Air Supply

Nov. 1, 2000
Getting the most out of a compressor depends largely on air quality.Compressed air always has been a major source of energy for work in construction and

Getting the most out of a compressor depends largely on air quality.

Compressed air always has been a major source of energy for work in construction and industrial applications. Both oil-flooded and oil-free compressors provide the right solutions to the many rental applications requiring compressed air. The pressure and volume of air required are key factors in choosing a portable compressor for the application.

For many contractors the "quality" of the air provided is also an important consideration. "Quality of air" can be defined by how dry, clean and free from contaminates the air is. Dirt, oil and water can be detrimental to many processes and applications. If a rental store sends out a compressor that doesn't handle the job requirements properly, it could influence future business.

Rental compressors Oil-flooded, or lubricated, screw compressors are among the most popular types of portable compressors for many construction and industrial applications because of their low cost to purchase and operate and their wide range of flows and pressures: typically 90 to 1,800 cubic feet per minute and 100-350 pounds per square inch gauge. They are also among the most popular pieces of equipment in the rental yard. The air produced by these compressors is saturated with water vapor and has a level of oil and particulate carry-over that might not be acceptable for some applications.

Oil-free, or dry, screw compressors do not add oil to the compression process. However, the compressed air is only as clean as the inlet air that is ingested through a 10-micron inlet filter and is saturated with water. Because these are diesel-driven compressors, the air around the compressor is highly contaminated with hydrocarbons and particulates. Oil-free compressors typically are used in applications such as pharmaceuticals, electronics and food processing in which the validation process requires their use. These compressors typically cost twice as much as oil-flooded compressors.

Clearing the air A combination of aftercoolers, water separators, dryers and filters is used to clean and dry compressed air. It all starts with the air from a compressor, typically registering temperatures from 200 to 300 degrees Fahrenheit. Cooling the air via an aftercooler significantly reduces the amount of moisture in the air. A 20-degree reduction in temperature can condense half of the water vapor in the saturated air from the compressor. Once the water vapor condenses, the water is collected and eliminated with a water separator.

Dirt and other solid contaminates are removed through filtration. Oil and additional water in aerosol form are also removed. The filters used to remove these contaminates are combinations of particulate and coalescing filters. Filtration levels typically can be provided down to 0.01 microns in size for particulates and aerosols.

Depending on the application, a dryer also might be needed. How dry your air needs to be is determined by the dew point required for the specific application, and this requirement determines the type of dryer needed. The most commonly used types of dryers are deliquescent, refrigerated and desiccant. Dryers might be required with oil-flooded or oil-free compressors.

The combination of equipment used with a compressor can provide what industry standards define as instrument-quality air. Instrument-quality air is a viable alternative to oil-free air in many industrial and construction applications, including process air, instrument air, painting and abrasive blasting.

Selecting the options This additional equipment required to improve the quality of air with compressors should be an option that rental centers look for in stand-alone units. Compressors are also available with built-in aftercoolers, water separators and particulate and coalescing filters. Some compressors with these built-in features are available with a condensate removal system that provides environmentally friendly operation. The oil and water collected from oil-flooded compressors cannot be dumped on the ground for environmental reasons. Normal collection and disposal of this effluent are time-consuming and expensive. The condensate collection system burns off all effluent by injecting it into the exhaust system, eliminating costly disposal.

These built-in features allow quick setup at the rental site and can eliminate the need for additional equipment at the site. The compressors also offer flexibility to the rental yard. These units can be used as a standard oil-flooded rotary screw or easily can be switched to provide cooler, cleaner air, depending on the rental application.

More and more applications today require cooler, cleaner and dryer air - a higher quality of air. These varied applications can provide more and more rental opportunities.

Whether the compressor is used for providing clean, dry air for abrasive blasting or painting, snow making or keeping an industrial facility supplied with primary air while repairs or maintenance is done, a higher quality of air is required in today's rental market.


The Ultra TG-280 is a gas-powered, 5.5-horsepower air compressor designed for continuous operation on remote job sites, according to Thomas Industries. It delivers 8.5 cubic feet per minute at 100 pounds per aquare inch and allows for multitool use from the single unit. This twin-piston compressor has a Perma-Lube oil-less design for quick cold-weather starts and twin 3.5-gallon air storage tanks. Other features include a Honda engine with a cast-iron sleeve, an electronic ignition, an overhead valve design and a large fuel tank.


Selected models of Kaeser's Mobilair portable air compressors feature new options. The M56 and M76 (pictured) now feature a 7.2-kilowatt generator with two 120-volt receptacles or two 240-volt, one-phase fused outlets. The M56, M76, M120 and M260 have an aftercooler/filter option that provides a reliable source of clean, dry air, the company says. Mobilair standard features include the power-saving Sigma Profile air end, a cold-start battery, fully galvanized steel enclosures, a torsion bar suspension system and a Deutz diesel engine. The M76 is a 200-cfm unit.


Mi-T-M's AC2-SV09-20M stationary, two-stage, 20-gallon air compressor features a 9-horsepower Vanguard OHV gasoline engine with an optional electric start and a 15.7-inch flywheel for extra cooling during extended use. Other features include a two-stage compressor head, an aluminum head and crankcase with a cast-iron cylinder, and a 14-gauge powder-coated belt guard. The 20-gallon receiver is an upgrade from the previous 4- or 5-gallon receiver.


Featuring an on-board aftercooler and filtration system that delivers clean, cool, dry air with no condensate discharge, the IQ System series of rotary screw air compressors has models rated at 1,300 (pictured), 935 and 300 cubic feet per minute from 100-150 pounds per square inch gauge. The valve system allows operation as a standard rotary screw compressor or in the IQ System mode for instrument-quality air, Ingersoll-Rand says. A shutdown feature prevents air system contamination. The unit's Cummins diesel engine is rated for continuous operation at 460 brake horsepower.


Sullair's portable compressors range from 110 to 1,900 cfm at 100 to 350 psig. The utility compressors, designed for cross-mounting on utility-type trucks, are available in 100 to 250 cfm at 100 to 150 psig. The power takeoff units are completely contained within a service truck's dimensions. All compressors feature the company's rotary screw air end.


Powered by a John Deere 4045T diesel engine, Sullivan-Palatek's D375Q7 air compressor provides 375 cfm at 70 to 125 psi in a 3,400-pound package. The full instrument panel includes an alternator indicator, an hourmeter, an unloading valve, a bypass switch, an ignition switch, and gauges for fuel level, discharge pressure and engine water and oil temperatures.


The 2001 models of GrimmerSchmidt's air compressors have these new features: side-by-side radiator/oil coolers, stainless steel exhausts, larger tool storage compartments and simplified controls, the company says. Standard features include large diameter air ends, large receiver separators, full-gauge instrument panels, combination ball/pintle hitches, lifting bails and easy-lube wheel bearings. 800/428-9703

Atlas Copco

Rated at 185 cfm at an operating pressure of 100 psi, the XAS 96 JDU utility mount air compressor minimizes the space required for mounting with a compact canopy design, according to Atlas Copco. Removable side panels and a rear hinged door facilitate maintenance. Other features include compressor and engine oil drains, fluid fills, oil/air filters and an engine oil dipstick. A John Deere diesel engine powers the unit.


The Genair Series of air compressor systems enables a truck's engine to generate pneumatic and electric power through the power takeoff drive, Vanair Manufacturing says. Each unit is completely contained within the vehicle's frame rails and combines a brushless, 5.6-kilowatt generator and a 125- to 160-cfm compressor. The Genair system couples directly to the extended rotor shaft air end, providing constant power input without belts or gear drives. The system can be driven as a side-mount PTO or a split-shaft PTO compressor system, and the Genair and compressor can be used simultaneously.


Hankison's compressed air treatment system includes an aftercooler with air-driven fan motor, a separator, a coalescing oil removal filter, a 1-micron particulate filter and a twin-tower pressure swing desiccant dryer that operates at 12 volts, direct current. The system takes high-temperature air directly from an air compressor and produces air with a -40-degree or -100-degree pressure dew point and removes liquid oil aerosols and all solid particles 1 micron and larger, the company says.

CompAir LeRoi

The King, Crown and Predator series of portable rotary screw compressors offer the following diesel engine options: Caterpillar, Cummins, John Deere, Perkins or Detroit Diesel. The King units provide 100 to 375 cfm at 100 to 150 psi, the Crown units feature 600-1,600 cfm at 100-150 psi, and the Predator compressors offer 900-1,100 cfm at 150-500 psi.


The M800-HC4V, a 2-horsepower, hand-carried air compressor, is a new addition to Emglo's Master Series. The unit features a lightweight stacked tank design and a standard Master Series air control panel.