Compressor tank- How much rust is too much rust?

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Old 01-18-19, 03:32 PM
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Compressor tank- How much rust is too much rust?

Hello,
I recently acquired a 1994 vintage Speedaire 3/4HP compressor. It runs quietly & develops full pressure, but I'm a little concerned about the level of surface rust on the ASME rated tank. I plan to completely restore and repaint this compressor if the tank is deemed safe. I have two questions:
1- Should I be concerned about the level of rust for tank safety? It does seem solid as new, just looks bad.
2- What is that cylinder shaped device hanging on the output of the pump? Some sort of intercooler or a check valve?
Thanks,
Andy
 
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  #2  
Old 01-18-19, 03:40 PM
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Hard to tell from here but that rust doesn't appear too bad. I would sandblast the whole tank and do a quality repaint, the metal on the tank is fairly thick so surface rust shouldn't cause any weakness problems. The canister on the pump looks to be a muffler to keep the noise down.
 
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Old 01-18-19, 04:20 PM
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Muffler or cooler..... not the check valve. The check valve is the brass item screwed directly into the pressure switch stalk.

That tank looks good outside. It's actually rust from the inside out that does most of the damage. If you are concerned about internal rust..... take and tap a hammer all along the bottom of the tank. It looks like the tank is pitched down on the motor end. That's where the problem would be the worst.
 
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Old 01-18-19, 04:39 PM
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So its the internal rust that can be an issue, not external.

However, what is your max pressure on that compressor, 70psi?

That is a little tank, not a lot of volume so even though there is a chance it's got some rot it would most likely develop a leak vs exploding like the YouTube videos!!
 
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Old 01-18-19, 04:57 PM
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You can see the outside rust. After you sand or scrape it..... you can see the tank condition visually.
No way to see inside the tank. If it wasn't properly drained... water was in there for who knows how long.
 
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Old 01-19-19, 01:55 PM
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As you compress air, water is squeezed out...and it sets and degrades the tank inside where you can't see the damage. I would first look for a drain on the bottom of the tank...but probably not there...so I would remove the line/pipe to the tank and see if I can dump out any water...(after I drained the compressor oil) It isn't easy to see much, but I would still look inside with a light/mirror or send in a probe to see how much loose rust is in there. I would use an awl or other pointy thing to tap along the bottom and thru any external rust to see how pitted it is. It is still a judgement call but that helps to decide. While a leak may be more likely, unleashing that much compressed air all at once would be impressive.
Be sure to replace the compressor oil!
 
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Old 01-19-19, 06:27 PM
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Thanks guys. It does have a drain. When I got this compressor last Tuesday, the drain petcock handle was broken. I put about 20 pounds in the tank, then slowly removed the valve. You should have seen the oily water shoot out! I did the hammer thing all over the bottom of the tank, and it sounds and feels quite solid, so I think I got to it in time. There is a 2" bung on the end of the tank (ASME required) for inspection, but I've been unable to remove it, because it seems that it was tightened by a gorilla or something. Other than this, disassembly, cleaning, and replacing rusty hardware is coming along well.
 
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Old 01-20-19, 02:35 AM
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You should have seen the oily water shoot out
That indicates the tank wasn't drained regularly. Not much you can do about that but going forward if you drain the tank after each days use it will prevent the reoccurence and keep moisture from building up in the tank.
 
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Old 03-04-19, 07:17 AM
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Restored!

Here are two pictures of the restored compressor. I refinished the tank & motor, redid all the plumbing, new pressure switch with 4-way manifold, new hardware, new air filter, and new wiring. Originally, the pump & motor were mounted on the wrong side, covering a 1/4" tank port. I reversed everything to make the port accessible, and installed the switch & manifold there. It runs like a champ!
 
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Old 03-04-19, 09:39 AM
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almost looks brand new
 
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Old 03-04-19, 01:54 PM
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Wow..... nice job. Looks great.
 
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