Not quite out of gas

[jcornell]

Neophyte question here.

I'm on tank #2 for my home-built propane forge. I'm using the usual 20# tank (thank you, Propane Taxi) which goes along swimmingly, until the gas pressure drops from whatever I've been using to about 5 psi - where the flame is weak and sputtery.

At this point, how long will it burn before it's totally out of gas? Forge welding is out of the question at this point, as is any serious heating of metal greater than 1/4 inch in diameter.

[Toreus]

When the propane pressure drops on my setup, it's usually because it's frozen rather than empty. Although it does get worse when you have little propane left. Putting the LP tank in a water-filled container that goes about 1/2 to 2/3 of the way up the tank usually warms up the LP enough so that it starts evaporating again.

Hope this helped!

EDIT:

As to how long a propane tank lasts, it really depends on the forge: big/small, insulated/not ...
I run a blown forge and I managed to tune in to run at <1psi for a 1/16 fuel port.

[Naz]

I used to keep two 20 pound tanks and switch them around whenever one would freeze up.
Now I have a 100 pound, 60 pound and three 20 pound tanks.( Yeah you could say I'm a bit insecure).
The bigger tank is a good solution for this problem and keep the 20 pound tank for back up.
There's a lot of info on this site as to why the tank freezes and other solutions also.

Naz

[ThomasPowers]

In the hot summers here in NM I can take a tank down till it's pretty well *dry*. In the winters I generally have to either warm the tank or switch it out when there is still a gallon or so left in it---since I always buy propane by the gallon there's no extra cost in doing it this way. If you just trade bottles instead of refilling you'd lose a lot of money switching before it was "dry". (Also the "trade" is about $7 more than a refill and my local re-fill place has a frequent buyer card where for every 5 refills I get a free one!)

[Dodge]

I have never used a 20#er but when my 100#er gets low, the flame just seems to peter out gradually. IIRC I have a similar setup to Toreus. (Blown with 1/16" orifice) but in a 1.25 pipe. I run at very low pressure; 1 - 3 psi as a rule so when it goes down, I'm pretty sure its "M T" In my previous forge with two Reil EZ burner inspired burners that ran on higher pressures; at least 5 - 7 psi, there was considerable fluctuation in the output when the gas was running out. As for how long, I would have to say it was a matter of minutes when the fluctuation would begin. Once it started; and even when the blown flame starts to dwindle, I know I might as well start sweeping up as I'm not even going to finish the heat I'm currently on. My biggest concern is knowing just how much is in the tank at any given level. The 100#er in my experience just doesn't frost up letting you know where the level is except only in the warmest humid times. Otherwise, there just isn't much if any temp diff from the fuel level up or down. This begs the question, 'how do you guys tell the level of your 100#er??'

Scott

[DennisG]

Dodge, visit http://ronreil.abana.org/design2.shtml.

Go down to the BTU output calculator and the other docs to go with it. Down load that and it will help you since it has a section that also calculates how much time a certain sized bottle will last. I have a #60 (0.04")orifice and a 20lb tank. I use a middle coefficient of .67, and 8psi. The calculator says I should get 8.14 hrs out of my tank.

Since I turn my gas down when pounding big things and such I figure I will get closer to 10 hrs a tank.

Hope this helps.