What kind of threads are on a propane tank?

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SecondMonkey

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I want to convert a 20# propane tank into an air tank, because they are only $22 at Costco and rated for much higher pressure than a cheap air tank. I know it is common for people to do this. From what I can tell by googling, the threads in the top of the tank for the OPD valve are 3/4"NGT. More googling tells me that is very close to, but not quite the same as 3/4"NPT.

So my question is, can I thread a standard 3/4" NPT pipe fitting into the top of a propane tank? Maybe with lots of teflon tape?
 
I believe on the valve they are Acme threads on the exterior but IIRC the internal thread is left-hand thread and may be AN or other uncommon style so my answer would be "No". Not sure of the threads from the tank to the valve itself though...
 
How much is a cheap air tank already equipped with fill valve, hose,gauge,etc? And what are you going to need more than 100lbs of pressure for? Also, where are you going to fill that has appreciably more than 100psi to begin with?

Bob
 
I just bought a 5 gal portable air tank at Menards for $18. It came with a short air hose, pressure gauge, and shut off valve.
 
Originally Posted By: Crashbox
I believe on the valve they are Acme threads on the exterior but IIRC the internal thread is left-hand thread and may be AN or other uncommon style so my answer would be "No". Not sure of the threads from the tank to the valve itself though...


I should have been more clear...I'm talking about removing the valve and using the threads that are left in the tank.

Originally Posted By: alreadygone
How much is a cheap air tank already equipped with fill valve, hose,gauge,etc? And what are you going to need more than 100lbs of pressure for? Also, where are you going to fill that has appreciably more than 100psi to begin with?

Cheapest air tank around here is $24 at Harbor Freight. Low quality, made in China, 125 PSI max. I don't need the valve, hose, and gauge anyway, that would be tossed. I'd feel much safer standing next to a US made, 375PSI rated, DOT approved tank, wouldn't you? Also the propane tank holds an extra gallon. I can fill it to 200 PSI with my shop compressor, which is like having 12 gallons at 100 PSI.
wink.gif
 
The problem with those "conversion kits" is that I believe they go through the original propane valve, and I don't think that will flow very much. I want to use this mainly as a "surge reservoir" at the end of a 100' air hose so my tools don't choke.

So nobody knows if I can jamb a standard 3/4" NPT fitting in there?

Originally Posted By: benjamming
Your shop compressor is good for 200 psi? What compressor is this?

A converted A/C compressor.
wink.gif
It will actually go up to 300, but I haven't found any air regulators that can handle that.
 
Quote:
A converted A/C compressor. It will actually go up to 300, but I haven't found any air regulators that can handle that.


Now that's interesting. How do you keep ot lubricated?
 
Originally Posted By: Oldmoparguy1
Now that's interesting. How do you keep ot lubricated?

There's an inline air tool oiler on the intake side, and a filter/seperator on the output. I dump the seperator bowl into the oiler as neccessary. :)

Originally Posted By: tom slick
This link might help

http://www.maxquip.ca/pdf/B6.pdf


It looks like NGT and NPT are compatible but NGT has less taper.

Hmmm...that is helpfull...I guess I'll just have to try it out and see.
 
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