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There is more water in the air than you might think. Air is a mixture of gases, each at it's individual partial pressure. The sum of these partial pressures comes to whatever atmospheric pressure is, about 14.7 psia. Water vapor is the only component gas of air that can be liquified by a typical air compressor. In many areas where prevailing dewpoints are high, the partial pressure of water vapor in the atmosphere can reach 0.4 psia which corresponds to a dewpoint of about 74F. When you compress air from 14.7 psia (0 psig) to 140 psia (125 psig) you increase its absolute pressure by a factor of about 9.5 and decrease its volume by the same factor. This means you increase the water vapor pressure and decrease its volume by that same factor. In the case of 74F dewpoint air, that vapor pressure is increased to 3.8 psia; however it can't stay in gaseous form at that pressure in typical ambient garage conditions. When this air is stored in a tank that is kept at typical ambient temperature, that compressed water vapor is going to condense to liquid water inside the tank until the dewpoint inside the tank is equal to the ambient temperature of the tank. The only solution is to either dry the air with a desiccant or refrigerant air drier (an option too expensive for small shops and homes) or rust proof the tank or fabricate the tank out of some rust proof alloy. In order to prevent condensation inside a 125 psig tank, the intake air would need to have a dewpoint of 12F or less. If, for example, you initially fill a 25 gallon tank with 125 psig air that has an ambient dewpoint of 74F in a garage ambient temperature of say 80F, you are going to deposit almost all the moisture in that air into the tank, in liquid form, as you reduce the charge air volume from 32 cu ft to 3.3 cu ft; btw, this yields about 0.6 ounce of liquid water. It doesn't take many cycles to gather significant water in an air tank if it is not drained. It should also be noted, that inside a compressed air tank, without some sort of air drier, the relative humidity will always be 100%. The internal surfaces of the tank will always be damp. This is the case because the air inside the tank contains water in its gaseous phase in closed-system contact with its liquid phase. These internal conditions inside compressed air tanks without corrosion protection makes them all ticking time bombs. I personally wouldn't keep one more than 10 years or so...

Thanks for the new series to follow !!! It seems that although rusty it is, it's still strong Swedish quality work and good base to work with. Thanks and keep going! Cool looking 1800ES, very rare at least here in Finland.

The Hudson Hornet is a wonderful car. I'm glad Pixar made it famous to a whole new generation.

Sounds like Rolls Royce Merlin V12

What a piece of crap mill lol.

Hard to believe that much rust forms in one year.

Tim Dewayne Whaley

Andy: I know I’m late to this party… the ‘72 unit I have was leaking out of the little silver box on the back of the M41 that holds the reverse switch contact. Not much gasket there.

When air is compressed, excess water precipitates. If it is raining outside, the precipitation is more. In that tank, if the air pump was running regularly, it could buildup a half an inch weekly. I went to work some place in Augusta GA. Nice humid area. And the compressor was having problems. I wasn't the supervisor, but I checked the compressor and found the drain and opened it. I gave up counting after 4 gallons of water and oil muck. But I would venture to say that are 75 gal tank em was at least half full. It took about 40 minutes to drain the tank under full pressure.

I'm about to sell mine to a friend. I guess I'll be borescoping prior to the sale.

Hi Andy, this Is Alberto from ab-shop Italy! I saw your wonderful surface/ tool grinder and It Is what i'm searching around the Europe! ( Because It Is small for small workshop and perfect for a bench) Could you please write me the "brand" or the model that It Is wrote over there? I will search your machine hopefully to find one like that!! Thank you for your help in advance, a big Ciao from Italy, Alberto

I've got couple compressors, one is 25 gallon Sears, and the other is 20 gallon Sanborn, when ever I drain them they don't have a lot of water in them, perhaps the humidity locally were the it was use was relatively high, or someone has left their unit on and the unit runs frequently without them knowing it. I'd be suspect of Dewalt Compressors of a certain era after seeing this however.

Very interesting. Thanks for posting this. Have a nice day now.

This guy totally looks like a “Volvo Guy”………..😂

It's possible to safely test these tanks using a pressure washer...and obviously 60 or 80 gallons of water. If there's a leak or blow-out, the incompressability of water means the pressure drops immediately. You have more risk from the flood water knocking you over than shrapnel.

Don’t buy used air compressors! Not worth the risk

Don't leave the air in the tank unless you have some sort of dehumidifier that the air goes through before going into the tank. I just empty my air compressor after each time I use it.

My god wellcome to the real world. Akl compressors gave water in them because there is water in the air. Its calles humidity. This is why there is a drain plug at the bottom.

Sounds to me like factory sabotage. Like the half million dollar chiller which came with factory settings which would cause it to self destruct. It had also gone through a drive-by commissioning.

Looks like these companies that make compressors would make the tanks out of a good grade aluminum l know it would cost more but there's no price for safety.

You at an idiot, all compressors leave water in the tank. You have to drain them regularly!!!

My 60 gallon CH I bought at Home Depot 21 years ago seems to be fine. But I’m moving in 3 or 4 years and will probably let it go with the house. I want a smaller mobile air compressor. Battery tools have come a long way since I bought the one I have. And I also try to drain it after every use and leave the valve open and the tank unpressurized when not using it.

Maybe it came from florida

I’d like to check out you automatic air drain, interesting, liked and subscribed!👍

Tank made in china, avoid it

Think your tank is never drained...have to check mine tank as well...

Any air tank will rust over time, the manufacturer cannot realistically protect the inside once it has been welded shut.

if you live in a humid place it will be way worse, i drain mine every few weeks, but im in a real dry climate.

By now most people know that air compressors collect water because there is water in the atmosphere, the compressor collects the air, compresses it in the tank, and concentrates the water. The more humidity, the more water. Tanks can rupture, sometimes with catastrophic results. Drain your tank. Do it often.

Wonder if you could install a stainless sump tank at the lowest point in the tank to collect the water/gunge ?.

This has been a issue with every air compressor I have owned. I'm surprised that you pressured the original owner into refunding your money on a clearly used air compressor.

I would suspect salt water during shipping somehow.

I can give a some folks a clue that alotta products are being sabotaged at the moment. To have this occur it would take a lot less than just a beer can of salt water and a mild acetate and this would happen. I have heard of the Dewalts and the porter cable compressors in particular. Don't think this ain't a method to steer folks to places like Harbor Freight or online CHinese vendors. It is going on.

I think y'all found where the CIA hid Bidens brains....

The so called Drains are Couplings shoved through a hole and welded on the outside. Tank cannot drain completely. A Half Coupling should be welded Over not Through the hole. They are a bomb and collect a lot of water when in use. A Borescope does not tell you much. Ultrasonic Thickness testing is much better. New Tanks not available.

Just WOW!

I would guess that the guy used it hard for a few days, got done with whatever he was doing and never bothered to drain the tank. The belt and pulleys aren't going to tell you a whole lot. Do yourself a favor and order a nice compressor. Box stores rarely carry halfway decent compressors. 80 Gallon, 240V, 5 to 7.5 HP...it will run all the air tools your little heart desires.... and drain the friggin tank after using it. I put an extended drain on mine using soft copper tubing and a ball valve from the hardware store.

When I buy compressors I pay as lot of attention to the ASME pressure certification. MY current one is ASME certified to 480 PSI of working pressure, why does that matter? It tells you the thickness of the metal and the size of the weldments. I working certification of 150PSI usually indicates a very thin tanks which also means it has a short life, especially of the metals used are very low grade.

When you buy something new always look for a manufacturer date on it, many places don’t rotate the stock, especially on larger heavy items

I worked at a place that had automatic blow downs that routinely blew down the air compressors.And like the mosture is gone automatically.

One of the best ways to prevent this is to pipe straight out of the compressor motor to something like a minivan AC condenser with a repurposed gas cylinder as a water catch tank then route back to your main air storage tank. Bonus is you get nice dry air too.

First thing, when a single stage compressor is set to run well over 100 psi, the amount of moisture the air can "grab" is much higher due to how much it is heated. It is also extremely inefficient due to the air cooling off in the tank which is also how all the moisture drops out. If you need more air, get a bigger tank, a bigger pump, get a two stage pump, or all of the above. Single stage pumps should cut off at 100 psi or less. Second thing, manufacturers are just asking for people to not drain their tanks by placing the petcock in a hard to reach spot. Especially if it gets stuck and you need to use pliers on it. I plumbed mine out towards the side of the tank so it is easy. Edit: comments suggesting lined or stainless tanks are just a band-aid. The root cause is you need to keep your tanks drained! Bare steel is absolutely fine then. It seems there isn't good understanding of how relative humidity works. Compress air, it gets hot, can hold lots of moisture. Air enters tank, cools off, can't hold as much moisture anymore. It's that simple.

You made a smart and safe choice. Everything you said is correct - unless you bore scope them, you have no way of knowing their condition. It can look brand new on the outside but it has cancer (rust) on the inside. Glad the seller was a good guy and he refunded you as well - I would have done the same, but at the same time, I wouldn't sell a bomb to someone 😉

Need another 1800es project? I have my Mom's 73 for sale.

in humid conditions.. just one or 2 days of run time wire wheeling or grinding or such where the compressor runs continuously or nearly so will net you a bunch of water... and then since an air tank is well not air tight, or is pumped full of air.. letting it sit for a few months you will get exactly rhat that one had.. which si why big shops run air dryers.. and at home you should drain each day at the end of the day.. my vintage busses that restore and cruise around in.. will spit actual water each time the compressor shuts off.. if its humid out and I put my hand under the air dryer purge valve, a single cycle of the compressor to fill the tanks up will spray my hand till its pretty wet whe nthe dryer purges...

Don't buy used stuff... Drain your compressor regularly.

I crack my compressors drain everytime I walk by it. Automatic drains help but don't vent long enough to get the moisture out.

Always keep your compressor in a cage., they will explode. I plumbed mine to a carbon fiber CNG tank so I don't have to worry about rust.

Awesome! I have a 73 ES project that will need all this and more! Subscribed!

Wow that was nasty! I see a lot of exploded-compressor vids here on YT... I guess I'm the lucky one. Bought an old compressor from a friend, used it for a few years then we moved and it sat for about a year and a half. When I went to use it, I noticed a hissing noise coming from the bottom of the tank... there was about a 1.5" crack where it was leaking. Needless to say I released the pressure and it'll never be used again.