Auditing Compressed Air Quality

Just as you would not drink dirty water, purchase gas that did not burn, or pay for electricity that couldn’t light a bulb, a welding shop cannot be run on contaminated compressed air. Many welding shops don’t assess the true cost of their compressed air, supplied, in many cases, by an aged, overworked and underpowered air compressor. An underperforming air system will manifest itself in ways that are both obvious and not so obvious. We can all understand the effect of air leaks on the cost of operating an air compressor, but how about the productivity losses due to wet, dirty, oily air? While not as easy to quantify, these costs can easily exceed the cost of operating the system.

No one likes an audit. They generally involve time, expense and dealing with things we’d rather leave alone. But an audit of the air quality in a customer’s shop can be a very rewarding exercise that will yield immediate results not only for the customer, but for the distributor/supplier to that customer. In fact, the Compressed Air & Gas Institute estimates that a simple walk-through evaluation can save your customer as much as 25 percent on energy and maintenance costs.

Effective Air Preparation for the Welding Shop

Remove water and dirt to 5 microns, not 30 or 40.

Remove all remaining contaminants to .01 micron, not just oil.

Remove water vapor to -40F dew point; use silica gel desiccant.

Remove oil vapor to <.01 ppm for critical finish applications.

Regulate the air with a real diaphragm regulator, not a “cheater” valve.

The following is a guideline for a Compressed Air Quality Audit, a simple one-hour exercise that will pinpoint just what needs to be repaired, replaced or installed to ensure the entire shop is provided with clean, dry, oil-free air. Steps as simple as rerouting some drops, increasing pipe size on a run, or adding some point-of-use filtration can have a huge impact on air quality.

Step 1: The Air Compressor
The air compressor is the heart of the system. Can it supply the shop’s demand, all day, every day? A rough CFM (cubic feet per minute) requirement is to add up all the air tools, blow guns, blast cabinets, plasma cutters and other devices that are powered at one time. The CFM requirement is listed on each tool or can be found online. Calculate the total, divide by four, and that is the approximate horsepower required from the compressor.

Need more horsepower? You can remove some of the tools that run at once or add another parallel machine to raise the total HP. Or maybe it’s time for that new piece of equipment. Compressors can be simple, reciprocating (piston) devices, more efficient rotary screw devices, or multiple zoned parallel systems for optimum output supply. New compressors can radically reduce operating and maintenance costs as well as noise. A common problem on old compressors is lubricating oil that blows by worn piston rings contaminating the system.

Step 2: The Distribution System
Can the compressor supply the shop’s demand for CFM? Is it large enough in diameter? A 25 HP compressor will put out approximately 100 CFM, requiring a 1-1/4 inch diameter pipe for a 100 foot-length run.

Another important aspect of the shop piping system that might require some attention is the physical layout. A loop design will shorten the distance to the furthest drop, thereby getting the job done with a smaller diameter pipe. Other points of the audit include ensuring that the compressor receiving tank is the lowest point of the system, that there are drains installed at low points and that all air drops come from the top of the pipe.

Step 3: The Filtration Components
The primary source of contaminants introduced into the shop air system is the compressor itself. Dirt and moisture are drawn directly into the compressor from the surrounding air. Check the intake filters. Are they in place? Are they clean? The bulk of the contaminants can be trapped at the source with a properly sized water trap, particulate and oil coalescing filter mounted near the compressor. A tank-mounted automatic drain will automatically remove all condensed water from the tank before it can enter the piping system. A real shop requirement in high humidity areas is a refrigerated air dryer. Couple that with an after-cooler, and you have taken care of the primary source of unwanted water.

Common Air Preparation Myths
Categorize each department’s filtration requirements and address each problem area. Doing so  will address some of the common air preparation myths listed below:

Myth: Air tools run best on dirty air.

Reality: Stray oil from a compressor is too heavy and too full of moisture and contaminants to be a source of air tool lubrication and can gum up air tools and cause corrosion and wear. A 40-micron particulate filter/water trap installed at the tool has shown to double tool life. Where inline lubrication is needed, add an oiler.

Myth: The welding shop doesn’t need clean air.

Reality: Blowing off the work with contaminated air forces oil aerosols onto the material, which contaminate welds and foul plasma cuts.

Myth: Plasma cutters come with all the filtration they require.

Reality: Contaminants in the compressed air system—dust, scale, condensed moisture and oil mist—seriously affect the quality of plasma cuts. Installation of a submicronic filter on a plasma machine will effectively remove these contaminants, eliminating arc sputter and producing cleaner, faster, smoother cuts. As a side benefit, this also prolongs the life of expensive electrodes and tips.

Gases and Welding Distributors Association
David Barleen Meet the Author
David Barleen is president of Motor Guard Corporation, headquartered in Manteca, California, and on the Web at