Heater/Propane question

mattaxelrod

mattaxelrod

Pre-takeoff checklist
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Matt
I use one of those hot air blower heaters to warm the engine. I attach a small canister of propane, start the fan, and ignite.

I can never seem to use all the propane in the canister. The temperature of the heater starts to go down--I can gently tilt the canister a bit, but then I have to be careful of flareups. I know there's more in there, because after I turn the whole thing off, I can hear more liquid propane sloshing around in there. I think I end up using about 3/4 of every canister.

Anyone know why?
 
mattaxelrod said:
Anyone know why?
Click to expand...

Yes...the propane is liquid in the can, the liquid vaporizes and moves out of the can to the burner tip, as the liquid vaporizes it cools the remaining liquid which in turn lowers the liquid's vapor pressure. Eventually, not enough vapor is produced to support the flame. You can warm the can and help out. Be careful.
 
Possibly your heater requires a substantial amount of propane pressure in the tank to function. When it gets below that pressure level, it shuts off. What's left might run a camping grill or stove, but isn't enough for your heater.
 
Actually, I did try using one of the big 20 lb tanks a number of years ago. I found that when the tank got really cold sitting out in the winter, I didn't get a good flow of propane, so I ended up with the same problem.

Thanks for the explanations--it's pretty much what I figured but wanted to make sure.
 
Clark1961 said:
Yes...the propane is liquid in the can, the liquid vaporizes and moves out of the can to the burner tip, as the liquid vaporizes it cools the remaining liquid which in turn lowers the liquid's vapor pressure. Eventually, not enough vapor is produced to support the flame. You can warm the can and help out. Be careful.
Click to expand...

Very clear explanation--thanks. This is also undoubtedly why the outside of the canister frosts up after a certain period of time.
 
I use a heater that fits in a toolbox. The propane is in the box near the heater ,keeping the tank warm,giving a better flow.
 
Propane boils at -44°F and must be able to absorb enough ambient heat to compensate for the boiling process. The bigger the cylinder, the warmer it is outside, the warmer the cylinder is kept will lessen the chance of cylinder freeze up. If a frost line forms around the cylinder at the level of the fuel, this is a sign that the cylinder is being over worked and is in the process of freezing up. The longer you run the oversized load, the lower the vapor pressure inside the cylinder will be. I ran a 30-60,000 btu/hr heater on a 20 lb cyl in a 55F hangar down to -35F cyl temp the other day. It finally shut down on the flame proving sensor. Did it for fun to see how cold it would get . The pressure inside the cylinder was about 3 psig at shut down. A typical 20 lb cyl is only good for about 22,700 btu/hr at 55F. I have a 30 lb now, so I am good for about 30,100 btu/hr. A heating pad or electric blanket can be used to keep your tank warm. If exhaust is used, make doubly sure you have no gas leaks and monitor tank temperature.
 
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