Air Compressor Rust: Epic Fail

[@tench745]

I worked in a woodshop one summer, compressor ran all day, sucking in the humidity and dumping it in the tank. It was not uncommon to drain 1/2gal of water out at the end of a work day. Auto drains are a good idea.

[@gordbaker896]

Right. The bigger the Receiver the more water is collected.

[@paulmoffat9306]

I was at one industrial site, helping our area service tech, check out one of our compressors. They had a 2,000gal receiver tank, that was almost 2/3 full of water, whose auto drain valve was corroded shut, and the check valve on the compressor had also stuck in the open position. Hundreds of gallons of water and oil had back flowed through the compressor when they turned it off. A huge mess. Not under our warranty, but on the plant's service routines, as they did NO P.M.

[@mickwolf1077]

your compressor is a 50 year old hot water heater in disguise.

[@shanemedlin9400]

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.

[@sjb3460]

I always drain my air compressor after every use.

[@Peron1-MC]

it was nice of him to take it back. he clearly didnt know about the problem :/

[@AndySomogyi]

Hey, it’s pretty rare these days .

[@itsthemetho]

I purchased a used compressor for my father's place. I thought it was a great deal, but the 50L tank was seriously 1/3 full of water. I drained it, removed the crude from the "inspection port" and cleaned the inside up. Thankfully the corrosion wasn't as bad as expected, but what I didn't take into account was that the seller would ship it undrained and that rust particles had got into the pipework and valves. I spent about a year cleaning tiny particles of iron that would prevent the non-return valve from sealing. Finally I dissambled all the pipework and cleaned it individually. Finally it is a good compressor with a fantastic pump and electric motor. I'm not sure I would have purchased it knowing the amount of maintenance required to get it reliable.

[@thekingsilverado3266]

A good lesson is a compressor with a decent motor and do not discount the Chinese motors right now this new gen are decent. But if push comes to shove get yourself an expired mid sized COMMERCIAL GRADE propane tank. The box stores sell propane tanks and they are made of the same low grade steel. Get a tank from a propane vendor which is sometimes hard to do gotta talk to the right guy at them places. If you do not believe me there is up 3lbs in weight diff between them Chinese box store tanks and a real commercial grade tank.

[@vinceking7878]

Get rid, a rusty tank is a bomb!

[@scottmatthews172]

A lot of mechanics keep their air compressors outside the shop in a ventilated room made of concrete blocks.

[@AndySomogyi]

That would be perfect, it adds a lot of safety, and keeps the noise outside. Unfortunately, I don't have a place to put it outside. bummer.

[@scottmatthews172]

@@AndySomogyi Build one in a corner of your shop. Blocks and mortar for the floor to the ceiling add vents and a door and you're good 👍

[@AndySomogyi]

@@scottmatthews172 I've got literally inches to spare, with the tank pushed against the wall. What I will do when I get a new one is plumb the air intake through a hose into a air filter in the crawl space above the garage, that keeps a lot of the noise down. I'm also making an intercooler and water trap from an old AC condenser to go between pump and tank.

[@nelsondog100]

@@AndySomogyia video about your cooler would be interesting to watch. Show us how you do it😊

[@AndySomogyi]

@@nelsondog100 as soon as I get a new compressor and start painting , I’ll fab up an intercooler . It’s pretty simple, basically just mount the intercooler (automotive AC condenser ) on a wall so it has a little tilt so any condensation can drain . Then run the outlet of that into a water trap, then into the tank . I’m using a dodge ac condenser that has unusual lines, so I’ll just solder them to standard 1/2” aluminum tube and connect that to pipe fittings to go into tank.

[@ronblack7870]

i have had a 15 hp screw compressor with tank going back to the 60's . looked inside it had some rust but not crazy amounts. used it for 5 years till it was too small then traded it in . so tanks can last very long. there is one in my factory from 1943 . it's huge like 2000 gallons . we don't have it connected because it's in a closet behind a bunch of offices built around it . but i know it was being used till the mid 1980's . i looked inside by pulling the inspection hatch and it looked good inside. one thing is all my compressors have automatic or timed drains keeping the water out.

[@bobl1769]

Thanks for reminding me to drain and check my tank. You were lucky!

[@dadandkids5028]

Chinesium Oxide.

[@HDXFH]

NOT compliance tested, cheap shit

[@AndySomogyi]

@HDXFH it was actually pressure tested , has the welded on certificate plate . But my guess is when they pressure tested it, they didn’t drain it properly, and was never drained subsequently.

[@elektro3000]

I don't drain my 29 gallon air tank every time I use it, but I do open the drain valve until water stops coming out. Once it's just dry air, I close it and leave the rest of the pressure for next time. One of these days, I'll pull the valve and borescope it. Best way to check a compressor tank (for purchase or just safety checking your own tank) is to fill it up with water and then pressurize it with a pressure washer. Air is very compressible so if it explodes full of air, it's like a spring letting go and throws metal all over the place at high speed. Water isn't very compressible so if the tank ruptures, the water pressure drops to almost nothing and it doesn't throw shrapnel.

[@BryanTorok]

I was recently researching buy a small air compressor and read the manual that came with it and found it said that the tank was only rated for 2 years (might have been 3 years). I was astounded. This was one of the well known brands, but of course made in Asia, sold by Home Depot or Lowes.

[@AndySomogyi]

Wow, I know the 60 gallon tanks are rated for 10 years . Two years is crazy .

[@nyccollin]

It’s always been “THE Home Depot” and “Lowe’s” now. Mandela Effect.

[@ItchyKneeSon]

@@nyccollin The 'The Home Depot' app title text on my Android phone says "Home Depot". I taught English abroad for a while and am especially sensitive to common grammatical errors and and misspellings back in themfkn US. I have the same urge to constantly correct. But, sadly, language is 'living', 'moving', and changing constantly and most efforts to 'correct' are futile. In this case, you've leaned heavily into your 'tism. Mind you, there are many out there with an even more profound, deeper understanding of English than you and/or me. Have you come across any of THEIR corrections and applied them in your regular use of the language? If not, why do you think that is the case?

[@nyccollin]

@@ItchyKneeSon Either you experience the Mandela Effect, or you don’t. Research it sometime when you’re bored. Happen to remember the spokesperson for Publisher’s Clearing House?

[@MikeStavola]

I ran into something similar. Brand new looking 90 gallon compressor with a high end pump, which looked almost brand new. But... it weighed a TON. And it was full of sludge and water. And when we tried rinsing it out, we saw wet spots around the bottom of the tank, which meant it was leaking. It was run for a few months in a damp basement before the owner realized it was constantly running. Same situation with an old boss. He picked up a brand new pancake compressor, used it on two jobs (it was very rainy the whole time) and next thing you know, it had water sloshing around in it. I would guess that the compressor ran for less than 4 hours in total.

[@upsidedowndog1256]

I wish they lined the tanks better. My 22 year old compressor tank just sprung a leak. Looks almost new, works fantastic, but it is out of service until I locate a tank.

[@Itisinthehand]

Thanks chap, I’ll be checking the compressor I recently inherited.

[@sparkyprojects]

Warm air has moisture in it, that moisture drops out in compressors, mostly when pressure is released, you need to drain regularly, my guess is that the guy used it occasionally, released the air, but because he didn't use it again, there was no pressure to help drain it, ideally you open the drain when you finish using it to let all the air out. Check out the 'cloud in a bottle' experiment

[@Look_What_You_Did]

All air has water...

[@HarmonRAB-hp4nk]

air period, has moisture in it, when you compress a cloud persay its water :-\

[@aspensulphate]

Unless that air is cooled below the dewpoint, and passed through a separator before going into the receiver.

[@thomasswearingen6971]

One thing to note. In a home shop. When you are done with the compressor you should just open the drain and let it stay open. This will allow the tank to dry. When you keep air in the tank it is always wet. Most manufacturers say to store the compressor with the tank open.

[@cliffweinan3907]

Great story and advice on a "lightly used compressor". It's inside that counts and wise that you checked. These are time bombs because there is no way to know if previous user drained tank after every use. Stay away from used compressors and drain your new compressor daily.

[@rodneymiller5926]

Time bombs, lol. Stop spreading myths. Worse case scenario you get pinhole leaks where the tank rusted through. THEY ALL RUST ON THE INSIDE BEGINS ON DAY 1.

[@kurtzimmerman1637]

I bought a new craftsman 1 hp 12 gallon air compressor new in 1980. still have it 44 years later, and it works great!

[@Network126]

💣

[@kurtzimmerman1637]

@Network126 not a chance in hell! drained it every time I used it. thanks for being a moron

[@kurtzimmerman1637]

you're showing your stupidity! American made equipment doesn't fail. only Chinese crap you buy is unsafe! let's see how long your garbage lasts!

[@moi01887]

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.

[@igbeserk]

Glad you were able to return it. I snagged a Dewalt air compressor off Craigslist, it looked new. Home depot I believe had it for 400 but they were selling it for 150. the person indicated they barely used it. A week prior they stated they filled the tank with air and left it for a week and it still held pressure. I said noooo you're not supposed to do that. Brought it home, and emptied, refilled, and emptied a few times, brownish water came out from the moisture but eventually no more. Only used it a few times has worked well. I shouldve used my scope to check inside maybe i'll do that when it gets warm. Thanks!

[@cliveadams7629]

I'd accept the return if he was carrying that wrench when he asked for his money back.

[@AndySomogyi]

Ha ha, seller was super cool, didn’t to persuade with wrench . The drain plug hex size was 2 9/16”, but the wrench only opened to 2.5”, so I had to modify it by cutting an extra groove to open to 2 9/16.

[@AndySomogyi]

150 is a great deal . The tank walls are really thin on these, only 1/8”, so I think good idea to check.

[@igbeserk]

@@AndySomogyi thanks i will definitely. i think i've had it since october 2023.

[@bobroberts2371]

said " A week prior they stated they filled the tank with air and left it for a week and it still held pressure. I said noooo you're not supposed to do that. " Completely untrue, there is absolutely no reason a tank can't be left at pressure for extended periods of time. The " drain daily " is for draining water not bringing the tank to zero PSI.

[@VB-bk1lh]

I have five air compressors of various sizes. In the garage I've got one made in 1959, along side it is one made in 1933. At home I've got two portables, one from 1977 from Central Tractor, made in the USA, that one has had several leaks patched over the years. Its been springing leaks every 5 or so years and has been a problem since it was about 5 years old or so. It lives in the shed outback and only gets used to pump up tires and such. I bought a HF upright 30gallon compressor a few years ago on clearance and that lives in the basement to power my air nailers and various air tools. Its always on, and get drained weekly. The tank on that is thin, thin enough that the wheel brackets flex the tank under its own weight, but it was cheap, $40 on clearance missing a few parts. I've had it now for 9 years or so. It sits in a framed cubby hole in the basement, if it ever blows up, it'll likely be well contained. One of these days I figure the one out in the shed will need a new bottom welded into the tank, but for now, I just keep fixing the holes as they open up. I cut in about a 6" square section on that tank about 20 years ago. Its the lowest point of the tank where it had rusted pretty bad. The new piece is thicker and larger than the hole it fills.

[@AndySomogyi]

I’d be very careful with that, as I’ve read reports of compressors igniting the oil inside . Consider that’s under about 10 atmospheres of pressure, that’s a lot of oxygen bumping into those hydrocarbons .

[@VB-bk1lh]

@@AndySomogyiI think the chance of ignition of any oil in the tank would be rather minimal. Its under pressure but not compressed. It would also likely need heat to start the reaction. Its also air not pure oxygen. Years ago, around the time I got my current compressor, I had an old Gilbarco brand compressor that came from a defunct service station. It had a huge 3hp Westinghouse motor on it and a double V twin pump. It would top out around 277 psi on the high side and the 120 gallon tank was rated to 425 psi. It had a rattle in it as long as I had it, the shop scrapped it because of the noise. I ran it for a couple years, knowing it had a a rod knock. I backed down the pressure to about 165 or so and only ran it when I needed it. I seriously thought about fixing it but when I stumbled on a newer Quincy with a 10hp motor and double pumps I put the old one out to pasture. It sat behind the garage for a few years when we decided to see what would happen if we let it run unregulated. Half the guys said the tank would blow, the other have said the rod would let loose before that ever happened. At somewhere just over 320 psi, with no pressure control, the motor just couldn't turn the pump any further and it just stalled and sat there. After letting it sit for a few hours the pressure eventually leaked down back through the powerhead and we tore it down for scrap. The pump was too far gone to save, it was old enough to be a poured babbit rod and bearings so it got tossed, I kept the tank, knowing it was well proven and its not added air storage space behind my garage, its been there for 30 or so years now. (If it blows, all it'll damage is maybe the lean-too that covers it and some junk back there). The Quincy is a 1968 model, which was rebuilt in 1997. I figure its the last larger compressor I'll ever buy.

[@mythril4]

Don't weld it, get rid of the tank. You will eventually loose life or limb to that tank, air ruptures are VERY violent and are more common with old air compressors than people realize. If you weld the tank you'll change the structure of the metal and the points of weakness increasing your risk of rupture. I know you've been rather lucky, most people have not, be very careful with old tanks.

[@azmrblack]

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 😉

[@mikesbarn1858]

At one point Fridgidaire was shipping units full of water after test runs at the factory. Key pieces were pre rusted for your benefit?

[@crazycoffee]

Im just happy before anyone got hurt this got figured out. Im assuming from the factory they hydrotested it with something that sludged it up and was left in. I like old and used tools. Especially in the modern market. I have a lot of hand me downs and access to my family tools due to medical circumstances at the moment. Im so happy no one got hurt from this that we know of. I thought your car was a Jag at first. Im subscribing I like weird cars lol. I mean my project baby is my Toronado

[@AndySomogyi]

Tornados are cool. I’m weird in that I like the last gen 1990s eldorado / tornado.

[@dkindig]

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.

[@AndySomogyi]

Yup, that’s exactly what I’m doing . I’m plumbing a dodge AC condenser to pump, and setting up a water trap after it , before tank

[@danielebrparish4271]

Every air compressor forms water in the air tank. Compressing air heats it which allows it to hold more water. When the compressed air expands rapidly when it enters the tank which causes the air to cool. When the air cools it can't retain the water and it falls out like rain. Since water is heavier than air it falls to the bottom of the tank where it can be easily drained. All air tanks have a water drain valve. On trucks and busses the operator pulls on a cable that is connected to the drain valve at the end of every shift. This is especially important in the winter where the water can freeze and split the air lines which will prevent the brakes from being released. Trains and some trucks and busses have automatic water drain valves. You can hear them operate because it sounds like a ticking sound every 30 seconds or so. If you have an air compressor shut it off every day and open the drain valve until you hear air coming out of it. The water is mostly harmless but it does form rust which will shorten the life of the tank and is not good for the health of any air tools that are used with that air compressor.

[@steveashcraft718]

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

[@shawnbottom4769]

The electronic ones are usually adjustable.

[@jiminsequim3218]

I have my home compressor automatic drain set to come on for 3 seconds every 30 minutes. Works great

[@sjb3460]

I don't know where you live or where the seller lives, but in Alabama, we can have 90% humidity on a sunny day. That humidity is sucked into the air compressor tanks. At the machine shops where I worked, draining the airlines and the air compressors is a daily task.

[@AndySomogyi]

If the first owner had even drained it once , there wouldn’t have been any issues . I’m in Indiana , and running my existing compressor all day yields less than a cup of water . When I get a new one, it will have auto-drain and intercooler / water trap . I’m making an intercooler from a dodge AC condenser

[@TheKurtsPlaceChannel]

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

[@carlmaruyama6863]

My brother was a part owner in a GM/Cadillac auto repair shop. The shop would open and drain the compressor after each work day. The state would send an inspector w every few months and the inspector would use a magnet to check for corrosion. They passed each time

[@BILL-sb5kk]

WHEN THE BOTTOM OF THE AIR TANK BLOWS OUT IT IS LIKE A HAND GRENADE EXPLODING IN YOUR SHOP ! SMART MOVE TAKONG IT BACK TO THE SELLER. LET'S HOPE HE JUNKS IT AND NOT TRY TO SELL IT REAL CHEAP.

[@AndySomogyi]

Indeed, there’s an incredible amount of energy in a tank, I’d have to work out the math, but I think more than a hand grenade . He said he was going to take it back to Tractor Supply. My guess as to what happened happened is the factory hydro tests the tanks , I think they didn’t drain it properly. Then the first owner never drained it .

[@bobroberts2371]

Actually, the tank will start to leak from pinholes long before the tank rips apart. With larger tanks ( Over 3 gallon I think ) , there will be a ASME cert tag showing shell and end cap thicknesses as well as working pressure.

[@alantrimble2881]

WHY ARE YOU YELLING AT US?

[@BILL-sb5kk]

KEYBOARD STUCK ON CAPS. WAITING FOR AMAZON REPLACEMENT. SORRY FOR THE YELLING.@@alantrimble2881

[@oo0Spyder0oo]

A tank will rupture, it doesn’t blow like a grenade as the myths will have you believe. All tanks rust as moisture is drawn in with every tank fill, that’s why you need water traps for spray painting etc.

[@euclon]

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...

[@BryanTorok]

There is a material made for coating the inside of fuel tanks to prevent rust. I wonder if would work to clean and coat the inside of the tank when it is new to prevent rust from ever getting started?

[@AndySomogyi]

You’d think something as simple as a good epoxy paint would help immensely. I don’t know why they don’t paint them .

[@BryanTorok]

@@AndySomogyi Well. cost. They want to build everything as cheaply as possible and get you to come back a buy another in a few years. That, I would think they would need a coating that could tolerate expansion and contraction without flaking off.

[@Pje3ski]

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.

[@eudaenomic]

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.

[@paulmoffat9306]

One of my friends had an older Craftsman compressor, and I was horrified when he started it up and the TANK SIZZLED ! I immediately yanked the cord out of the wall socket, and told him just how incredibly DANGEROUS it was. A BOMB just waiting to go off. BTW, Sears Parts Direct, had a replacement tank available for not too much money.

[@AndySomogyi]

Wow, yeah, there's an incredible amount of energy in these, I just worked out the math and a 60 gal tank rupturing is almost the equivalent of two standard hand grenades. I did check with manufacturer and they wanted almost double for a replacement tank as a complete new compressor.

[@JohnMckeown-dl2cl]

I think I might be able to offer a possible explanation as to what may have happen and the blame would fall mostly on Dewalt. When these things are manufactured, part of the process is a hydrostatic test of the tank. The tank is filled with a dyed liquid (usually water) and then pressurized to the maximum and checked for leaks. In a "what if" scenario: suppose when the test was completed the water was not completely drained, maybe it was on it's side. The compressor tank plugs were installed and the mechanical parts were installed in the top. Compressors of this size are pretty heavy and the extra weight of a gallon or two of water probably would not be noticed. It sat in there for who noes how long after manufacture and then the year the original owner used it. This would be plenty of time for the corrosion you found to happen. The original owner, through ignorance or neglect, did a bad thing by not draining moisture from the tank daily as you are supposed to do, but by the time he got it it was probably too late anyway. If he had done things right he could have at least returned it after first use an gotten his money back for Dewalt's screw up.

[@AndySomogyi]

Yes, that’s literally exactly what I’m thinking happened now . I’ve been mulling this over for a week now , and no possible way just normal compressor use could have put that much water in the tank . The hydro test explanation is the only one that I think makes sense . The factory probably didn’t drain it all the way, maybe something debris clogged the drain valve ???

[@vc9743]

I worked at GSW for a while where they manufactured water heater tanks, they tested them using air pressure, they called it the "boom room" most odd. Why they would use air, I have no idea. Maybe just faster, less mess?

[@AndySomogyi]

@@vc9743 wow, that’s insane testing with air . Bet that must have been a very solid room. Where I work, they test small rocket motors inside inside a ridiculously heavy test chamber .

[@hjacobs8972]

My old compressor would usually have an ounce or two of water when I would drain it every week or so. However last year I didn't notice any water for several months. I became suspicious and put a wire into the hole. After some resistance I got a gush of rust and water, probably 12 ounces. I haven't used it since and plan to get rid of it. I was looking at Dewalt's compressors but now will avoid. Wish someone made 25+ gallon stainless steel tanks. I have so many cordless tools I may just close the book on large compressors. Don't paint or sandblast much anymore.@@AndySomogyi

[@AndySomogyi]

@@hjacobs8972 It’s weird that no one makes stainless compressors , stainless isn’t *that* much more expensive , and the cost of the steel itself is probably one of the lowest costs in manufacturing one of these . Especially with all the legal liability of exploding rusted tanks , you’d think they would make more in stainless . It turns out that most compressors, like dewalt, craftsman, Kobalt, etc. are all made by MAT holdings , and just rebranded . I am going to buy a new one myself , and I think I’ll just get a dewalt as I live less than a mile away from tractor supply . My existing craftsman makes about maybe , maybe 1/4 cup after using all day with air tools here in moist Indiana .

[@michaellowe3665]

They might fill them with water at the factory to pressure test them. Its much safer than using air. It may be that they didn't properly drain and dry it after the pressure test.

[@AndySomogyi]

Yes, that's exactly what I'm thinking happened. There's just no way that could have had that much water from normal use. My existing compressor makes maybe 1/2 cup after running hard all day here in Indiana. I don't know how much I drained but it was probably close to a gallon.

[@michaellowe3665]

@AndySomogyi same state. I have a very old compressor that scares me a little. I built a small room for it behind my garage to keep the noise down, and in case it dies catastrophically. I won't work right next to one after seeing some of those videos.

[@mortimergladbreath]

I bought my 80 gallon 170 PSI Husky compressor in 2005. I immediately installed an auto drain for it when I set it up. I have it on a timer so that it works from 10 pm to 6 am so as not to scare my wife when she walks by the outlet! Now I'm wondering about the condition inside the tank after all these years. I would hate for it to explode as it is sitting beside my 1992 Volvo 240 that is mint with 44K miles!

[@AndySomogyi]

I think with an auto drain , you’re good . Issue with mine was water sat in it for years

[@whip-its_dad4239]

Sorry that happened to you and glad you didn't get hurt .That's way too much contamination to be from just condensation , I'm thinking it could possibly have been in a flood ? Thank you for posting this .

[@AndySomogyi]

Thanks, it all ended up working out because the seller was super cool about it. I'm 99% sure the water is from factory where they tested the tank, but probably didn't drain it all the way.

[@DF-zp1os]

I replaced a 30 gallon that was 21 years old after pin hole leak on bottom. New compressor was a 60 gallon black diamond and upon inspection was alarmed at the start of some corrosion. With compressor unplugged. I mixed ATF with 90 weight axle lube and sprayed into the tank with a cheap paint sprayer. This created a thick fog in the tank and I let it settle overnight. Over the next year I drained pinkish water (ATF). I need to inspect the tank to see how this coating held up.

[@jimjones5644]

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

[@tZydeco]

Here's an idea. If the tank is in good shape rinse and drip dry a few times. Then fill with sugar cane molasses & water mixture. Let sit a few weeks then drain and rinse well.

[@AndySomogyi]

Problem was tank was rotted out, entire bottom corroded and steel was gone . Molasses kind of works because it has a small amount of phosphoric acid (from sugar processing ). It’s so much cheaper , simpler and easier to use straight phosphoric acid . Anyways , I took the compressor back to the seller and I’m buying a new one.

[@tZydeco]

@@AndySomogyi - I was more thinking in a generic sense, not your cases. In your case there was imminent danger.

[@budwhite3570]

I used to feel safe with my sanborn from 1992, and always drained it, tried to take care of it, still works,...but, makes me wonder. I bought a used upright campbell hausfeld that had more hp and larger tank, and the drain cock was open for draining, but it had been in a wet environment shed and got rusty on the outside and such, was supposedly hardly used,...but,...well, I'd like to have a real nice brand new compreessor that is for sure to be safe.

[@budwhite3570]

In gonna retire the used air compressor I traded for, the campbell hausfeld, ...might inspect the inside for kicks, I mean, it made me nervous the other day using a air nailer for a home project,...aint worth the risk....then there is my favorite, my old sanborn,...its not upright like the other, and I always drained it, etc, its a working air compressor, but I was talking to the woman of the house bout retiring it too, and I don't mean donating to goodwill or such, I mean, paying for disposal. It pains me bout my sanborn,,.....made in the USA early nineties, etc, and not really used that much really, its like an old air compressor aint trustworthy.

[@jan_vyhnak]

I would think about buying brand new tank and getting discount from the previous owner. I like to save things. I agree on hydrotesting because after first run of my new compressor I got little rust in the clean water coming out like they didn't dry it properly after testing. But it only on the first run. Now its clean. I believe it was surface rust from the factory. Maybe would be good spray inside with oil and get good separator to compensate it.

[@AndySomogyi]

You can’t spray oil inside , I’ve read about how compressors can explode from oil. It’s a high oxygen environment inside and any hydrocarbons could potentially ignite . I believe that’s why the manufacturer all specify synthetic oil - it’s less combustible. I did end up taking the compressor back to the seller and got my money back. He said he was going to fight with the store where he bought it .

[@jan_vyhnak]

@@AndySomogyi Makes sense. Maybe not that good idea after all :)

[@ct71rr20]

I have a Speedaire auto-drain on my 5gal IR. I have it set to purge about every 10 minutes for about 10 seconds when I'm running it. I've had my compressor for over 15 years.

[@shawnbottom4769]

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.

[@hydrocarbon82]

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.

[@ddellwo]

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

[@mythril4]

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.

[@1957mrbill]

I would highly recommend you install an air compressor auto drain on any non portable compressor. I have a float style auto drain on my upright, it has a clear bowl with a float inside. Condensate fills up the bowl, and once it gets high enough the float opens up the drain and then closes when empty. The other style I see on the market is an electric auto drain which drains based on an adjustable timer.

[@blkcoupequattro]

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.

[@mikefennema5561]

Hard to believe that much rust forms in one year.

[@eldoradoboy]

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...

[@Satchmoeddie]

It is an 1800! Good little cars! You need to crack the drain valve and leave it OPEN on an idle compressor.

[@AndySomogyi]

Thanks, I’m doing a lot of rust repair on the 1800, built a spicy injected motor ready to go in soon as I finish paint . Yes, sadly original compressor owner didn’t know you had to drain them :)

[@nelsondog100]

Is there nothing we can pour into the tank to seal it? I bought a compressor last year and only used it twice so far I’m curious if something can be done before I use it any further. I’m thinking there should be some kind of product on the market that would coat the interior and protected from rust…

[@AndySomogyi]

Oils inside the tank are probably dangerous as they can ignite (lots of pressure / oxygen). When I get a new compressor, I’ll make a zinc plug for the bottom. This will act like a sacrificial anode, as zinc has a lower electrochemical potential than iron, so the zinc will corrode and protect the tank .

[@nelsondog100]

@@AndySomogyi that’s an interesting thought I’ll have to investigate. Thanks for the idea.

[@azmrblack]

@@AndySomogyi Can you make a video about this? I'm sure a lot of us would be interested.

[@AndySomogyi]

@@azmrblack well, it would take a fair bit of work to set up an experiment demonstrating it, and I’m really trying to get all the restoration work done on my car . I can maybe do a quick talk video on the subject , and go over a bit of math showing the upper and lower bounds of combustion . Basically the pressure rise alone from compression isn’t enough to ignite (like a diesel), however if there is a spark or heat source , like say a failing pump bearing , and combined with a oily mist from a high volatility oil, and under pressure , it could lead to ignition . Much like a gasoline engine with a spark plug or glow plug. The conditions for this to happen are probably fairly narrow, but not zero. So I’d play safe and not use something like gasoline or acetone to clean tanks and use recommended synthetic pump oil.

[@azmrblack]

@@AndySomogyi I was referring to the Zinc plug for the tank you mentioned acting as a sacrificial anode and how you make it, but I really liked the explanation of combustion - interesting read 🙂

[@brianmeek5236]

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

[@brianredmond4919]

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

[@stevejones9062]

sounds like the tank maker had a tank left part finished in the back of the stores for years, it should have a spec plate with date of manufacture in any case, it was then used to complete an order.

[@bubbapate5740]

Getting water in your air tank is a natural by product of it pumping air. The air comes out of the compressor hot and goes into the tank, as the tank cools off the water vsapor condenses in the tank and accumulates in the bottom of the tank. All you need to do is put a better drain valve and tube on the bottom of the tank so you can reach it and weekly just blow the water out of the tank. Only takes a second. You can also get a kit that will do that for you.

[@jonbutzfiscina1307]

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

[@AndySomogyi]

Thanks, but this is all the 1800 I can handle :) If I had more room, I’d so love to have a Saab 96 though .

[@jonbutzfiscina1307]

I'm sorry, but I don't have a Saab 96. I have the 1800ES, 61 MGA, 1975 Bricklin, 1969 Volvo 164, and other various cars. It's time to let them go.

[@AndySomogyi]

@@jonbutzfiscina1307 nice, those are all great cars . Sadly I only have 1/2 of a two car garage . If I had more room, I’d also have a Saab 96, triumph TR7, Karman Ghia , Chevy Corvair, Datsun 240z and BMW 2002.

[@jonbutzfiscina1307]

How about a TVR? Engine frozen, but good overall shape. Unfortunately, there is no title. Not mine. Belongs to a friend.

[@AndySomogyi]

@@jonbutzfiscina1307 TVR, wow, super rare in US. As much as I’d like a TVR, I really need to focus on getting my 1800 all painted and driving

[@wolmntn]

That’s why I keep my compressor outside in its own shed. Not worth the risk inside my shop. Plus noise is way down

[@AndySomogyi]

Smart move . I’m pretty much stuck with it inside - no where to fit outside

[@ErtsenPlayGames]

i just bought tank used in industrial AC units as a liquid gas return tank on a scrapyard ( """ accumulator tank ,,, or ,,,, Liquid receiver tank"""" its same stuff like in standard AC /// heat pump mounted close to the compressor (that wertical "bottle" ) but with hundreds of times bigger capacity --- 100L or more most of the time --- its designed to hold returning gas in a liquid form It work at up to 20+ bar constant with changing pressure (designed to hold 28 or more bars //// around 406 PSI , tested most of the time to at least 30+bars Its pretty common to find because it need to be replaced after few years because of how high the pressure is inside at max that fluctuate all the time to just few bars if not used and temps also fluctuate all the time i clean it up pouring acetone inside and rotate , drain it , repeat untill clean + use rag for rest of the solvant (tanks like that have inspection / gas level float hole that u can almost fit your hand trough) --- when u get it its perfectly clean inside from any rust because its never in contact with moisture but can have some residual oils from AC compressor etc that u rly want to clean because they go acidic after contact with water (tank is 100% clean not galvanized etc steel) then when dried i poured 1 1/2 small cup (total) of paint for rims mixed with 1/3 of solvent for easier flow (for rims because one i have was pretty soft when fully dried, u dont want hard paint because it can crack overtime) and rotate , wait few min for paint to drip down then use some hair dryer from a distant (not to go "kaboom" but have flow of warm air inside for few min, then rotate it again , wait and again hair drier.... repeat until entirely covered inside (2-3 times) because first time 90% will drip down and leave for few hours with hair drier on low setting now u have perfectly protected tank from rust that will work for years and can hold way more pressure PS --- epoxy is also great idea and u can get stuff designed for that

[@jamiebennett6354]

All of my compressors have a drain valve on the bottom to get rid of any water the unit WILL collect through condensation or water in the air that gets trapped in the tank

[@AndySomogyi]

All compressors have a drain valve at bottom. I manually drain my existing compressor after each use, but that's annoying. First thing I'll do when I get a new compressor is auto-drain system.

[@ahorsenamedoaks1377]

The IR I bought new from TSC is the same way.

[@AndySomogyi]

Wow, that’s crazy, new compressor is rusted ?!?!

[@ahorsenamedoaks1377]

Yep

[@BIBIWCICC]

I had exactly the same with my dewalt. The inside had never been painted from new, dewalt do this because that know you probably only buy a compressor once in a lifetime, so they are designing them to fail. I stopped buying dewalt power tools years ago because of the quality issues, I should have stuck to my guns!

[@ptech88]

Im with you. I had all dewalt tools but the broke so often i threw them all away and switched to Milwaukee. Light years better

[@electrake2063]

I’ve got news for you, unless you buy a corrosion rated tank they are ALL LIKE THIS! When you push compresses moist air into a cylinder the air expands as it enters and the water turns into droplets inside the tank, that along with the warm environment and all that oxygen, and you get rusting. What you really want is a tank that has been treated to deal with water. Instead of putting that beautiful power coat finish on the outside, they should be putting it on the inside. This is why I gave up on compressors with tanks. I don’t like having huge bombs sitting next to me. Instead I bought a great compressor with a bad tank, removed the tank and replace it with a 2.5” capped 2’ long galvanized pipe / tank to thread the pressure switch into. I still have a drain, and then I put a fitting to connect the pipe to two separate 5gallon tanks I replace every five years. Costs less, and is MUCH safer to not have a fifty gallon time bomb that WILL kill you if it ever lets go near you and happens to want to occupy the same space as you while traveling through the side of your garage to your neighbors lawn.

[@emmettturner9452]

Would a misting of oil or Fluid Film inside the tank help?

[@AndySomogyi]

@emmettturner9452 I already took it back and buying a new one. Oils inside of a compressor are very dangerous because they can detonate. Inside a tank, it’s about 10 bar pressure, that’s a lot more oxygen in contact with flammable oils . There’s lots of reports of oils detonating inside a tank . That’s probably why manufacturers specify synthetic oils that can’t ignite as easily.

[@jfnotk255]

Humid air. A normal problem. Our bigger industrial devices have a automatic condensate drain function. Instead of the drain plug the have a valve frequently operated by the controller. But that is a quite different price region.

[@Truckguy2007]

I had a compressor that was 20 + years old. I just junked it and bought a new one.

[@rsnell22]

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.

[@Oneshot8242]

I may get a stainless steel tank at my scrapyard for a compressor setup. The compressor itself can be found cheap or free, because their tanks have rusted away, and it's cheaper just to buy an entire new unit. I guess manufacturing one out of stainless would screw up the planned obsolescence model that today's businesses depend on. Side note: I was given a relatively new, but cheap, compressor, which only needed a new regulator valve. Guess what? Nobody sells them, as they figure the valve and tank will fail, and that by replacing the valve, you'll extend the life into where the tank will begin to fail.

[@dayleedwards3521]

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

[@blipco5]

Take your bore scope and some wrenches when you go to buy it and check it in the parking lot.

[@ahmedkamalalkamali6929]

All tanks in all compressors weather it is old or new it has got one job , once the air being compressed in tank it makes the water accmulated down separately from the air.. It is the owner responsibility to do daily service by opening the drain plug every day if the water not drained these mud n rust oxidation will accumulate more n more resulting in property damage.. it is a must when newly buying it is necessary to dismantle n give a caught of an antirust agent inside the wall tank..

[@stevenewsam6698]

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.

[@DJ_Driven]

Would be nice if these air compressor companies would actually do a special coating on the inside of the tanks to prevent them from rusting and just charge some extra money I'd pay it. Otherwise it's instantly a problem from the day of manufacturer leaving the inside get all rusty and crusty.

[@ldnwholesale8552]

The water in the air is what rusts these things out. The standing on end tanks are worse than a laying down one. Every tank has a drain daily logo on them. Nobody ever does this ofcourse though I do drain mine semi regularly in the colder damper months. And use it most days. Clearly your seller never drained it. And while I think of it I will go drain mine now. Rusty red water will come out

[@corbman9049]

I got rid of our 15 gal Craftsman oil less compressor after when hearing hissing. Bought mid nineties it lasted to mid two thousands.

[@AndySomogyi]

That’s impressive for an oilless, they usually only last a year or so before the pump wears out

[@488ci]

Your supposed to drain them daily and high humidity areas draw in lots of water.

[@briana3467]

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.

[@mineown1861]

When buying a second hand compressor, factor in the price of a new pressure vessel . Warranty commonly is not transferable, only the original purchaser being eligible to make a claim .

[@phillipvansickle4220]

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.

[@MrRichard57000]

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

[@paulmiller6277]

I wonder doses tank supplier hydraulic test the tanks.

[@AndySomogyi]

Yes, a tank has to be hydro-tested to be certified. My guess is the factory might not have drained it completely. That's the only explanation I can come up with to explain the amount of water I found in it.

[@ruben_balea]

@@AndySomogyiDiagnosis: It was made on a Friday afternoon and/or by the new guy.

[@AndySomogyi]

@@ruben_balea Or possibly (probably) by someone who just didn't care, or wasn't paying attention.

[@ruben_balea]

@@AndySomogyi That's a joke we usually make in Spain when brand new things come wrongly assembled. But unfortunately some employees only try to do their job -properly- *good enough* when a supervisor is around to avoid being fired, but don't think about the consequences of their incompetence.

[@AndySomogyi]

@@ruben_balea indeed yes . It turns out that’s very true in many nations . In UK for example, British Leyland had a long history of quality control issues, and a lot of it had to do with which shifts spent a lot of time drinking at the local pubs .

[@petercampbell4220]

Air has a lot of water. If not drained even 1 hour of runtime is enough water, just need water and air is enough to ruin the tank. In fairness nobody reads the manual, that info is there.

[@richardsparks9904]

I would suspect salt water during shipping somehow.

[@HarmonRAB-hp4nk]

I can help, the person who owned it didnt depressurize it with the drain plug after each use thereful leaving the thing to rot inside...... we have a little air pig, took a bore scope down it, clean minus a couple spots... 10 years old not bad, If you take care of your stuff it lasts :-\ the previous owner obviously didn't

[@aspensulphate]

No need to depressurize. You're just needlessly fatigue cycling the tank, and putting extra wear on the pump. Just drain out the condensate after use, AND AFTER TANK HAS COOLED DOWN.

[@MB5150]

You were lucky to get your money back. There's many undecent people willing to refund you. Just chalk this up to experience. I've seen a few YT videos of "things to never buy used" mentioning air compressors being one of those. Good luck to you.

[@trunkmonkey355]

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

[@blainehouser4354]

Just WOW!

[@davekana8388]

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

[@oliverroedel1111]

I bought a used one, a traditional brazilian brand that made the stuff without any changes since the 50ties. the problem is the new stuff is trash. the old was made to last forever, the new to be cheap.

[@AndySomogyi]

Yes, I think you're correct. The tank material was a shockingly thin 2.4mm (0.095"). I had an older Sears compressor that was much thicker .

[@oliverroedel1111]

@@AndySomogyiexact, we needed 4 strong guys to carry the compressor, massive metal. and the type of steal was much better then the chinese bs. I drained the compressor today and the water was clear.

[@Sparky_GT]

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.

[@flinch622]

Rain? Seems unlikely. Maybe this was tied in as a backup on an old system - type 40 compressor or some such [remote setup] and old piping or original receiver not used for some time just puked its guts into this unit immediately the first time valves lined up from backflow. Oops. I like dessicant dryer towers to avoid air system dreck but... gotta change the beads out every year, or this kind of thing can happen again. Compressors can make a LOT of water most places: gallons a day anywhere near a marine or tropical environment with constant use - high pressure condenses vapor, and that's just how it goes. If that unit had a [mechanical] autodrain installed, the level of debris inside would at some point jam the drain port partially open. In a pinch... I go for a 1/4" ball balve adapted to 1/2" or larger piping or hose and crack it open just slightly during operation. Anyway, I am underwhelmed by dewalt over the years by a host of failures - I look at other things first.

[@dann8902]

It's from not draining the accumulated water after every use

[@THEjasonTDI]

That's what they all look like. They aren't painted. You drain them daily but you should get a decade or so out of a tank or moe depending on the quality. The sludge is compressor oil, rust and CONDENSATION from the air. You are pulling in air from the outside, compressing it and that heats it causing the moisture to drop out. Same thing with car engines. Especially turbocharged ones. (lots of water condensation issues in the intercoolers) You are really over playing the extremity of the situation.

[@AndySomogyi]

A quick calculation shows there's about 100 kJ of energy in a 60 gal compressor. That's the equivalent of almost two hand grenades. Now think about popping a balloon with that much energy, plus the shrapnel of the rupturing tank. So if you're fine with standing next to a pair of hand grenades going off in a closed area, go for it.

[@michaellowe3665]

When you heat air, it absorbs moisture. It doesn't drop out. Most of the moisture is dumped when the air escapes through the air tools. That's why they get cold and wet in your hand if you dont use an inlime drier. The only time moisture drops out in the tank is if it runs, gets hot, and then is allowed to cool down. This is a small amount, but adds up over numerous cycles. They couldn't use steel tanks at all if all of the moisture came out in the tank.

[@Look_What_You_Did]

@@michaellowe3665 Wrong.

[@michaellowe3665]

@Look_What_You_Did no, not wrong. Crack a science book. Warm air holds more moisture. Cool air holds less. The air coming out of the compressor is warm so it holds the moisture as long as it stays warm. It cools when it is released through the air tools and dumps the moisture. The water that gets in the tank is from the warm, moist air cooling slightly when it hits the tank walls. The hotter the tank gets, the less this happens.

[@bobuilt10]

​@@michaellowe3665 The air in the tank is warmer than the air outside of the tank, therfore the moisture will condense on the walls and run to the bottom. The compression is roughly 10:1 therefore each cubic foot of compressed air holds the equivalent of 10 cubic feet at normal atmosphere. Water in compressors is a thing alway has been and always will be unless you freeze the air before you compress it.

[@colescrustycars]

They all look like that. Its bare metal inside. The compressor would of failed long before that tank would. I'd buy that thing with absolutely no hesitation. The ones you see fail are from faulty safety valves etc.

[@zackjay71]

Drain your tanks from the bottom. Let the compressor run a few minutes with drain (valve) open.

[@catfish24]

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.

[@AndySomogyi]

Not a bad idea, however one of the issues with aluminum is it has a finite number of strain cycles , then will loose strength and fail. Steel however has an unlimited number of cycles . That’s why airframes are rated for a certain number of hours .