or return to the ancient ways of our ancestors.. add another layer of fleece.

[PSOUZA]

Quote:
Originally Posted by daveandcarol
So if the propane turns to liquid at -40 degrees F and they fill the tank under enough pressure to make it liquid, why isn't the tank covered with frost? I know, it would naturally liquify at that temperature. Filling the tank forces it to liquify due to the pressure. So what kind of PSI is that propane at when the tank is filled? Example: IIRC, an oxygen tank for welding is either 300PSI or 600PSI when full (I can't remember, it's been a while), so what is propane?

Originally Posted by Todd727

O2 tanks are 2200 psi. Acetylene is 250 psi

Neither of these gases should be compared to the LPG group. They have nothing in common. Acetylene is stored dissolved in acetone because acetylene is unstable in its liquid phase at vapor pressure. It can detonate on impact.


I see some more confusion regarding how propane "works" and is packaged.


Unlike oxygen which must be cooled to a liquid state and then stored in a special cylinder at 2000+ llbs. Propane can assume the liquid state simply by pumping the gas into a cylinder. The gas, just like air will heat under compression, but it will liquefy. This method requires measures to control heating from compression.In small quantities, propane can be compressed into liquid without concern for heat. The refrigerated propane liquid has the same characteristics as the compressed version and can be stored in the same type cylinder. Eventually it does reach ambient temperature. Both methods must leave room for liquid expansion. 20% head room.

Oxygen can not, will not liquefy by compression. It must be cooled to liquefy.

Either processes end result is liquid propane storage at ambient temperature. The container must be certified for the peak pressure the liquid may encounter if exterior temperatures rise. Typical storage pressures range approximately from 40 to 250 lbs. depending on temperature.

The frost starts when fuel is drawn from the tank and the propane begins to boil along the tank boundaries. The heat that the vapor conversion requires must be replaced and is drawn from the tank wall and from the surrounding air. The tank drops to below freezing **and moisture in the air freezes on the outside of the tank as frost.


** Butane users take note.


The tanks are rated to 320 lbs. Approx. A safety "pop off" valve is incorporated into the tank to relieve pressure in event of over temperature / over pressure.


Phil

[twinboat]

Originally Posted by LargeMarge

A couple points:
a == Propane weighs a squidgeon over four pounds per gallon, so you purchased about 3.5 quarts.

b == Tank orientation == we foraged a side-mount frame-mount tank from a campground Dumpster[emoji767][emoji768][emoji769] after the tweekers freaked after they set it on the bottom ring, then fired their camp-stove... only to run screaming in circles because they were burning liquid fuel instead of gas vapor.

We used the tank as designed == on its side == for decades. At fill stations, we explained "the tank is off our forklift, so it's exempt from cert limits". Nodding helps, as does a tip to the filler. Frequently, fillers pointed to the stamped date == May 1947 == and nodded right back at us.

c == Watching fillers and asking about the procedure, we learned modern propane tanks == at least from May 1947-to-current == have an overfill vent on the valve. Before filling, the filler slightly opens the overfill, proceeds to fill until vapor escaping from the overfill valve indicates the tank is as full as it can get, then the filler shuts the overfill valve while closing the fill lever on the fill hose.

From my observations, most modern tanks seem engineered to not be overfilled. Like the diesel tank on your truck, propane tanks hold only so much. More is not better.

Our suggestion == ask some RV repair places. Averaging their answers should give a happy median ratio you can live with. Or swap the tank at a propane tank exchange. Or go all-electric. Or return to the ancient ways of our ancestors.. add another layer of fleece.

A few point on your points.

Its a fixed ASME tank. Bolted to the chassis. They are filled by the gallon not weight. Unless he had the RV on a scale, he got his propane by the gallon.

The bleeder that is opened does not prevent overfilling. It only indicates that its at 80% capacity. Its up to the filling person to stop the flow, otherwise he can overfill it, if older then 1984.

ASME tanks, since 1984, have had an actual overfill protection device " OPD " installed. The attendant is still supposed to monitor the 80% valve, but the OPD will stop overfilling.

You don't " SWAP " chassis mounted motor home tanks.

[Todd727]

Originally Posted by PSOUZA

Quote:
Originally Posted by daveandcarol
So if the propane turns to liquid at -40 degrees F and they fill the tank under enough pressure to make it liquid, why isn't the tank covered with frost? I know, it would naturally liquify at that temperature. Filling the tank forces it to liquify due to the pressure. So what kind of PSI is that propane at when the tank is filled? Example: IIRC, an oxygen tank for welding is either 300PSI or 600PSI when full (I can't remember, it's been a while), so what is propane?




Neither of these gases should be compared to the LPG group. They have nothing in common. Acetylene is stored dissolved in acetone because acetylene is unstable in its liquid phase at vapor pressure. It can detonate on impact.


I see some more confusion regarding how propane "works" and is packaged.


Unlike oxygen which must be cooled to a liquid state and then stored in a special cylinder at 2000+ llbs. Propane can assume the liquid state simply by pumping the gas into a cylinder. The gas, just like air will heat under compression, but it will liquefy. This method requires measures to control heating from compression.In small quantities, propane can be compressed into liquid without concern for heat. The refrigerated propane liquid has the same characteristics as the compressed version and can be stored in the same type cylinder. Eventually it does reach ambient temperature. Both methods must leave room for liquid expansion. 20% head room.

Oxygen can not, will not liquefy by compression. It must be cooled to liquefy.

Either processes end result is liquid propane storage at ambient temperature. The container must be certified for the peak pressure the liquid may encounter if exterior temperatures rise. Typical storage pressures range approximately from 40 to 250 lbs. depending on temperature.

The frost starts when fuel is drawn from the tank and the propane begins to boil along the tank boundaries. The heat that the vapor conversion requires must be replaced and is drawn from the tank wall and from the surrounding air. The tank drops to below freezing **and moisture in the air freezes on the outside of the tank as frost.


** Butane users take note.


The tanks are rated to 320 lbs. Approx. A safety "pop off" valve is incorporated into the tank to relieve pressure in event of over temperature / over pressure.


Phil

No one compared anything, well, until you did. He asked about pressure and then related that to what he knew about welding. His numbers were wrong, so I gave him the correct number for O2. I gave him the number for C2H2 because that may be why he had a lower number in his head.


I full well understand the process of filling a C2H2 cylinder and am also aware of the dangers of excessive draw rates.

[KanzKran]

Originally Posted by PSOUZA

The tanks are rated to 320 lbs. Approx. A safety "pop off" valve is incorporated into the tank to relieve pressure in event of over temperature / over pressure.

According to the PERC, it's either 250 or 312 psi service pressure, per the nameplate that's supposed to be permanently affixed to every ASME tank installed in an RV. Pressure relief valves are 375-400 psi cracking pressure, depending on the style and use. I think 375 is standard for DOT cylinders, but I'm not positive about that.


I should add that I think the design factor used on propane tanks and cylinders is 4:1 on service pressure, but I can't be sure. So a 240 psi 'standard' 20 lb gas grill cylinder would have a burst pressure of at least 960 psi, if that's true.

[KanzKran]

Originally Posted by WileyOne

It is near impossible to fill a propane tank to 100% with liquid propane using conventional equipment, so we can expect anything that comes out of that tank to be in the gaseous state.

One exception being if the OPD failed, which it certainly can since it's a mechanical device, it could be filled full or near full. Should the ambient temperature increase, liquid propane will expand at a rate of about 17 times that of water, and could expand enough to fill the void completely, at which point pressure will shoot up with only small increase in temperature.

Filled to 80% of capacity at 0 deg. F, then heated to 125 deg. F, it would expand to fill the tank to 100%. Which is obviously why the 80% max fill figure is used - a minimal chance of overfill from expansion resulting in relief valve operation and venting. But if it's filled somewhat more than 80%, the expansion headroom decreases and venting starts at a lower increase in temp from original fill temp.

[lwmcguire]

You can see the liquid level line on most bulk tanks or feel the temperature difference when filling or drawing them down at a high rate

The temperature does make a huge difference and why most tanks are white or grey

RV MH tanks are out of direct sunlight typically so not as much change

Used to run tractors and pickup trucks on propane for over 30 years with some trucks dual fuel and others with propane crabs

They all had heat exchangers to convert the liquid to gas

Propane can sneak up on you so be careful

One nice thing is propane leaks usually seek lower elevations which helps if the leak is outside the MH

[3Ds]

One of my 30 gal propane tanks on my 2014 Dutchmen Voltage 3605 TH has a variable "ring" or "singing" off key when using the furnace. I haven't noticed the noise when using the oven. I'm sure the furnace uses a lot more volume than the oven so it flows more. Any thoughts.

[twinboat]

Originally Posted by 3Ds

One of my 30 gal propane tanks on my 2014 Dutchmen Voltage 3605 TH has a variable "ring" or "singing" off key when using the furnace. I haven't noticed the noise when using the oven. I'm sure the furnace uses a lot more volume than the oven so it flows more. Any thoughts.

It's probably the regulator making it sing as the gas flows thru it.

Inside the regulator is a diaphragm and needle valve that constantly move while controlling the gas flow.

[KanzKran]

Originally Posted by 3Ds

One of my 30 gal propane tanks on my 2014 Dutchmen Voltage 3605 TH has a variable "ring" or "singing" off key when using the furnace. I haven't noticed the noise when using the oven. I'm sure the furnace uses a lot more volume than the oven so it flows more. Any thoughts.

Originally Posted by twinboat

It's probably the regulator making it sing as the gas flows thru it.

Inside the regulator is a diaphragm and needle valve that constantly move while controlling the gas flow.

My Weber gas grill does exactly that when all three burners are at max. I’ve always assumed it was the regulator. Less than max flow rate and that faint sound stops.

[3Ds]

thanks KK and TB. Ill replace the regulator, it is 5 yrs old anyway.