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Thread: where to cut 20lb lp tank

  1. #1
    Boolit Bub
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    where to cut 20lb lp tank

    got my 20 lb lp tank dug out, hadn't seen it in 10 yrs............ lol. valve was open all this time so so shouldn't be no fire risk. could somebody tell me wheres the best place height wise to cut it. plan on makin a bottom pour. cutting isn't a problem but nothing like experience making a pot. all tips / help is greatly appreciated. got a 200k burner with wind screen on 3 sides.
    once again just bob
    I BELIEVE IN JOHN 3:16

  2. #2
    Boolit Master MyFlatline's Avatar
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    Most cut just above the weld for a smelt pot, not sure about a bottom pour. A word of caution, remove the valve. Do not trust that the tank is empty just because it was open, I don't recall when they started using the safety valves.

  3. #3
    Boolit Master

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    Most of the ones that I have seen were cut right at the seam. Either above or below it. For safety, remove the valve and flush it with water. Please do not blow yourself up!

  4. #4
    Boolit Master

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    I saw a video where the user broke up dry ice and placed it in the tank after removing the valve. The carbon dioxide gas displaced any other gas including oxygen there by preventing any danger of explosion
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  5. #5
    Boolit Master
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    Pull the valve, fill with water, drain, cut.

  6. #6
    Boolit Master Moleman-'s Avatar
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    I used water to make sure any gas was out. There was also an oil sludge at the bottom that stunk of the smell they put in propane and NG to make it detectable.

  7. #7
    Boolit Master
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    That smell is some version of a Mercaptan, whatever they use (Likely an Ethyl Mercaptan but could be another.) IIRC it's the same molecule basically as an Ethanol, only the Oxygen is replaced with a Sulfur atom. Made it in high school, it's commonly called "Skunk Oil" or the like as it's the active part of skunk spray...

  8. #8
    Boolit Master
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    Plus +1 on removing the valve and filling the tank with water and draining BEFORE cutting it.
    In fact, after draining the water I would leave it out in the sun for a day or two with the valve off the tank.

    The ones I have cut had a slight overlap between the two tank halves where the weld is located. Cutting at the weld results in cutting through twice the material, cutting slightly above or below the seem (maybe 3/8" ? ) gets you back into the single layer material and is easier.

  9. #9
    Boolit Master redhawk0's Avatar
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    I cut 1.5" above the weld line. This gave me that last 1.5" to attache a steel rod handle. I used a diamond wheel on my 4.5" grinder.

    redhawk

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  10. #10
    Boolit Master

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    If you cut right below the top weld, your pot will hold every bit of 500 lbs. As mentioned earlier, remove the valve and fill it with water or run an airhose in it for a while to clear all the propane residue from the tank.
    Scott

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  11. #11
    Boolit Man



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    For those who add a valve to make the tank a bottom pour - what kind of valve did you use that will stand up to the heat from a turkey fryer burner?

  12. #12
    Boolit Master
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    I fill with water then drain just enough to give air space for using the plasma cutter.
    If you have ever worked with gas tanks, you learn to be careful. Tanks that have been empty for ten years can still have enough fumes to go off.

  13. #13
    Boolit Bub
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    yea I welded for 40 years for myself and friends. thanks everybody for all your help. its appreciated.
    bob
    I BELIEVE IN JOHN 3:16

  14. #14
    Boolit Bub
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    redhawk, where did you buy that bail handle....
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  15. #15
    Boolit Master redhawk0's Avatar
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    Quote Originally Posted by BCOWANWHEELS View Post
    redhawk, where did you buy that bail handle....
    Its just a 3/16" diameter steel rod that I bent by hand....the grip portion is just a spring that I cut the hooks off of. Both parts were bought at Lowes for about $5 One mistake I made was that I heat treated my pot in a fire before I used it for the first time...I guess heat treat isn't really the correct term here..my goal was to burn off the epoxy paint on the tank...but that fire took the temper out of the spring. So...if you do try to get the epoxy paint off....burn it off before adding the bale handle and spring.

    Here you can see it lost the temper.

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    redhawk

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  16. #16
    Boolit Master

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    I truly recommend you pull the valve and fill several times with soap water and agitate some to help clean out any residues before cutting. If a tank blows when cutting it can be fatal or result in serious injuries. Another trick is to keep the tank purged with a air hose while cutting. Push a air hose into the tank from compressor and open regulator to 20-30 psi and let it flow. This keeps any residual fumes from building up in the tank.
    Ive cut mine with a hack saw and fine blade 32 tpi working around the tank. this doesnt produce sparks when cutting and no sparks from an electric motor. This gives a nice fine cut that finishes easily.

    Decide where you want to cut your tank height wise and lay out. Put a couple wraps of 2" masking tape around th e tank so it is flat and wrinkle free with the edge where you want the cut. The tape laid flat gives a square edge to follow with the saw as you work around it. It takes a little longer to break thru to the inside when starting the cut but once thru and working around it cuts pretty quick. ( I think mine was around 45 mins for each cut ). I also remove the original bottom stand and cut a 3-4" ring from the tank to weld on for a full dia stand on the tank. This gives a better foot print for the tank and acts as a heat shield holding the heat in around the pot.

    Most valve for pots are a simple sliding type valve with seat and shaft. a angle is machined for the seat at 45* in the seat with the appropriate sized hole thru ( on a smelting pot a 1/4"-3/8" hole thru would pour pretty quick) 1 1/4" hole with seat would put the seat dia around 1" a shaft the need length 1" in dia is the machined with a 3/16" stem 1" long ( I also turn this at a 10* angle to allow more area for flow when open) and the mating seat angle above that. the stem keeps the rod in the spout and the seats seal it. After machining the seats are lapped together for a good seal.

    Using a domed bottom propane tank the valve will need to be in the center and be right above the burner making access harder. a pipe tank with flat bottom angled to one edge would put the spout on the edge of the pot and more accesable. One thing to do is make a mock up of the valve and handle from card board and see how it looks.

  17. #17
    Boolit Master Grmps's Avatar
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    "Push a air hose into the tank from compressor and open regulator to 20-30 psi and let it flow. This keeps any residual fumes from building up in the tank."

    They used to wield gas tanks this way.

    I'm for shooting a hole in the top, those valves ca be a ##### pain to remove

  18. #18
    Boolit Master redhawk0's Avatar
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    I closed my valve, hit the top safety cage welds with the grinder (not breaking through the tank) then knocked off the safety cage with a 3 lb hammer. Once the cage was removed...I opened the valve all the way up, and proceeded to hit the tank valve on the side so it unscrewed CCW. It came loose with about 5 whacks...then used a pair of channel lock pliers to unscrew it the rest of the way. Filled with water, drained and left overnight upside down (used the safety cage to hold it)...since gas is heavier than air...it just sinks out the bottom..I've been told I over-did the safety thing by doing this multiple times over a two week period...but I didn't want to have any personal or property damage...so I was happy to be over-cautious.


    redhawk

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  19. #19
    Boolit Man



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    Quote Originally Posted by country gent View Post
    Most valve for pots are a simple sliding type valve with seat and shaft. a angle is machined for the seat at 45* in the seat with the appropriate sized hole thru ( on a smelting pot a 1/4"-3/8" hole thru would pour pretty quick) 1 1/4" hole with seat would put the seat dia around 1" a shaft the need length 1" in dia is the machined with a 3/16" stem 1" long ( I also turn this at a 10* angle to allow more area for flow when open) and the mating seat angle above that. the stem keeps the rod in the spout and the seats seal it. After machining the seats are lapped together for a good seal.
    Could you include a pic of the valve you made. I have no access to any machining tools or lapping tools.

  20. #20
    Boolit Master
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    Quote Originally Posted by dsh1106 View Post
    If you cut right below the top weld, your pot will hold every bit of 500 lbs. As mentioned earlier, remove the valve and fill it with water or run an airhose in it for a while to clear all the propane residue from the tank.
    If your pot holds 500# it was bigger than a 20# tank. I just did one, cut about 1/2" above the weld. First load I did in it was four foundry ingots of 62-63# ea. Those filled it to right about the weld line with very close to 250#.

    I made a couple valve wrenches after I saw a commercial one, one for regular valves and one to remove the valve on a plumbers pot tank. Opening the valve to drain the tank may not empty it, the valves in use now have a high flow shutoff and won't let gas out rapidly. To get the tank empty you should open the bleed valve located on the left side when facing the outlet. It is a slotted screw recessed into the valve casting, you can hear gas escaping if there is any in the tank. I had one that had a bad valve and the gas guy told me that was the only way to get it empty, took about three days with it sitting in the middle of a five acre field.

    To get rid of the stink quickly after I remove the valve I first fill it to overflowing with hot water then I dump about half the water out and add a bunch of TSP. The the tank goes on the burner and after I screw a 3/4" street elbow with a short section of pipe attached(keeps the boiling water/steam from blowing straight up) I bring it to enough of as boil to rock the tank. 10 minutes of that the stink is gone and you are assured there is nothing flammable left in that tank.

    I have cut several tanks now, two for smelting pots and three more, that I cut at the top of the straight section, for use as "hot buckets" to throw the 700 junk into as it gets skimmed of the smelt.
    Last edited by Alan in Vermont; 07-07-2018 at 11:25 AM.
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