The Impact and Importance of Compressed Air - Tire Review Magazine

The Impact and Importance of Compressed Air

Air compressor pressure pumps

Compressed air is the energy source for most shop equipment and many tools. Inadequate airflow or pressure interrupts work flow just like an electric power outage would. Here’s some advice for choosing and maintaining your compressed air system.

Pressure Pitfalls

Avoid a common pitfall – don’t over-pressurize. Very few tools require pressures above 100 psig. Many shop owners ask for high pressure because they’re most familiar with piston compressors, which operate on a wide pressure band to allow the unit to shut down and cool. Another reason for operating at unnecessarily high pressures is that it provides additional storage. This is true to an extent, but keep in mind that compressors generally produce less volume at higher pressures and that leak losses increase with pressure. Refer to the tool manufacturer’s manual to determine your shop’s exact pressure and flow requirements.

Flow Requirements

Compressor size isn’t determined by pressure requirements. It’s determined by the compressor’s output capacity in cubic feet per minute (cfm). To properly size your compressor, you need to know how much air is needed in terms of volume, not pressure. Some tool and compressor manufacturers publish charts with air consumption rates. Adding all of these together for the tools you use yields the total potential flow requirements. But it doesn’t take into account the percentage of time each tool is used. This requires some analysis of how the different parts of your shop operate throughout the day. Electronic data logging devices are a convenient way to measure and record compressor usage.

Compressor Type

A piston compressor may provide adequate flow for a short period, but its allowable duty cycle must be considered. The duty cycle is the percentage of time a compressor operates without the risk of overheating and causing excessive wear to the compressor. Most small shop piston compressors are air-cooled and have an allowable duty cycle of 60-70%. For this reason, they’re often oversized and operate over a wide pressure band to allow the compressor to frequently shut down and cool off because of the relatively high operating temperatures (often 300-400° F).

Rotary vane and screw compressors have closed-circuit, thermostatically controlled cooling systems that provide a 100% allowable duty cycle with operating temperatures of only 170-200° F. This is an important consideration for moisture-sensitive applications, since hot air carries more moisture. The higher the compressed air temperature, the more moisture is carried in vapor form through the system. An important rule of thumb is that every 20° F decrease in temperature cuts moisture vapor content in half, making it easier to remove moisture from your system.

Air Storage

Air storage tanks (receiver tanks) provide the first stage of moisture separation, store air for short periods of high air demand, and allow the compressor to shut off to save energy and prevent piston units from overheating.

When selecting a tank:

• Allow 2 to 4 gallons per cfm.

• Be sure the tank pressure rating exceeds the highest possible system pressure.

• Be sure the tank has a safety relief valve, a pressure gauge and a drain to remove liquids.

• Be sure it meets ASME or other required codes (check with local authorities).

Dryer performance is stated in terms of specific conditions (ambient temperature, compressed air inlet pressure and compressed air temperature).

Refrigerated dryers employ a refrigeration system to lower the compressed air temperature below the ambient temperature. This condenses the moisture that’s in vapor form at higher temperatures into liquid form that can be drained out of the system. This lowers the “pressure dew point” of the compressed air. As long as the compressed air isn’t cooled below this new dew point, any remaining moisture will remain in vapor form. Refrigerated dryers are designed to produce dew points between 35° and 50° F at rated conditions.

High-temperature refrigerated dryers are similar to standard refrigerated dryers, but include an aftercooler and are primarily used with piston compressors, since the air must be pre-cooled prior to entering the dryer. These are usually designed to achieve dew points of 50° F at rated conditions.

Desiccant dryers work by directing the compressed airflow across a bed of desiccant material that adsorbs moisture vapor out of the air. They are used to produce dew points as low as -100° F and are recommended when air quality requirements are extremely high.

Filters are categorized based on the contaminants they’re designed to capture and may be designed to capture more than one type.

• Moisture separators are designed to mechanically separate liquid water and oil from the air stream.

• Particle filters are designed to capture dirt, dust, etc., but may remove some water and oil mists.

• Coalescing oil filters are finer filters designed to remove oil aerosols/mist and fine particles. These are usually placed after a refrigerated dryer.

• Vapor adsorbers are designed to eliminate oil vapors only and should be placed after all other filters and dryers.

• Staging the filters in a system provides more effective filtration, lower pressure drop at each filter and longer filter life. Some have differential pressure gauges, liquid level indicators and built-in drains.

Keep in mind that filters also need drains and that differential pressure gauges will indicate when the filter elements need to be replaced. Periodic filter changes will minimize pressure drop and ensure good air quality.

Condensate drains/traps are critical but often overlooked components. Drains remove liquid contaminants from the system. If the filtered and separated contaminants (mostly water with some oils and particulate) aren’t drained and removed from tanks, refrigerated dryers and filters, they build up and find their way back into the air system. Liquid accumulation in tanks will gradually eliminate the air storage capacity in the tank, causing periods of inadequate air flow/pressure and possibly causing a reciprocating compressor to exceed its duty cycle and overheat.

Several types of drains are available: manual, timed and automatic demand (a mechanical or electric device that activates when the liquid level reaches a certain point inside the drain). Invest in quality drains to protect your investment in filters and dryers.

A thorough analysis goes a long way in building a reliable, cost effective system. Carefully consider each system component and its impact on the application. And remember: Value is more than initial price. Purchasing quality equipment now will save time and money for years to come.

It’s a Dirty Business … Clean It Up

Water/moisture – usually in the form of vapors, mist or liquid – may:

• Cause excessive wear in tools.

• Freeze in pipes.

• Cause rust in iron pipes.

• Reduce the volume available for storage and cause piston-type compressors to run beyond the recommended duty cycle.

Adapted from an article in TechShop – adapted from an article in BodyShop Business

You May Also Like

Understanding New R1234yf Refrigerant

The R1234yf refrigerant that will be required in all new cars next year has actually been found in vehicles since 2014 when Chrysler began using it in the Dodge Demon and Jeep Trackhawk, among others. Unfortunately, it’s difficult to tell with certainty how many vehicles already have R1234yf due to the phasing in the process


The R1234yf refrigerant that will be required in all new cars next year has actually been found in vehicles since 2014 when Chrysler began using it in the Dodge Demon and Jeep Trackhawk, among others.

Unfortunately, it’s difficult to tell with certainty how many vehicles already have R1234yf due to the phasing in the process over the past 10 years – some estimate it is already well over 50 million vehicles. It is not a question of if, but when you’ll have to deal with this refrigerant. While working on R1234yf systems is not that different from the R134a variety in operation or theory, identifying the refrigerant and recharging the system has some new twists.

Education on Tire Life Improves Tire Longevity, Customer Trust

Don’t you wish everything aged like a fine wine? While that dry red gets better as the years go on, we humans are subject to old age and wrinkles and our great inventions like cars get rusted and worn out. Tires on those cars get worn out, too. Like our bodies, the more miles you

What’s Next for TPMS Technology?

TPMS, like most technologies, is always evolving, and that is a good thing. The more accurate the system becomes and the more features that are added to a TPMS system, the more likely the driver will find value in keeping their TPMS system functioning. In the past 10 years alone: Related Articles – Don’t Let

Servicing Tapered Wheel Bearings

You probably haven’t seen tapered wheel bearings in many late-model vehicles. It seems that nearly every vehicle made these days will run some sort of wheel hub assembly. There are a number of reasons for this, but the biggest reason is this: ease of assembly. Not assembly for those of us that work on these

tapered wheel bearings
Replacing Weak Springs

No road is entirely flat. Even a small tar strip or dip causes movement in the suspension. This movement is controlled by the spring and dampener. No matter the type of movement, the spring is compressed and then releases the energy into the body, dampener or road. Related Articles – Catalytic Converter Theft: How it

Replacing springs

Other Posts

How Can Cars Communicate With Your Shop Equipment?

OEMs do not just manufacture vehicles out of steel, rubber and plastic. They are producing code for software or firmware at a staggering rate. This code is hardly ever finished. As vehicles in the field rack up the miles, they will update the code to cure problems the engineers did not originally anticipate. Related Articles

Tesla Model 3 TPMS Service

One of the first items to be replaced on any Tesla model are the tires. This is due to tire wear from the instant torque of the electric motor. When replacing the tires, you will have to service the TPMS sensors. Related Articles – Don’t Let Electrification Shock Your Shop – What Data Tells Us

ADAS Calibration: Sensor Operation & Calibration Myths

Do you know what happens during an ADAS calibration? Or why it is a must with today’s high-tech vehicles? Many shops and technicians can come up with multiple reasons why they don’t want to perform ADAS calibrations or invest in the equipment. But, chances are, it’s because they don’t understand what happens during an ADAS

CV Joint Replacement Tips

Constant-velocity (CV) joints have been around since the 1980s when front-wheel drive (FWD) came into widespread use. Related Articles – The Costly TPMS Mistake You Don’t Want to Make – TPMS Diagnostic Strategy and Checks – Charging for TPMS Service Although some rear-wheel drive (RWD) and all-wheel drive (AWD) vehicles also use CV joints, most