Thread: spray gun and little black bitties

I use a long copper airline with a slight fall back to the tank ,a long t piece with a drain plug in the bottom .and a pressure regulator ,next to where the gun connects also has a drain plug . works well in high humidity . or get an in line carbon filter. cheers Bob

the tank was full of crap - i got one of the bungs off and squirted water through it untilit ran clear - the other end bung won't budge

also the line was full of black shyte so i replaced that plus new filter reg at the tank and a new filter at the gun - hopefully it will shoot clean in a test run this arvo

Good that you found your problem hope, all is good for you now.

I'm not sure what Soundman means by "traces", phosphoric acid neutralises rust, any of the rust will be made inert. As mentioned before you will still have bare metal which will again be affected by moisture once you pump air with humidity present in it back into the tank. If after water you flush with meto you will get the inside drier before you start the compressor up.

We have always insisted that guns be washed thoroughly, using solvent to dissolve the paint immediately upon completion of the job, Whether you use three bowls or one bowl three or more times all paint needs to be flushed away and obviously the only way is to completely dismantle the gun. You should keep in mind the paint only is present in the pot the feed tube and the material tip at the front of the gun.

The air cap should not get paint in it only air, though some paint may be present on the outside of the air cap depending on where and how the gun has been during use. never submerge the whole gun in solvent you only risk introducing the paint in the solvent into the rest of the gun where there is only air and you will wash away all the lubricant on seals and moving parts.

I've never heard of the "dreaded black spot disease" in neally 60 years of spray painting.
Its as you found muck in the air or paint or some other reason.

Unless you need to spray "hammer finish" which contains silicon you should not have silicon anywhere near where painting takes place. silicon of any type in paint from polishes or waxes etc is normally banned from being even near a spray situation due to its disasterous affect on the paint. A "one use" gun for such a material would be best as it would save lots of solvent needing to be used to return a gun to normal use after the silicon in the paint either by adding of drops or otherwise is washed away.

Bob, you should get a better result with your copper pipe if you run it up the wall to the highest point then make the horizontal line drop away from the tank towards the gun, you don't want the water getting back to the tank you need to keep it moving away so you can cool and collect it.

Take off horizontal pipe from the top and go back down with a "U" so the moisture in the line can't jump up off the bottom of the pipe and as you said on vertical pipe use a "T" to take the air sideways and get the moisture run to the end and bottom of the line where you can drain it off.

"Picker" let us know how you go now your clean!!!

I have many times used posophoric acid and the rust converters containing same.......the notion that any acid neutralises rust is nothing more than advertising hype.

any reaction between an acid and a metal is a corrosive process the products left behind will be some form of salt or related compound....in addition you will by using acid be changing the PH of the metal surface and there will be unreacted acid remaining.

I have made some tests and I conclude that steel treated with posophoric acid or rust converter is more prone to corrosion than untreated metal unless that metal is immediately sealed.

try this.....take two large clean steel screws......scrub them with thinner.......then wash one in posophoric acid and rinse with water....dry it with hot air......put both outside for a while........tell me which one rusts fastest.

there is no point getting the inside of the tank particularly dry... because next time you run the compressor it will be was wet as it was before you started.

if you do not wash the gun out with clean thinner after the first wash, there will be paint residue remaining from the dirty thinner...... and fess up... how many clean their guns properly immediately after each use.... seriously

Any spray gun that is heavily used will get paint inside the aircap and in the air journals in the aircap........scrubbed plenty of them to know.

most new sprayguns use teflon or similar seals in them so the paranoya about not dipping your guns is far less justified than when cork and leather were used.

well I have heard plenty of people complain that they have black specs in their clear or white finish.....and it is obvious when you look what it is it is specks of paint comming out of the gun....... due to poor cleaning.... or is it that I hang around with people that spray a lot of black

there are plenty of paint products that contain silicon, any of the high temperature paints are likley to contain silicon, likewise some of the wood treatment products used in marine.

The standard recomendation and standard practice in the industry is to slope the air line back toward the tank... the idea being there is going to be water in the tank anyway so any in the airline may as well drain back there to be bled off when the tank is drained.

upward or sideways takeoffs are very commonly recomended...... but if you make sure your air is dry before it gets into your piping, you do not need to worry......as I said since fitting a second reciever followed by my normal filter reg, I have not had a whiff of moisture in my pipes.......I have two mates who have done likewise and they have similar results.....all of us use high volume air tools and spray also.


it's all good

cheers

Soundman your opening statement that -
"The notion that any acid neutralises rust is nothing more than advertising hype"
show how little you actually know about the painting process.

Every new car and any steel product painted with the intention of gaining the best cleanest surface to paint over has been subjected to phoisphoric acid. All new cars are put throught a washing process where the entire body is submerged into a tank of phosphoric acid or is put through a spray wash of the same. If you googe phosphoric acid you will see its one of its main uses.

No paint company would honour a guarantee to reimberse for a faulty paint job if it was determined the painter had omitted first preparing the steel with phosphoric acid. All paint companies sell phosphoric acid metal conditioner and insist on it being used on steel before any primer.

Your test is faulty the surface you think is rust is not it is the protective phosphate coating in other words a poor test which is wrong.

Your thoughts on cleaning a gun are just logical, if it wasn't cleaned properly there would be paint left behind. So yes you obviously hang around with a lot of guys who use black and don't clean their guns properly. I work with teenagers who try not to clean the guns properly but as they can't hand it in to the store without showing it to a teacher while its disassembled they clean it properly the first time.

Yes there are lots of paints with silicon in them but you don't use them in the same spraying enviroment as those without.

Don't know where your standard practice directions come from but I just Googled Compressed air lines and this came up.


http://www.webbikeworld.com/t2/compressed-air/

note that in the automotive painting process, we are talking about reasonably clean material and... most importantly....the treated surface is sealed immediately after acid treatment.

and yes I am aware that most of the etching primers contain phosophoric acid......but in that case also the metal surface is sealed in the process.

the interior of the compressor tank is not and can not be sealed ( within reason) and any remaining corrosion promoting acids or salts will remain in the tank and will persist in the tank.

my test is not faulty and I can tell the difference between rust and phoshate.....do the test and leave it a while.

Lets face it... most amateurs and a large portion of low end professionals do not clean their guns properly.. for the entire life of the gun.

As for standard practice of drainage direction of air lines back to the compressor......most of the leaflets that come with spray guns will detail it this way, as do all the books I have read on the matter......likewise the recomendations people I know who do this stuff........and confirmed by systems I have seen installed.

also you have a small system with one or two main branches all up in the rafters you don't want to be climbing into the rafters evrey time you want to drain the system.

It is logical that you do not want water draining toward the air outlet, you are better off the water draining back into the reciever where it can be drained off with the water that will always accumulate there.

If you are talking about large systems with multiple drains with low and low points that is an entirely different thing.

what is important is that proper measures , whatever they are need to be made to drain the pipes......if not the water will eventualy come out of the outlets.

While we are on the subject of copper airlines......one needs to be very very carefull about the grade of copper used in air systems.....the use of standard anealed plumbing copper is very dangerous....... my mate barry who used to install compressed air for a living was called out to a large system installed by a competitor ( barry was far too dear) .....the copper line had failed and split down the seam....the broken ends had flailed about and shredded anything within reach......fortunatly no one was killed or badly injured, apart from a lot of ringing ears and dirty underwear the company and staff got off very lightly.
If you are going to run copper, you realy need to know what you are doing and and be absolutly fastideous about the materials and the workmanship.

sorry a motorbike magazine is not a great authority on compressed air.
show me an article on a major manufacturers site & I'll cop it sweet

cheers

Is anyone except soundman and myself are still looking at this thread as Old Pickers problem was solved ages ago?

Somehow its turned into a to and frow between the two of us.

I don't think Soundmans take on the the problem he see's with phosphoric acid on steel is of any substance but he obviously thinks it is. I have never in 40 odd years seen or heard of PA being the problem he thinks exists.

My original knowledge about the piping of compressed air was as a student and then given to me to teach students in painting at TAFE. All theory was sourced from those who were responsible for the products. Paint from the manufacturers who needed information they wanted followed so their products would perform properly and manufacturers who's business it was to supply spray painting or other equipment. CIG Arnold always printed a booklet which showed how the plumbing should be routed around and workshop all TAFE colleges were built to the same requirements. It was always considered that if you were to preach what was correct that your shop and equipment should reflect that. TAFE colleges had top equipment spraybooths etc long before industry came on board.

The motorbike magazine used the sketch of the piping system I attached is from "Sharpe Industries" a Graco Company which I thought was reguarded as a major company.

If any readers are confused about any statements made in this discussion they should check with the manufacturers data sheets or their technical advisers as to what is the correct and acceptable ways, Thats what I've always found to the most sound method to obtain good results.Then make up your own minds as to which is the best.

Maybe a plumber would like to reply to the comments Soundman has on copper pipe I was under the impression water pressure could be a lot higher than what can be pumped into a compressor - but I might be wrong again.

i am still following this with interest
the differing points of view is providing a wealth of relevent info i was totally unaware of
feel free to battle on if you wish

I know precisely what phosophoric acid is..........however most of us mere mortals will have quite a bit of difficulty getting hold of it these days in unadulterated form.......last time I tried to get some I was told that it is a controlled substance as it can be used to produce both drugs and poison gas ( the stuff they let go in tokio subway I understand).

most of us have to put up with getting it packaged around 30% dilution and contaminated with resins or something else packaged as "rust converter".
If you can tell me where I can get a litre or two unadulterated I would like to know.

I have and still do use it, it is great for getting plating off screws so you can get paint to stick to them, and it may be usefull for removing very light oxidisation, but the notion of "converting" any volume of rust or scale in my experience s no more than sales hype.

We have always been sold the idea that the phosphate coating give some measure of protection.......in my experience and that isnt in the hygeenic and strictly controlled factory situations.......that protection is short lived....phosphates by their very nature are reactive substances......it is my impression that after a period and in the company of moisture the presence of the phosphates or whatever they degenerate into actulay prometes corrosion, particularly if there is remaining unreacted iron oxide.

If slucing metalwork with phosophoric acid is so common place how come I have never seen or heard a panelbeater performing the practice..........the better ones just sand solvent wipe and etch prime.
I've heard of plenty of hot rodders snadblasting or hand scraping bodies back to bear metal but I cant remember hear of one getting a body acid dipped...after it was clean they etch prime very promptly

In this day and age of OH&S I recon they would be scared $###less of a big pool of acid

anyway... back to the original point....unless your compressor tank is full of scale & carp there is no point even bothering to clean it.......the water drains out the bottom taking most of the carp with it.....the air comes in and goes out the top of the tank.....the particles at the bottom of the tank are most unlikly to come out the small hole at the top.

If your compressor tank has heaps of scale in it.....its time for a new compressor......my current main compressor is now over 12 years old, it is powered up from 7am to 7pm 7 days a week regardless.....when I drain the tank ( which I should do more often) i get some frothy water with a little oil in it and perhaps a slight taint of rust toward the end....ocasiolnaly there will be the slghtes bit of gitt in the bottom of the bucket....I look I feel.......I suspect no rampant corrosion.
I have seen rusty tanks with pinholes but they started out very thin anyway and they were abused......there are many tanks out there many decdes old, they don't seem to have rusted away.

It occurs to me that the average small compressor is more likley to die a mechanical or electrical death before corrosion becomes a problem...... particularly the cheapies.

lets not confuse small workshop practice with major manufacturing.

now I have seen workshops where every air pipe that comes down a wall continues past the air outlet to a drain cock........I dont think this will happen in a small workshop

regardless of who said what......please tell me why it is a good idea to have water running toward your air outlet.

then can you tell me why it is a bad idea to have condensed water drain back into the compressor tank where ther will always be plenty to go with it..

now on the matter of copper pipe and air.

Normal reticulated water will very rarely get above 45 psi standing preasure, in fact many appliances such as dishwashers warn that they may malfinction at water preasures over that point......in fact 10 to 15 PSI would be more normal..... otherwise you would have holes drilled in you back by the shower, and rinsing the dishes would be a lot more fun.

now consider that the air pipes and tanks in my small shed run at arround 90 to 110PSI and many industrial systems run well above that. Most factories running air powertools will want at least 110PSI post regulator at every work station so to achieve that reliably they will need to run 120 to 180PSI in their main airlines......that is a large amount of air preasure and an enormouse amount or storred energy.
Standard plumbing copper is simply not up to the task, plumbers will use approprate copper and you will easily buy appropriate copper, but it isn't anealed, it does not come in a roll and it does not have a seam........it comes stamped with a standard number and is quite a bit more expensive that standard copper.

cheers

Hi O-P here is some more for you to think about.

Soundman obviously took me to literally, I mentioned the using of Phosphoric acid thinking as Old Picker did that I was talking about a metal conditioner or converter. Which I was. You just have to go to your hardware store, supercheap or other auto store Bunnings or automotive paint trade or retailer store. These materials will work fine.

Full strength PA is not suitable to neutralise rust . Even in its retailed form it has to be diluted with water to use correctly. Depending on the brand this could be between 2 to 4 to One part concentrated product.. The products by the way have detergents and other additives to help wash and clean other impurities on the steel the PA neutralises the rust the others remove dirt and oil etc that may be present so the steel is cleaned properly to allow it to be painted. Yes it has to be done within a short time ( about 30 min) and the instructions say you must not touch the metal as you may contaminate it as perspiration with introduce moisture again which will start the rust process.

Using PA conditioner is an important part of the steel painting process, you don't have to use it but if you don't you have the worry that the steel is not rust free. Paint over it and you may find further down the track that the paint blisteres. I'm sure many of you have seen rust blisters under paint even hand or finger prints in the form of rust.

If you leave the metal exposed for even a short time rust will start. If you stripped a car of all paint and didn't take the few minutes to treat the bare metal with PA metal conditioner you are an idiot. Just imagine doing all that work stripping off the paint repainting it and then finding down the track that the metal is rusting underneath. As this would be an expensive job you can bet the owner would be coming after you. In NSW painters have to be licenced and if such a situation came up they would be required to appear before the court to explain why they should not be required to redo this job again at their cost.

Paint companies now have equipment that can determine exactly what you did to any paint job. It can tell what if any metal conditioning took place what products and whose thinner was used.

Miss one of the correct requirements ( say you used a different brand of solvent or hardener) and they excuse themselves. Painted didn't follow correct proceedure cost payed by him. I don't know why Soundman doesn't know of any panel beaters who use Metal Conditioner probably because it would be their painter who would be doing it not them. If a panel beater sanded off paint to repair a panel a painter would always asume that he has put his dirty greasy hands all over it and left the bare metal exposed to the air for a number of hours while he worked on the job.

There is not one repair shop in the Illawarra that does not use this conditioner only shop I know of who doesn't only does second hand work. So they would consider that their chances of a car coming back to be zero. Botttom line it has always been required to wipe bare steel with metal conditioner before applying primer, you can do it any time but its usual to do it immediately after solvent wiping and before priming. It takes a few seconds to do on a small spot a few minutes on a big job, lots longer to repair the paint if rusting takes hold under it. Not worth the risk for a good business.

Soundman mentioned that some primers contained PA. It helps adhesion but also adds to the equasion in preventing the metal rusting. One company ( Wattyl) had a primer and its instructions were to only scrape off loose flaking rust particles from the steel and to paint it over the rust as it would handle that done by metal conditioner. I never used it that way, scarey advice having seen what some people do when using paints.

I have attached a picture of a piece of sheet metal which has been in my outside steel bin for a few years now. It has been washed over with mixed Metal conditioner (Du Pont) with a rag. The picture was taken next day (about 14 hours later ) you can see the difference. Would you like me to just sand the rust or wipe it with the PA? I know which one I'm happier with. Next to it is the rag I used to apply the PA and also a carburetor bowl which is treated with a rust converter . Unfortunately I don't know exactly how long ago that was done as its more than 12 years it was sandblasted and wiped with the converter awaiting painting. I didn't use it as I opted for a bowl with a drain tap in the bottom. About 5 years ago I found it in a box of other bits and put it on a shelf to see how long it would be before it rusted. Its been handled by a lot of people and its so good still that I would just give it a wipe with solvent before paint it now.

In the mid 1990's the industrial painting trade was bought to account by the NSW government. People were having large steel structures made ( cranes etc) worth many millions of dollars and they were turning into rusty relics in short time. Owners of these machines etc lobied the Govt to set up a course so that workers could become qualified to apply a proper paint system for the machinery. One of my co workers was responsible for the development of the course. Now if you need such a product made you can write into the contract that you require it to be done to the standards set and that those applying it be certified. If the paint fails the stipulated guarantee the industrial paint applier can be held accountable. If he thinks its the paint the paint company will be involved. They arn't going to pay out big money unless they have too . As these products are usually made from steel sections which are usually rusty even when they are delivered sandblasting and metal treating is part of the proceedure. Part of the reason for the course is that often those doing the job didn't know that it was required and the bosses often didn't supervise or thenselves thought it wasn't necessary. ( or were cutting corners.) You can bet that treating with metal conditioner is part of the course.

Now compressed air lines.. I still say Soundmans wrong. If the air is compressed it heats up water turns into vapor and back into water when it can cool down. It may leave the tank as vapor if it travels up the wall it may cool to water. So the vertical pipe should have a tail down past the compessor outlet to enable the water to fall down to the bottom so it can be drained off . Not much use going back to the tank as the airs trying to rush out of there and will take the water with it. If it gets to the top of the pipe and hasn't cooled down it now will not turn to water further along the horzontal pipe and drop to the bottom of the pipe. The air will be able to move along above without it. If the pipe made the water run back to the tank its going to be pushed forward by the air going the opposite way. If it is allowed to proceed forward in a horizontal pipe sloping away from the tank ( suppose that means its not horizontal . but I think you get what I mean) it can run run to a downward pipe to a tail and again be drained off . If you want to only get the air out of the horizontal pipe you take it out from above so the water can't go there. add a U and you have a vertical pipe down the wall which you can again drain off the water. If you need to use air in that pipe then you pipe to an air transformer as in the attached photo.

Hope thats enough homework for the day old Picker

PS. I live 100 meters from the beach and I just checked the panel again still looks the same no rust yet.

Originally Posted by durwood

You could rinse the inside of the tank with Phosphoric acid this will kill and clean the metal so when the acid being tipped out is clean you know its good inside. Unfortunaltely its a tempory fix as water once on the metal will start the rusting again. Your compressor motor should add a small amount of oil into the tank which will slow the rust down but I would not be putting extra into it as oil will mess up the air and can get through to your paint or oil up your filters quicker.

I don't really want to buy in to the (very wordy) arguments presented here. I have to say though that I did raise my eye brows somewhat when I saw that statement!!!!

I don't know how Soundman, or Old Picker, could take that advice any less literal than that. There is no mention even of diluting the Phosphoric Acid.

It illustrates that we have to be very careful with what we recommend to people, they will see that statement, perhaps some months down the track, and act on it with possible disastrous consequences.

They will not necessarily wade through the next few thousand words to see a "sort of" retraction to the effect of "that's obviously not what I meant".

I have taken the liberty of editing your post Durwood and changed Phosphoric Acid to "a proprietary Phosphoric Acid based metal pre-treatment", just to be on the safe side and protect both compressor tanks and people.

I also have a Bunnings Special compressor and this problem has been exercising my mind lately. I wonder if some fish oil based Killrust poured in through the inspection hole and rolled around inside before draining the excess back out would work. I have used this product before and it sets to a fairly hard film after a while and shouldn't mix up with the air. What do you think?


If at first you don't succeed - your running about average!!

Ahhh now we are talkning about DUPONT proprietary product, not unadulterated phosophoric acid..........I entirely expect that that product will have resins and other corosion inhibiting products in it apart from phosophoric acid.....and if you are going to pay the premium that a company like DUPONT or 3M would charge, you would expect there to be lots more in the product than phosophoric and a bit of detergent.

also if you are talking about proprietary paint system... that to is a very different thing than "normal practice".

as I said before most people I have encounter would solvent wipe and immediately etchprime....in this situation there would be no more opportunity to for corrosion to set in than if it were treated by some proprietary product.

any way in this situation we are not talking about a auto refinish application...we are talking about removing scale from the inside of a tank.

on the matter of fishoil or whatever.
most of the corrosion prevention treatments ( except sacrificial treatments such as plating) we see are aimed at preventing aiborne moisture or transitary moisture from accessing the metal.
when you immerse such treatments long term they will eventualy fail to perform their function, corrosion will set up under them and the whole thing goes pear shaped..... combine a preasurised environment it cant go well.
Oh BTW ordinary oil will do very little to prevent corrosion if the metal is immersed in water, the moisture will very easily get thru the oil and so will the oxygen.

my view is that the best thing you can do for you compressor tank is to run the machine regularly and drain the tank frequently........a great many tanks provide very long service with nothing more.

On the matter of water flow......it must be understood that the amount of fluid condensing in lines is very very small......so there is no real flow...it just accumulates steadily over a very long time......for that matter the moisture will only settle out during idle times.....particularly if the lines them selves and the air in them is allowed to get warm or hot.

we can argue about which way to slope your lines till the cows come home......but the important thing above all...is that air lines should slope toward somewhere where water can be held and drained off.
That is unless you can achieve a pretty damn dry air stream before it enters your pipe system.
In reality most of us that do have a pipe system will have a few meters of pipe and less than a dozen outlets.

As i said before....since I fitted a second tank followed by an ordinary filter reg....I have had not a spec of moisture out of my lines..not a spot, not a droplet, not a whisp.........all you need to do is slow the air down and allow it to cool, and let your filters do their job .
this works regardless of you having a plumbed in system of just one hose.

It is possibly the single simplest and best improvement you can make to a compressed air system of any size.....and the second tank does not need to be large.....

cheers

Point taken Big Shed, When I made the statement I was naturally thinking proprioetry line. As Soundman mentioned previously neat Phosphoric Acid can't normally be obtained and I it never occured to me at the time that anyone would attempt to track down and use it - if they could.

I didn't further elaborate on the process as I assumed if picker wanted to go that far he would have asked more about doing it or would get a normally available product and follow the instructions on the label to dilute for use.

Neil, forget the fish oil it will eventually end up coming out as other " little black Bitties" also,
just keep the tank drained.

Big Shed your right about the ( very wordy) arguements also, one thing that forums haven't been able to do real well is collect all the direct answers to peoples questions they get lost amonst all the banter. Someones going to ask a similar question in the future and " search " will leave the poor guy with so much to go through.

Everyone reading will have to come to their own conclusions about what has been discussed.