Airline Information

 

So, you want to paint.  Just hook up a hose to the compressor and go!  Hold on a moment.  Lets look at your air supply.

To paint, we need 3 things. 

  1. Enough air to supply your paint gun, which can be up to 15 CFM.  Read your paint gun documentation to find this out.

  2. Clean Air, good filters go down to 0.01 micron 

  3. Dry Air.

Lets start with enough air.  A large HVLP paint gun can take up to 15CFM.  This requires a GOOD 5 hp to supply if the project is large.  If you are doing a small project than your tank may have enough reserve to get you by.  Adding an extra tank can help a lot.  This is a trick we do to help borderline shops get by.  Adding more airline will also add more storage.  For more information on paint gun cfm requirements/tips, visit this page.  Adding a additional storage tank can also aid in cooling the air, more on this later.

Once you have a compressor that is rated for the paint gun that you have, now we have to get the air from the compressor to the paint gun.  Your airline is like the exhaust of a vehicle.  If you have one restriction, you are doomed.  You want it to be free flowing.  The larger the better.  Piping, for a hobbyist I would recommend a minimum of 1/2 inch, preferably 3/4.  Hose, 3/8 INSIDE diameter and do not run more than 35 feet or you will see excessive pressure drop.  Fittings, full flow HVLP fittings are the way to go.  On ALL tools.  I don't preach brands that much, but Prevost makes the best couplers that I have seen, they are built better, flow better and even have safety versions available.  Look them up.  I have seen some cheap couplers disassemble themselves creating a huge safety issue.

So, what kind of line?

  1. Aluminum, the best especially when coated on the inside to prevent corrosion.  This will cool the best, there are systems that are easy to work with cutting down installation time, and making the systems "modular".  Yes it is costly, but it is a one time expense and the easiest to install.  Prevost also makes this type of airline, but there are many manufacturers.  Make sure it is coated on the inside.

  2. Copper, Is also great.  But it is costly and harder to work with.  Preferably ridged copper, not coiled.  Coiled will sag and cause potential low spots for water to sit and build.

  3. Steel, Has worked in shops for years.  It does have some downfalls.  First is corrosion.  It will rust.  It might not give you issues in your lifetime though.  It is also harder to work with if you need to thread it.  It is also hard to change down the road as it has to be disassembled.

  4. PVC.  DON'T USE.  It does not dissipate heat.  It will also sag causing a low spot that water will build up in.  This nice storage space for water will eventually fill up and cause huge water problems.  But the biggest issue?  Safety.  If it bursts, it will shatter.  A Xray does not find plastic.

  5. Rubber hose,  In a pinch it can be used in greater lengths, but should be temporary.

 

Now lets look at routing of the airline. 

Even professional shops often do simple installation mistakes that hurt the quality of their air.  A "loop system"  This is a great diagram found from this site. 

airline piping

Notice that the air drops off the top of the line.  This helps to keep moisture in the line to drain from your engineered low spot.  The loop allows the air to come from both directions causing less friction and less heat build up with the air.  It also allows smaller pipe to be used.

So we have enough air now.  How do we get clean dry air?

Refrigerated dryers are nice but probably economically not in our budget.  I have seen used ones go for a few hundred dollars though.  Keep your ear to the ground!

If we do the piping correctly, GOOD filters properly placed can do the job. A cheap filter that is not maintained can actually supply you with dirt........  A filter mounted to your undersized compressor, than a air hose that goes across cold concrete is a sure fire recipe for water in your paint.

In a professional installation we generally have a "mainline" filter.  A filter that filters to 0.1 micron.  This removes the big stuff.  Removes the bulk of the oil/dirt.  Generally two stages, first being a coalescing type of filter removing water by spinning the air, and removing the dirt to 3.0 micron, the second stage having charcoal in the filter to remove oil and bring the filtration down to 0.1 micron.  There is a reason we do this, if possible, it is great practice.  So you decide to purchase a filter, where do we install it?  Unless you have refrigerated dryer, a MINIMUM of 25 feet from your compressor.  50 is even better.  If you mount it too close (like right on the compressor), the air contains water and oil in a vapor form.  The water and oil must condense to a liquid form by cooling for a filter to be effective.  50 feet of aluminum pipe can cool the water and oil to a liquid allowing filters to remove them.  If the water and oil are a vapor they go through the filter, later to condense to a liquid and destroy your paint job. 

So, how can we put the filter 50 feet away from the compressor in a home shop?  Simple a wall loop.  Here is a picture of a pretty nice unit that anyone can build.

wall loop

We then add our mainline filter.  The air goes though the filter removing the bulk of our contaminants.  But now we want to paint!  It is best to get our air clean to 0.01 micron.  So now on our paint hose (which we only paint with as we don't need oil from oiled tools getting into our air hose) we add another filter.  This should filter to 0.01, have charcoal to remove oil based contaminations.

There are a number of manufacturers of GOOD air filters.  There are even more manufacturers of cheap airfilters.  If the price is cheap, it is cheap.......  I have seen cheap air filters add to the problem, not take away.  Read the specs of the filter.  Look at the filter, open it up and look at the filter element.  Here are some manufacturers of good filters.

RTI SATA Kaeser Prevost  

 

Here are a few filters that I wouldn't use or recommend.

Model 606A Air Control Unit with Filter Sub-Micronic Compressed Air Filter - 45CFM Air Filter PAI Gun Central Pneumatic 68232 3/8" Air Filter with Regulator

Sharpe 606 commonly seen, only filters to 0.1 micron but more importantly has a black coating on the inside which later flakes off and enters your paint.

Motor Guard "toilet paper" filter.  Yes it's cheap, there is a reason.  I only use toilet paper for one thing......

Filters that you mount on the gun.  If you have a good airline, you do not need these.  These restrict air flow and only will collect one ounce of moisture.  Open one up if you truly are set on using one.  If you add up the cost of these over time, you could buy a good filter.  In a pinch, I would use one.

Really cheap filters as a whole.  If you look at the filter it generally is a plastic (because bronze costs to much!) filter that is porous and allows the air though.  Is it better than nothing, yes.  Would I want it filtering the air to my expensive paint?  NO

 

Desiccant, or not to desiccant?  Desiccant is used in many high end filters.  Desiccant drops the dew point down and is able to absorb moisture.  It works and can remove most moisture in a affordable manner.  It has it downfalls, but if you understand them, they can be a good choice. 

  1. If you have lots of moisture going to a desiccant filter, the desiccant becomes saturated and no longer absorbs moisture.   Repeated replacement gets expensive.

  2. Some types of desiccant that is used on cheaper units can fracture causing desiccant "dust" in your paint if not maintained.

  3. Desiccant needs to be maintained.

  4. Desiccant can swell when saturated with moisture restricting air flow

  5. High volume filters are NEVER desiccant.

All filters need maintenance.  You should do maintenance at least annually, even more frequent if your system sees high use or has lots of moisture.  With desiccant, I would be looking at 6 mos minimum.

Here is a affordable filter that I have found.  The RTI MD4.  What is cool is that you can run desiccant while painting, and then replace the cartridge with a RTI Stealth cartridge for normal use!  More bang for your buck.

RTI Mini Desiccant Dryer/Regulator Combo

 

Hoses, there is a difference to hoses.  First off a paint hose should NEVER have oil in it.  You can get oil in it by attaching to a oiled tool.  Oil can enter the hose from the tool.  There are hoses that dissipate static electricity.  They are expensive, but so is a bad paint job.  Never use a 1/4 inch hose for painting.

 

Some cheap tips to help keep down the moisture and assist in getting good quality air.

  1. Put a fan on your compressor if you are running it hard and it is hot.  This will help in many ways.

  2. Drain your compressor frequently

  3. Drain your filters

  4. Maintain your filters.

  5. Drain your airlines (you did install a drain?)

  6. Use HVLP style "full flow" fittings

  7. Route your airlines properly

Good luck!

Home