Propane gauge issues

[Mark Thurlow]

BACKGROUND: I recently and successfully changed from UK Butane to US propane running from US 11lb tanks. For several weeks no issues however albeit in a cooler period - a few degrees above freezing the gas seemed to have run out, cylinders changed over - no issues.

I took the apparently empty cylinder to be filled and the station operator remarked it was less than half used.

Bought a Grilpro inline gauge and fitted it. No propane at the stove with all fittings the same. Remove gauge and all is well. Refitted gauge propane ran for 5 seconds then no propane at stove.

QUESTION

It would appear the gauge is just not passing propane. Am I doing something wrong or have I just been unlucky with a faulty product?

[S/V Illusion]

Two issues - first, every gauge I ever used was not precise, and check the insert pin on the gauge fitting to see if it moves freely.

[john61ct]

In cold weather the pressure fails on small tanks. Factor is surface area not volume, so fatter tanks will get closer to "empty".

Or warm the tanks, hot water or silicone embedded electric elements

Gauges are pretty useless except for the ones that use an internal float.

Weigh the tanks for precision, or just run some warm water along the outside wall. Or buy the scandinavian translucent tanks.

[a64pilot]

It’s not surface area, propane pressure is a factor of the temperature of the liquid propane, that’s it, the colder the lower the pressure.
https://www.engineeringtoolbox.com/p...re-d_1020.html

[Dsanduril]

Pressure is a factor of the liquid propane temperature, but that is a affected by the surface area of the tank. As the propane vaporizes it cools the tank (about 170 BTU/lb at 32F/0C), and the remaining liquid in the tank. That has to be offset by heat applied from outside the tank (just like vaporizing water by boiling), usually by exchange from the air with the surface of the tank. And thus surface area matters. And so does the level of the liquid in the tank, since the surface area of the tank in contact with the liquid is a much more efficient heat transfer than the surface area in contact with the vapor. As the liquid level in the tank drops the heat transfer from the air becomes less efficient.

At static conditions you'll get propane flow at very low temperatures, but as soon as you get flow you start the vaporization process, which lowers the temperature inside the tank. This can lead to reduced vaporization and a drop in propane vapor delivery, eventually (and sometimes it doesn't take very long at all) leading to not enough pressure to push through the regulator.

[pcmm]

Have you checked your solenoid? I've had 2 fail in the last couple of seasons. Never had a problem with propane freezing or refusing to flow even in the dead of winter. Both the types solenoids that failed on me were the type with the inlet inline with the barrel of the solenoid not perpendicular to the body of the solenoid.

[billknny]

Originally Posted by Dsanduril

Pressure is a factor of the liquid propane temperature, but that is a affected by the surface area of the tank. As the propane vaporizes it cools the tank (about 170 BTU/lb at 32F/0C), and the remaining liquid in the tank. That has to be offset by heat applied from outside the tank (just like vaporizing water by boiling), usually by exchange from the air with the surface of the tank. And thus surface area matters. And so does the level of the liquid in the tank, since the surface area of the tank in contact with the liquid is a much more efficient heat transfer than the surface area in contact with the vapor. As the liquid level in the tank drops the heat transfer from the air becomes less efficient.

At static conditions you'll get propane flow at very low temperatures, but as soon as you get flow you start the vaporization process, which lowers the temperature inside the tank. This can lead to reduced vaporization and a drop in propane vapor delivery, eventually (and sometimes it doesn't take very long at all) leading to not enough pressure to push through the regulator.

All that is literally true, and likely comes into place in a place like Alaska with propane tanks outside. But with temperatures "a few degrees above freezing" as the OP stated, it is not even in the realm of possibility unless you are drawing propane at an incredibly high rate. Then you'd have a clue because the outside of the tank would be covered with frost.

[stormalong]

Originally Posted by Mark Thurlow

BACKGROUND: I recently and successfully changed from UK Butane to US propane running from US 11lb tanks. For several weeks no issues however albeit in a cooler period - a few degrees above freezing the gas seemed to have run out, cylinders changed over - no issues.

I took the apparently empty cylinder to be filled and the station operator remarked it was less than half used.

Bought a Grilpro inline gauge and fitted it. No propane at the stove with all fittings the same. Remove gauge and all is well. Refitted gauge propane ran for 5 seconds then no propane at stove.

QUESTION

It would appear the gauge is just not passing propane. Am I doing something wrong or have I just been unlucky with a faulty product?

The way this is worded says to me that you may be confusing the word regulator with the word gauge. Or do you have a defective regulator or defective electric shut off valve?

A gauge is usually set up on a T fitting and has no interaction with the gas flow.

The new (about 20 years now) propane tank valves have an open flow safety cutoff. If the propane is flowing uncontrolled from the tank it will close the valve. Could your installation of the gauge be causing a major gas leak? If so you would hear it and smell it at the gauge.

[a64pilot]

Originally Posted by Dsanduril

Pressure is a factor of the liquid propane temperature, but that is a affected by the surface area of the tank. As the propane vaporizes it cools the tank (about 170 BTU/lb at 32F/0C), and the remaining liquid in the tank. That has to be offset by heat applied from outside the tank (just like vaporizing water by boiling), usually by exchange from the air with the surface of the tank. And thus surface area matters. And so does the level of the liquid in the tank, since the surface area of the tank in contact with the liquid is a much more efficient heat transfer than the surface area in contact with the vapor. As the liquid level in the tank drops the heat transfer from the air becomes less efficient.

At static conditions you'll get propane flow at very low temperatures, but as soon as you get flow you start the vaporization process, which lowers the temperature inside the tank. This can lead to reduced vaporization and a drop in propane vapor delivery, eventually (and sometimes it doesn't take very long at all) leading to not enough pressure to push through the regulator.

Its still temp.
However surface area I still maintain isn’t an issue, to get cooling from the vaporization it’s from pressure drop not surface area. Small flow from small tank and or large flow from large tank.
Then which surface area, tank or propane? I believe you will find a correlation.

When I was much, much younger and dumber, I have used a Rose Bud to heat huge propane tanks enough to get enough flow to run the heaters to heat drilling mud. You do feel strange holding an oxyacetylene torch to a propane tank the size of a truck. Just keep it moving was the idea.

This cooling is of course the operating principle of a vapor cycle cooling system AKA our fridges and or air conditioners, heat pumps.

But reading his post it seems his propane works with gauge not installed, and doesn’t with it installed. What has that got to do with surface are of his tank?

[Dsanduril]

Well, I’m not the only one, check out the information here.

An 11lb tank in high humidity can barely run one moderate capacity stove burner at 70F, much more at low humidity.

Our experience, toward the end of summer we start to see vaporization problems at about 40F in small (20# and smaller) tanks. This is exacerbated with enclosed gas lockers with little air flow. Having said that, under these conditions you should be able to get a stove lit with the static pressure in the tank, it will normally just slow down as the tank cools.

There can also be issues with ice from water vapor, but again, these usually occur over time after gas has been flowing.

[wsmurdoch]

We have a pressure gauge on our propane tanks. It shows the pressure in the tanks which has nothing to do with the amount of propane remaining in the tanks until all of the liquid is gone. Until then the pressure only varies with the temperature of the liquid propane. See the tables and graphs at https://www.engineeringtoolbox.com/p...ix-d_1043.html .

We have a spring scale that was intended to weigh fish that we use to weigh our propane tanks to find out how much propane is in them. The stamp on the tank ring that says something like TW 17.6 lb tells us what the tare (empty) weight of the tank is. Everything above that is fuel. Buy a spring gauge.

The real use for a pressure gauge is to check for leaks. Open the cylinder valve, pressurize the system, close the cylinder valve, then watch the gauge. If it falls, you have a leak. If your solenoid valve was open, you checked the whole system. If it was closed, you checked up to the solenoid valve.

To me it sounds like the outlet valve on your GrillPro gauge is not opening, or the gauge is not opening the outlet valve on your cylinder. Also, feel the bottom of your tank when in use to see if Dsanduril is right and there is just not enough heat entering the cylinder to boil the liquid propane.

[a64pilot]

All that does is quantify the cooling of the liquid due to the heat transfer of the tank, and Is that steel or aluminum tank? Cause that matters quite a lot.
So yes if it’s cold out and you have been running the stove etc for quite sometime you will experience reduced output, but it should never get to the point that the propane doesn’t flow. That is extreme low temps.

[a64pilot]

It’s more likely that his first tank has water vapor in it, and that froze and blocked flow, in colder parts of the world or winter its common for propane suppliers to mix ethyl alcohol into the propane, that of course will mix with the water or water vapor because water and propane do not mix, but water and alcohol does readily, and the mix of course has a much lower freezing point.

[john61ct]

Originally Posted by a64pilot

It’s not surface area, propane pressure is a factor of the temperature of the liquid propane, that’s it

No.

From the "LP-Gas Serviceman’s Manual"

_____
Propane Storage Vessels

The withdrawal of propane vapor from a vessel lowers the contained pressure. This causes the liquid to “boil” in an effort to restore the pressure by generating vapor to replace that which was withdrawn. The required “latent heat of vaporization” is surrendered by the liquid and causes the temperature of the liquid to drop as a result of the heat so expended.

The heat lost due to the vaporization of the liquid is replaced by the heat in the air surrounding the container. This heat is transferred from the air through the metal surface of the vessel into the liquid. The area of the vessel in contact

with vapor is not considered because the heat absorbed by the vapor is negligible. The surface area of the vessel that is bathed in liquid is known as the “wetted surface.”

The greater this wetted surface, or in other words the greater the amount of liquid in the vessel, the greater the vaporization capacity of the system. A larger container would have a larger wetted surface area and therefore would have greater vaporizing capacity. If the liquid in the vessel receives heat for vaporization from the outside air, the higher the outside air temperature, the higher the vaporization rate of the system. How all this affects the vaporization rate of 100-pound cylinders is shown on page 7. It will be noted from this chart that the worst conditions for vaporization rate are when the container has a small amount of liquid in it and the outside air temperature is low.

With the principles stated above in mind, simple formulae for determining the proper number of DOT cylinders and proper size of ASME storage containers for various loads where temperatures may reach 0ºF will be found on pages 7 and 8 respectively.

[Dsanduril]

The heat exchange required to vaporize propane comes from ambient air in pretty much all cases, and the rate of transfer is limited by the heat capacity of air more than tank material or other factors.

Air has a specific heat of about .24 BTU/lb/F. For the OP near freezing ambient temperature that means about 9 BTU/lb are available to vaporize propane (assuming 100% perfect heat transfer) => ~260 cubic feet of air are required to vaporize one pound of propane. A pound of propane is a fair amount, but so is 260 cubic feet of air passing through a gas locker - rail mounted tanks fair better in this regard. And given that heat transfer of 50% would be pretty darn good => at least 520 ft3 of air flow are required to vaporize one pound of propane.

In short, it does not take much to decrease the vapor pressure in a propane tank to the point that it is insufficient to drive the regulator.