Compressed Air Filters

[Michael Mayo]

The other thread reminded me I have been wondering about how to filter the air coming out of my big compressor. I am relatively familiar with the filters that you put inline with the output to filter out the water but i had one on my last compressor and it just didn't gather any water at all. Do any of you have any recommendations for a good inexpensive water filter device for a compressor. I am not buying an air dryer as they cost more than the compressor itself. There has to be some type of filter available that will effectively filter out the water from the air line in order to spray paint and keep my tools from getting rusty?

[Carroll Courtney]

Michael,I have acouple of filters that I installed back to back just to help out.Maybe your last filter was an oil separator instead of water separator which is also needed in an air system.To help the filters do their job,I start at the compressor keeping it drained,keep the intake filter on the compressor clean and a good brand which is like a oil filter but open type and not one of those sponge type.Grainger sells Wilton brands,Dayton or Speedair brands which are very good but not 100% without an air dryer.I work w/pneumatic controls at work and these are the things that I do to help keep moisture out of the lines----Carroll

[Matt McColley]

+1 for getting an industrial air filter/moisture seperator like the speedair brand... fair warning.. they aint cheep.

Put a 'T' at each point of your air system, with the quick coupling coming out horizontal, and then a short leg of pipe going straight down with a knife valve, so you can blow down the line.

You can run a sections of black iron or copper pipe in stepped horizontal runs (repeat 'S' pattern) with the air coming in the bottom and out the top..... then add a short verticle leg of pipe coming off the bottom most horizontal to collect the condensation and a knife valve to blow down that leg of pipe.

We run dedicated dryiers on the air supplies to our two CNCs at work, and in all honesty, I never see any water coming out of them. Even in the summer humidity.

[ray hampton]

do you drain your compressor tank every day ? how much water do you get out of the tank ? do you wait until the tank cools down before you drain the water ?

[John R Hoppe]

As a manufacturer’s rep for compressed air management systems I would like to put a few ideas onto this thread. First, assume that all air compressors will capture water, dirt, and other contamination from the atmosphere and that the water will condense out of the vapor stage as the air cools. This usually happens in the tank but also will occur in the pipe system as the air moves downstream from the tank. There are also compressor oil residues in this mix which are quite acidic or corrosive.

Next, the pipe system comes into play and since black iron pipe rusts quickly when in contact with water and acids, this rust gets into the airstream and needs to be removed. Because of this, black iron pipe is the last choice for piping systems, even though at first look it seems inexpensive. Much better choices are modular aluminum systems or copper (if you can afford it). NEVER use PVC as it can fail violently and is illegal for commercial use in the US.

To remove the contamination from the airstream, purchase a good quality filter/regulator system. For general purpose use, a 25 micron filter will work. Locate the filter as far from the compressor (heat) as possible, normally close to the point of use. That will allow the moisture to condense out of the airstream and be easily collected. If you are running tools that need lubrication, install a filter/regulator/lubricator combination with a port before the lubricator to pick off clean regulated air before the oil is added for the tools.

For paint use more sophisticated systems are normally used including filters down to 0.01 microns, oil coalescing filters, and dessicant drying systems. Contact your finish supplier for recommendations on the particular requirements for the materials you are spraying.

[Stephen Cherry]

One thing to remember is that compressors do a good job of condensing water out of the air. The water comes in from the humidity from the air, is compressed and HEATED, then mists out as the water cools. The trick is for it to mist out before your paint gun. A big air tank is the best place for this misting to occur, but for it to work best, the air needs to be cooled before it gets to the tank. Some compressors have an aftercooler for this, which cools the air on the path from the pump to the tank. You could just as well rig up something like an air to water heat exchanger running from a garden hose, or a length of copper tube, or copper tube running through a drum of cool water. NO SOLDERED FITTINGS here, and NO PVC. With the air cooled, the water can mist out inside the tank.

After the tank you would want a coalescing filter, here is a cheapie: http://www.tptools.com/Product.aspx?display_id=2730

From there, I like the plastic flexible tubing. Super easy, and super clean.

[Charles Lent]

For painting and sand blasting I use a filter that is designed to use a roll of toilet paper as the filter media (they offer a special filter roll, but a regular roll of toilet paper works fine). It catches all of the oil and water vapor very well, but you have to remember to change the roll at the end of the day. I bought it from the local automotive paint supply for about $30. I have since found and now use a refrigerated dryer, but still use the toilet paper filter just before the point of use (no longer have to change it every day though).

For painting you should also make it a point to only use a clean air hose between the final filter and your spray gun One that has never had any oil contaminated air run through it. Keep this hose only for use with your painting equipment DAMHIKT

Charley