Views: 78 Author: Site Editor Publish Time: 2026-10-12 Origin: Site
Since the launch of ISO oil-free certification standards, many misleading statements have circulated in the compressed air industry. One of the most widespread misconceptions is that an oil-injected air compressor fitted with premium filters can be classified as oil-free. Some suppliers even claim that oil-lubricated compressors equipped with filters produce cleaner air than genuine oil-free equipment. While inline filters can reduce oil particle levels, they cannot completely eliminate the risk of oil carryover and contamination. Purchasing temporary compressed air systems based on this flawed reasoning may lead to unexpected damage to sensitive production processes, finished products and the surrounding environment.
Air purity acts as a decisive factor for countless industrial applications. Even trace oil droplets or oil vapor mixed into compressed air can degrade finished goods, trigger costly product recalls, damage production machinery and bring about environmental risks. Your unique production requirements determine which air compressor fits your plant conditions best. The engineering team at Shanghai Rocky Machinery Co., Ltd offers technical consultation and equipment selection recommendations for full oil-free and oil-injected compressed air solutions.
Oil-free air compressors are not inherently superior to oil-injected models in every scenario. Equipment selection depends on process requirements and target compressed air quality. For applications with severe consequences from oil contamination, such as pharmaceutical processes, food & beverage production and air curtain systems, Class 0 oil-free air compressors are mandatory. For ordinary workshops and general manufacturing lines where oil contamination will not cause catastrophic losses, oil-injected air compressors remain a cost-effective and practical option.
Let us clarify frequently confused core concepts found in sales materials. “Oil-free” describes the structural design of a compressor: no lubricant is added inside the compression chamber. In contrast, Class 0 and “technically oil-free” refer to the purity grade of compressed air discharged from the unit. Although these terms are related, there are essential differences between them:
Deliver 100% oil-free compressed air. Despite higher upfront investment, these units represent the safest and cleanest choice for sensitive processes, ensuring no machine-generated contaminants enter finished products.
Such systems remain exposed to oil leakage risks. Essentially, they are oil-lubricated compressors paired with oil removal filters. Unlike genuine Class 0 oil-free compressors, these filtered systems only meet ISO Class 1 standards.
The International Organization for Standardization develops global specifications for commercial and industrial equipment, and compressed air has its independent ISO purity framework. Compressor systems are rated ISO Class 0 to Class 5 according to particle quantity and particle size in outlet air.
The original compressed air purity standard issued in 1991 was drafted by filter manufacturers to promote filtration equipment. It defined five oil concentration grades, with Class 1 as the highest tier. The Class 1 standard specifies an oil concentration limit of 0.01 mg/m³ under operating conditions of 1 bar(a), 14.5 psia and 20℃ (68℉). Systems meeting this threshold are often marketed by vendors as “technically oil-free” packages.
The standard was revised in 2001 and underwent a major update in 2010. The current version sets limits on total oil content (liquid oil, aerosols and oil vapor) and introduces dedicated testing protocols for oil vapor measurement. Class 0 was newly added to meet ultra-high purity requirements. Shanghai Rocky Machinery Co., Ltd supplies a full range of ISO 8573‑1 Class 0 certified oil-free screw, piston and scroll air compressors for food, pharmaceutical and high-purity gas applications.
All air compressors follow the same fundamental physical principle: when air is compressed, its volume decreases and pressure rises. Oil-free and oil-injected compressors share this core compression principle, yet oil-free units adopt special structures to avoid lubricant inside the compression chamber.
Synchronously counter-rotating screw rotors are driven by an external gear set. There is no direct contact or friction between rotors, so no lubricant is required in the compression chamber to guarantee oil-free compressed air output. Precision housing design minimizes pressure leakage and pressure drop flowing back from the discharge side to the air inlet. Restricted by temperature differences between inlet and outlet ports, oil-free screw compressors usually adopt multi-stage construction with interstage cooling to expand the available pressure range. Lubricating oil is used inside the driving gearbox; the “oil-free” label applies exclusively to the compression chamber. Outlet air only contains inherent impurities from ambient intake air, with no extra oil pollutants introduced by the machine.
It consists of crankshaft, connecting rod, piston, cylinder and valve assembly. The valve head on the top of the cylinder is fitted with intake and exhaust valves. Two thin metal valve plates are mounted on either side of the valve plate. When the piston moves downward, a vacuum forms above it. Atmospheric air pushes the intake valve open and fills the cylinder cavity. As the piston moves upward, trapped air gets compressed, closing the intake valve and opening the exhaust valve. Air flows into the air receiver tank. With every piston stroke, more air accumulates inside the tank and pressure rises steadily. Oil-free piston compressors do not inject oil into the compression chamber. Instead, PTFE-coated piston rings are used to reduce friction.
One orbiting scroll disc moves relative to a fixed scroll disc. As the two scroll profiles move against each other, the volume of enclosed air pockets gradually shrinks. The reduced cavity volume compresses intake air and increases gas pressure.
Oil-free compression technology eliminates the need for regular filter element replacement, as there is no compressor oil to capture. It cuts operating costs for oily condensate treatment and reduces energy loss caused by filter pressure drop. Oil-free air solutions also deliver notable environmental benefits: helping enterprises comply with global environmental regulations and protect ecosystems. System leakage and energy consumption are minimized, and condensate collection and disposal are no longer required.
Most importantly, manufacturers avoid the risk of oil contaminating product batches or disrupting production workflows, preventing brand reputation damage and profit losses.
Shanghai Rocky Machinery Co., Ltd provides flexible oil-free air compressor solutions. Whether you need temporary backup equipment for your existing production line or to build a complete permanent high-purity compressed air station, our Class 0 oil-free compressor portfolio includes water-injected oil-free screw air compressors, dry-type oil-free screw air compressors, oil-free scroll air compressors and oil-free screw blowers, as well as oil-free piston air compressors. These products are widely used across diverse industries.
Core features: Water serves as the sealing medium in the compression chamber; ISO Class 0 oil-free; better cost performance than dry-type oil-free compressors.
✅ Application industries: Food & beverage, pharmaceutical, packaging, electronics, laboratories, water treatment, fine chemicals and PET blow molding.
Core features: Two-stage compression; gear-synchronized non-contact rotors; high-standard Class 0 oil-free; high pressure resistance.
✅ Application industries: Pharmaceutical API, aseptic food processing, petrochemicals, lithium batteries, semiconductors, paper making and high-end powder coating.
Core features: Compact footprint, low noise, flexible start-stop; medium & small flow Class 0 oil-free.
✅ Application industries: Dental medical, laboratories, analytical instruments, small food equipment, precision electronics and small packaging machinery.
Core features: Large flow rate, low pressure and oil-free. It belongs to blowers (not air compressors, with low working pressure).
✅ Application industries: Wastewater aeration, biological fermentation, grain conveying, powder pneumatic conveying, environmental desulfurization and denitrification.
Core features: Simple structure, medium & small displacement, suitable for intermittent operation, economical price.
✅ Application industries: PET blow molding, small laboratories, medical devices, small food processing, auto repair, printing and small packaging equipment.
All of them can stably deliver oil-free compressed air for your sensitive production processes.
Are you searching for a Class 0 oil-free compressed air solution tailored to your process? Not sure which oil-free compressor matches your production workflow? Shanghai Rocky Machinery Co., Ltd offers a full product line including water-injected oil-free screw compressors, dry-type oil-free screw compressors, oil-free scroll compressors, oil-free screw blowers and oil-free piston compressors.
Please contact us and share your requirements for flow rate, pressure and target industry. We will provide professional technical proposals and customized quotations.
