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Checking a compressor for safety

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Valiant

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Hey all,

Long time no visit! I've recently been offered a Machine Mart Air compressor, it's 10 years old, been used twice for charging some accumulators and then stored in the spare room by a mate of mine. Hasn't been bleed and unsure if it was stored charged or not. Visually it looks fine last time I saw it apart from one of the gauges being bashed about by really useful boxes.

How would I go about checking that it's safe and won't blow up in my face or something? :lol:
 

Vann

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I'm following with interest as I have an industrial compressor that's as old as Notre Dame (well, maybe not quite). I sometimes wonder about the tank and whether there's some way to test it...

Cheers, Vann.
 

dzj

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The thickness of DIY tanks isn't anything to speak of and who knows what has happened in the ten year period of dormancy.
An industrial tank, though, might be worth having hydrostatically tested by someone who is in this line of business.
Apart from the tank, there are other safety concerns also.

A new DIY unit isn't that expensive nowadays. :)
 

novocaine

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Diy or industrial makes no difference, they both have to meet the same standard and legislation. Unless you mean higher pressure from an industrial unit which will then have a thicker wall.

Pull the drain and stick an endoscope in. If it looks like there is a shed load of rust tgen get it hydro tested. If not then crack on unless you feel nervous then get it tested.
 

Trevanion

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Gosforth Handyman put out an interesting video recently on the same subject lately.

[youtube]akAoznYEzts[/youtube]


I've never seen one explode but I have seen pinhole air leaks in tanks before from heavy pitting inside the tank.
 

Fitzroy

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Interesting video. ASME VIII codes would result in tank wall thickness of c. 1mm for 8 barg (120psig) and 30cm diameter. At 2.4mm from the vid, max pressure allowed would be c. 17barg.

In my industry we don’t deem vessel rupture due to pitting corrosion mechanism as credible. It requires something that impacts large parts of the vessel ie over pressurisation, underchilling resulting in embrittlement, or a chemical degradation of the gross material, ie hydrogen embrittlement or hydrogen induced stress corrosion cracking. Pitting corrosion at design conditions results in localised leeks.

Ps disclaimer, not advocating you do or do not use, just providing some info of relevance.

Fitz.
 

dzj

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Fitzroy":2n3zmgtq said:
Interesting video. ASME VIII codes would result in tank wall thickness of c. 1mm for 8 barg (120psig) and 30cm diameter. At 2.4mm from the vid, max pressure allowed would be c. 17barg.

Fitz.
I remember reading product details of a 25l model.
It said wall thickness was 1.8mm.
I thought it was a typo. :)
 

whatknot

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Glad you posted this, its a subject I have been interested in, as I am after a 2nd hand compressor, I can't afford a new one, even if they aren't that expensive new

Oddly just saw one on a selling page, it looks like Noah had it on the Ark ;-)

Totally covered in rust all over, I wouldn't trust that at all
 

Lons

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I had an ancient SIP one that I was a little concerned about as it was rusty when given to me so I made a slatted crate from pallet wood and a drop on lid just in case. Used it regularly for 15 years until the motor died and I had to buy new. My reasoning was if the tank split then it would be contained.

I'm not advising anyone to do that as I have no idea really just saying what I did.
 

Inspector

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If you really want to you can do your own hydrostatic test by plugging/capping all holes in the tank, put a pressure gauge on it, fill it to the brim with water. Then you screw in a grease nipple and using a grease gun pump grease into the tank until you get to the test pressure. I believe that should be one and a half times maximum operating pressure but double check. Then you wait a few hours and see if any leaks show up where they don't belong. If it leaks from a weld et cetera then scrap the tank. If it doesn't you are good to go. Drain the water and grease. Dry it out and put the fittings back on.

It's a lot of work and I haven't done it to my 80 gallon, 30 plus year old tank but the water drains out clean and it gets light use. You decide whether it is worth the effort to test, get tested, buy new or live in ignorant bliss.

Pete
 

Pete Maddex

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If you think it is dangerous just get the wife to switch it on.

:D :shock: Was I :wink:

Pete
 

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