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Air tight bungs and caps

LoneGunman

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Mar 27, 2007
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2,081
Location
The Gunshine state
I'm building a pressure assisted blaster. For my abrasives fill hole I tried using a 2" galvanized pipe coupling as the bung. I welded the bung to the top of my tank, no matter what I try I get air leaks. At first I thought I warped the first one, so I made sure the second was welded slowly and kept cool. That one still leaked. then I tried a 2" -1 1/2 reducer as a bung, still have the same problems. Lastly I tried a ****** as the bung and use a female cap, once again, it still ^&*(*&%$ leaks. I tried pipe dope and teflon tape, still leaks.

WTF am I doing wrong? It's driving me crazy because I have ZERO leaks in my air lines, my air system has held air for over a week without kicking on. I only need this thing to hold 7-10 PSI's.

I asked on the message board where I bought the plans from and they say to just use dope or tape which I have tried. I also don't like the idea of having to reapply the dope or the tape everytime I want to fill it. Leaving it leak was also brought up, my compressor would have no problem keeping up with the leak but I just don't like doing things halfassed.

So I need some ideas for an air tight easily removed cover for a hole used to fill my tank with abrasives. The hole can be any size over 2" but I would really like a 6" round hole. The only way I see of doing this is to lay out my holes on the tank and the removable plate, weld nuts to the inside of the tank and then weld up some horizontal pieces for the studs to form a "T" and use a gasket.

The only way I can figure out how to weld the nuts on the inside is to cut an 8" circle out of the tank, then cut my 6" from that, weld my nuts then weld the 8" piece back in.
 
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riley.m

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Dec 10, 2008
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348
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Port Townsend Wa.
i wonder if you tried using something that wasnt galvanized.and also make sure you use national pipe thread or NPT it tapers slightly so it makes a better seal as you tighten the plug,also try using the blue colored dope and make sure it dries a little before you add pressure,i dont think that really matters but any little thing helps.hope this is relevant to your problem.
 

garfunkle24

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Mar 18, 2008
Messages
3,429
Location
Saskatoon, Canada
I'm building a pressure assisted blaster. For my abrasives fill hole I tried using a 2" galvanized pipe coupling as the bung. I welded the bung to the top of my tank, no matter what I try I get air leaks. At first I thought I warped the first one, so I made sure the second was welded slowly and kept cool. That one still leaked. then I tried a 2" -1 1/2 reducer as a bung, still have the same problems. Lastly I tried a ****** as the bung and use a female cap, once again, it still ^&*(*&%$ leaks. I tried pipe dope and teflon tape, still leaks.

WTF am I doing wrong? It's driving me crazy because I have ZERO leaks in my air lines, my air system has held air for over a week without kicking on. I only need this thing to hold 7-10 PSI's.

I asked on the message board where I bought the plans from and they say to just use dope or tape which I have tried. I also don't like the idea of having to reapply the dope or the tape everytime I want to fill it. Leaving it leak was also brought up, my compressor would have no problem keeping up with the leak but I just don't like doing things halfassed.

So I need some ideas for an air tight easily removed cover for a hole used to fill my tank with abrasives. The hole can be any size over 2" but I would really like a 6" round hole. The only way I see of doing this is to lay out my holes on the tank and the removable plate, weld nuts to the inside of the tank and then weld up some horizontal pieces for the studs to form a "T" and use a gasket.

The only way I can figure out how to weld the nuts on the inside is to cut an 8" circle out of the tank, then cut my 6" from that, weld my nuts then weld the 8" piece back in.

A buddy of mine used the neck and cap of the biggest radiator he could find in the junkyard. Ended up finding one from an pld White tractor. It's about 3" across I think. Also, as posted above, galvanised steel does not weld too nicely at all. It really shouldn't be that hard to find a leak proof filler/cap system. Good luck with your quest!
 
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LoneGunman

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Mar 27, 2007
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2,081
Location
The Gunshine state
A buddy of mine used the neck and cap of the biggest radiator he could find in the junkyard. Ended up finding one from an pld White tractor. It's about 3" across I think. Also, as posted above, galvanised steel does not weld too nicely at all. It really shouldn't be that hard to find a leak proof filler/cap system. Good luck with your quest!

Now that is an awesome idea, thank you very much.
 

mtwaterguy

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Joined
Nov 16, 2007
Messages
3,518
How about a cam-lock fitting. I use them on my water trucks to keep the water from leaking while the system is pressurized. I believe they come in 4" diameter and should handle your requirements just fine.
 

rsanter

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Dec 22, 2007
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18,524
Location
visalia ca
I used a pipe coupling on mine and the plug is a short piece of pipe with the end welded shut with a piece of metal and a T bar welded across that so it can be installed/removed by hand
I have had little to no leaks

bob
 

russlaferrera

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Nov 24, 2006
Messages
2,035
Location
Central Virginia
is your leak coming from the weld or the plug,i was thinking if the inside of your fitting was galvanized,it might be harder to seal.

If the weld is NOT leaking. Use a rubber stopper/plug (available at pool supply, or hardware store.) They come in sizes. Place the correct size in the filler tube and tighten the wing nut. As a safety, replace the pipe cap over the plug to ensure the plug doesn't fly out.
 
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nissan_crawler

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Jan 12, 2008
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Wichita, KS
You would still have to weld in a bung with female pipe thread. HOwever, that shouldn't be an issue. You could also get a pipe ******, cut it in half, weld that on, and then get a banjo coupling with female thread.

I think 99% of your problem is galvanized. I don't care how well you clean things up, it's a royal pain to try and get an airtight weld with it.

You can also buy weld in bungs. That's what I did for my air compressor tank.
 

mtwaterguy

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Nov 16, 2007
Messages
3,518
If you prefer ebay has screw on aluminum cam lock fittings. These are the type I use.
 
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LoneGunman

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Mar 27, 2007
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Location
The Gunshine state
I think I'd rather have the aluminum but won't I have problems because of the dissimilar metals being in contact with each other? I'd have to thread the AL fitting into a steel coupling or ******.

Nissan, the polyprop would be good for 7-10 PSI?

Bob, Are you happy with yours, works as good as everyone says?
 

Torque1st

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Joined
Sep 14, 2008
Messages
5,668
Location
KC Metro, Kansas
Thanks Nissan, those links will help with a future problem I have.

The best way to get rid of galvanizing is with Muriatic Acid. Grinding or sanding just seems to smear it out and mix it with the base metal.

Grinding on stainless steel always seems to mix whatever was on your grinding disk or whatever you were trying to remove with the base metal also.

I know how disgusting leaks can be...:lol_hitti
 

luckyhotrod16

New member
Joined
Sep 11, 2006
Messages
4
Try using a straight thread coupling and a straight thread plug with an O-ring. I've got a blaster with that and it works great. Another way that I have seen is to have a plate on the inside of the fill hole with a standoff and a t handle about 4-5 inches long with a rubber gasket on the plate. When you pressure up the blaster just pull up on the t handle and the air pressure inside the tank will push the plate up and seal with the gasket to the inside of the fill hole. It sounds a bit confusing but is pretty simple in practice. Let me know and I will try and find some pics.
 
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