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What is the Noack Volatility Test?

What is the Four-Ball Wear Test?

What is TBN?


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The Rotary Screw Compressor Market Can Be Confusing

Know the basics and rely on AMSOIL Technical Services for success in the field.


Mike Caruso
Technicle Product Manager, Drivetrain

In the April 2015 issue of AMSOIL Magazine I touched on the oil requirements and basic operation of reciprocating compressors. In this month's issue I'd like to cover another very important type of compressor: the oil-injected rotary screw.

Rotary screws have been around since the early 1960s and are currently the dominant compressor in industrial facilities. Outside of the factory, rotary screws have gained in popularity with many commercial operations, such as auto maintenance and body shops. They are commonly seen at construction sites mounted on trailers and it wouldn't be unusual to find an affordable 3 horsepower unit in a well-equipped home shop.

To compress air, an oil-injected rotary screw compressor relies on two intermeshed screws mounted in a heavy steel case. This assembly is called an air end. An electric motor turns one of the screws, which in turn spins the other. When compressed air is required, an intake valve above the screws opens, allowing them to grab air and squeeze it as it moves down their length. At this point, the compressor is producing compressed air. When air isn't required, the compressor goes into an unloaded state by closing the intake, allowing the screws to keep spinning without compressing air.

The electronics and sensors governing this process may be relatively complex, but the parts that we're concerned about from a lubrication standpoint are very simple. To lubricate the compressor, oil moves from the reservoir through a filter to the bearings and onto the screws to reduce friction between them and create an airtight seal. Since the compressed air is in direct contact with the oil, it travels through an air/oil separator filter to recover the oil so it doesn't leave the compressor with the air. Last but not least, the oil acts as a coolant, carrying the heat generated by compressing air to an oil cooler, which is much like a car's radiator. This is the reason you may hear some refer to rotary screw compressor oil as coolant.

Rotary screws have a gauge that displays the temperature of the compressed air as it leaves the air end. This is referred to as the discharge temperature, and the lifespan of any rotary-screw compressor oil is heavily influenced by it. There is no "normal" discharge temperature, but 180°F-195°F is common. Being substantially below this range can result in high amounts of water remaining in the machine, causing sludge and plugged filters. Substantially higher temperatures can shorten oil life, and poor-quality oil in those high temperatures can produce varnish to the point the machine won't run. As a safety precaution, many machines will automatically shut off at approximately 230°F to avoid damage and prevent fires.

Drain intervals for screw-compressor oils vary widely. Mineral oils may last from 2,000 to 4,000 hours, and some very expensive synthetics are rated for 12,000 hours under ideal conditions. The most widely accepted expectation for oil life is 8,000 hours. A vast majority of screw compressors use ISO 46 non-detergent oil, such as AMSOIL PC Series ISO 46 Synthetic Compressor Oil (PCI), to replace hydrocarbon-based oils, or AMSOIL SIROCCO ISO 32/46 to replace PAG (Polyalkylene Glycol)-based oil.

Polyalkylene Glycol is used by several compressor manufacturers. There is nothing mysterious about PAG; it is simply just another type of oil. The important thing to remember is PAG oils aren't compatible with any hydrocarbon-based conventional or synthetic oil, including our PC Series ISO 46 product. Mixing them in a compressor will at the very least require a thorough flushing with several filter changes. Lastly, understand that there may be a requirement for a higher or lower viscosity on occasion.

Our knowledgeable Technical Services staff helps our customers with compressor oil recommendations every day. If you'e ever in doubt on which oil to choose for a rotary-screw compressor, just give us a call at (715) 399-TECH (8324). Published, AMSOIL Magazine 07/15.

AMSOIL Signature Series Synthetic Motor Oil

AMSOIL Signature Series Synthetic Motor Oil

AMSOIL Signature Series Synthetic Motor Oils are formulated to meet the latest API SN Resource Conserving and ILSAC GF-5 industry specifications. AMSOIL Signature Series Oils include 0W-20, 0W-30, 5W-30 and 10W-30 and represent the very best motor oils AMSOIL has to offer, allowing motorists to take advantage of maximum extended drain intervals. AMSOIL Signature Series Synthetic Motor Oils are recommended for drain intervals of up to 25,000 miles/one year, whichever comes first (15,000 miles/one year in severe service conditions).

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Premium AMSOIL Synthetic Motor Oils offer the longest drain intervals on the market, unsurpassed protection and performance that effectively extends equipment life and improved fuel economy, saving customers money at the pump and reducing the nation's dependence on foreign oil.



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AMSOIL Synthetic Diesel Oil Articles and Testimonials

"AMSOIL INC. warrants that the use of its lubricants will not cause mechanical damage to any mechanically sound equipment when AMSOIL INC. products are used in full compliance with the company's recommendations and instructions."


AMSOIL synthetic motor oils are formulated to surpass engine test specifications, offering protection far greater than competing motor oils for extended drain intervals. Most synthetic oil manufacturers make no claim to extended drain intervals, deferring to the maintenance schedule provided by the vehicle manufacturer. With its unparalleled oil and warranty program, AMSOIL offers consumers unprecedented protection and economics.

Another AMSOIL First

More than 20 years ago, AMSOIL began using the NOACK volatility test as a comparison tool and measurement of quality. Back then, nearly every oil tested side-by-side with AMSOIL synthetic motor oils failed, and those that passed barely squeaked by. Other oil companies paid no attention to NOACK results until Ford Motor Company made it a requirement for service fill oils, validating what AMSOIL had said all along.

THE NOACK Volatility Test
The NOACK Volatility Test determines the evaporation loss of lubricants in high temperature service. The more motor oils vaporize, the thicker and heavier they become, contributing to poor circulation, reduced fuel economy and increased oil consumption, wear and emissions. AMSOIL Synthetic Motor Oil resists high temperature volatization better than other motor oils. AMSOIL Synthetic Motor Oil maintains peak fuel efficiency and reduces oil consumption and emissions.

AMSOIL Now An ISO Certified Manufacturer
AMSOIL recently received ISO 9001:2000 certification of our Quality Management System (QMS). NSF International Strategic Registrations is the registrar that has verified our QMS meets the requirements of the ISO 9001:2000 standard, the most widely utilized quality standard throughout the world for quality management systems. ISO standards are used by over 300,000 companies worldwide setting rigorous standards for businesses, government and industry.

ISO 9001:2000 is applicable to any manufacturing and service organization providing a framework for system development that focuses on the customer, quality system performance and ongoing improvement. AMSOIL received ISO 9001:2000 registration under the scope: synthetic lubricants blending, packaging, and other fulfillment directly associated with lubricant product.

The ISO certification puts AMSOIL in line with some of the most efficient companies in the world. It is further assurance that the products and services AMSOIL provides will continue to maintain the high level of quality the company always demanded.

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