Compressors - drain every day or leave pressured?

[J. Clarke]

Thank you, sir. Made it up on the spot.

[krw]

What's wrong with copper? Copper tubing is still pretty cheap. The fittings are at least as expensive as the tubing for an extensive system.

[Ed Pawlowski]

Copper is a very common air line material. Easy to break into if you want to add branches later too.

[Mike]

No one is 'living in unreasoned terror of their tools' A statutory internal inspection of a pressure vessel might *never* find anything, but the defined periods and limits of that inspection are based on many years of practical experience, and nothing in that knowledge base can currently justify extending that inspection period by a few months let alone a few decades. It's absolutely bugger all to do with overpressure and regardless of the normal operating pressure the regime of inspection is identical.

A typical 100psi portable compressor typically used in close proximity to the work with portable tools might be viewed as more dangerous in failure than a 3000psi compressor used in air blast HV switchgear as for most of the time no one is anywhere near them when they are operating and they use chain mail screens to limit damage to the building and adjacent equipment.

Anyone operating a pressure vessel for 40 years with no internal inspection IS living on borrowed time, that's not just my opinion but that of thousands of professional pressure vessel inspectors, insurance companies and health and safety legislators worldwide.

[Leon]

But is it really still cheap? Residential A/C compressor condensing units are being stolen for the copper.

[Lew Hodgett]

Think your database needs an update on copper prices.

Lew

[Drew Lawson]

Um, no. There isn't much air in water, but there is a hell of a lot of oxygen. Water contributes to rust so well because water is self-ionizing (something to do with the shape of the molecule). A small fraction of the water is always free oxygen and free hydrogen.

Beyond that, I'm completely ignorant about the details of the steel that is used for these tanks. Maybe the typical tank-steel rusts very slowly.

[Jack Stein]

So, I'm NOT alone....although you got me by maybe 5 years. I had thought the tanks were lined in glass, someone told me that once... Now, I'm thinking metal rusts slower under water than just being damp? If damp metal is in contact with air, it rusts quickly. Not much air in water, so, leaving it in might be better than draining it every day?

Just wondering why my 30 gallon tank hasn't collapsed in a pile of rubble?

[Nova]

The price of copper has come down quite a bit over the last couple of months:

1/2" x 10' Type M copper pipe - $6.76 1/2" x 10' Type L copper pipe - $9.68

A few months ago I paid $68.00 for a 250' roll of 14/2 Romex. Last week it was down to $23.00.

[Jack Stein]

Good point.

Thanks for the link, but I got to tell you, it was way over my head.:-) I couldn't figure out if it addressed say a nail submerged in water vs a nail kept constantly wet/damp but not submerged. I'm thinking that a compressor is always wet on the bottom whether or not you drain it. What do you think? I don't have a clue myself, but I know I rarely have drained mine in over 30 years, and it still has no leaks, and the last time I drained it, about 6 months ago after a similar discussion here (where I learned the tank doesn't have a glass liner) I drained several pints of water into a glass container, no sign of rust, and no sign of oil.

I'm also thinking when/if it rusts through, it will go pfsssssh instead of boooom.:-)

Maybe they use, or used to use, or some use, a rust resistant, high nickel or something type of metal. I know mine is over 30 years old, bought it used, and my brothers he bought used when I was 12 years old, really old then (50 years ago), and it still holds air fine, no signs of leakage (he drains his though) I remember painting cars with it and it sounded like it was going to knock itself apart. My brother said if breaks, he'll buy a nice 2-3 stage compressor... still running still a knocking. I painted lots of cars and trucks with that thing, and it proves if you want something to break, it never will.

[Tom Veatch]

I'm thinking you're right. And the reason I think so is that the relative humidity (RH) inside a tank charged to 135 PSIG (factory shutoff setting on my compressor) will be about 10 times greater than the ambient RH. So anytime the compressor runs when the RH is somewhere above 10% you're going to get condensation inside the tank by the time the 135 PSIG (~150PSIA) shutoff pressure is reached.

If the shutoff pressure is below 135 PSIG, then the ambient RH necessary to cause condensation inside the tank is correspondingly higher.

Tom Veatch Wichita, KS USA

An armed society is a polite society. Manners are good when one may have to back up his acts with his life. Robert A. Heinlein

[David G. Nagel]

developed a couple of holes. These were in the bottom and would vent air and water when in use. The pump eventually gave out so I replaced it with one from HF.

[Leon]

Is an iced tea glass only wet on the bottom? It condenses moisture on the outside of the glass every where the glass is cooler than the ambient temperature. The compressor tank works the same way. HOT compressed air goes into the tank and the moisture in the air condenses every where on the inside tank walls. Basically the moisture is all over the inside walls untill the droplets become large enough to run down to the bottom of the tank and collect.

I firmly believe that draining the tank helps to slow rusting but more importantly it maintains tank air capacity and helps to keep moisture out of the air hose. A tank that has a 20 gallon capacity and has 4 gallons of water in it will recycle 20% more often, or something like that.

I had an 80 gallon unit fail that way, it was a slow death. With relatively low pressure and the fact that there is/are weakest points in the tank pin holes developed and leak. As they rust they become bigger and leak more. I suppose if you ignore that situation the tank could eventually explode or blow a larger hole.

[krw]

Yep. I put >150ft in my previous house. I'd like to do similar here.

[krw]

Type-L was $8.80/10ft hunk on the way home. Quick disconnects are $3-$5 each and 1/2" copper to 1/4" pipe fittings are over $3! Yeah, it's still pretty cheap. ...and it's so easy to work with (damn I hate the PEX in my new house).

[krw]

Where? I'd pick op three or four at that price! It was $41 at lowes on the way home. I'll be finishing the (u)FROG over the next year or so and would buy ahead if it were down that far.

[Martin H. Eastburn]

Copper Oxide - the black power inside - must be filtered out or it will clog any tool.

Having a quality filter at each site to trap the fine dust might be expensive.

Dryer at the front helps any pipe system.

Mart>> fittings are at least as expensive as the tubing for an extensive >> system. >

[Nova]

It was the contractor price at one of out local building supply places, Lenco Lumber. I checked their web site this AM and their regular price without the contractor discount today is $34.29 for 250'.

[Mike]

Think away.

Maybe.

Would you go into a disco with an epileptic...when the epileptic had a loaded gun pointing at your head? It has similar risks to an uninspected uninsurable pressure vessel.

(answers such as I can't dance and I wouldn't go into a disco are not permitted)

:-)

[Leon]

Actually I think a closer comparison would be the epiletic hoalding a loaded gun to your head and an eliletic pointing a loaded gun at a pressurized container that you are setting on. As story hungry as the media is I don't recall having ever heard of an air compressor exploding and I have worked around compresssors for my entire professional career.