Oil Free vs Oil Less vs Filtration with Lubricated Air Compressor

Compressors: Oil Free vs Lubricated with Filtration

There are distinct differences between “oil free”, “oil less” and oil lubricated compressed air with filtration. Often, the terms “oil free and “oil less” are used interchangeably because they both refer to compressors with no oil in the compression chamber. More specifically, “oil less” compressors have no oil anywhere in the running gear, crankcase or compression end. Typically “oil-less” compressors refer to reciprocating (piston style) units whereby the crank bearing and bushings are sealed and permanently lubricated, as are the wrist pin bearings. The valves consist of aluminum alloys (or stainless steel for enhanced life. Lubrication is achieved by Teflon similar material) composite rider and compression rings which expand as they wear. The advantage of oil less reciprocating technology is that this type of compressor is relatively efficient and produces totally oil free air. Additionally they are typically economical to purchase. Familiar manufacturers for this type of compressor include Quincy (QRD series) and Powerex (OT series). The size ranges from 1⁄2 HP to 30 HP. They are popular with laboratory, medical and pharmaceutical applications. The biggest drawbacks of the oil less reciprocating compressors are the higher maintenance requirements, vibration and noise issues.

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Customer Air Test Report

Date: March 9, 2006
Re: Hycomp Air Compressor Gas Analyses
Hycomp AN6-B31-CGMU-20/1.5D
Ser # 00080X-XXX


Four gas samples in Tedlar bags were delivered to the lab for analysis. The bags were identified as follows:

  1. Compressed Air, 03/07/06, 09:00, 238°F
  2. Compressed Air, 03/07/06, 09:00, 178°F
  3. Pre-Air, 03/07/06
  4. Compressed Air, 03/07/06, 1:25 p.m.

The sample numbers on the left identify the samples throughout this report and the accompanying spreadsheet. The lab was asked to analyze the gas samples for hydrocarbons.

Infrared Gas Analysis

The gas samples were analyzed by infrared absorption spectroscopy. This method is capable of quantifying hydrocarbons at concentrations above about l part per million (ppm). The accompanying spreadsheet contains the results of this analysis. Most of the gases analyzed were not present at concentrations above the detection limits of the instrument. Carbon dioxide and water, which exist in”normal” air, were detected. Methane was quantified at 2 ppm, which is also typical of air.

This method is not capable of differentiating hydrocarbons with carbon chains longer than four. We could estimate that all four samples contained hydrocarbons with carbon chain lengths longer than four in the 1-2 ppm range. Because these hydrocarbons existed in the “pre-air” sample, there is no evidence that the compressors added these hydrocarbons to the air. Blank samples were measured to ensure the hydrocarbons did not originate from the instrumentation or the Tedlar bags. These tests proved that the hydrocarbons were present in the Hycomp background air.

Gas Chromatography – Mass Spectrometry (GC-MS) Tests

GC-MS tests were done to identify the compounds detected in the background air. Acetone and N,N-dimethyl acetamide (DMAC) were detected. I suspect these are used in some process in the plant or nearby. Most of the hydrocarbons detected were of carbon chain length 9-12.


Hydrocarbon levels of a few parts per million were detected in the gas samples. A few other compounds were also detected. No significant differences were seen in the samples, indicating that the various compounds detected were present in the background air.

Gas Test Report

Build Sheet

Sample Description

Air Compressor Gases

Lab Procedures

AP001,EP004,AP007 AP009,AP032,AP057

Date Received


Date Completed



FTIR DataLab Air1234
Carbon Monoxide<20<20<20<20<20
Carbon Dioxide413 443442502455
Nitric Oxide<3<3<3<3<3
Nitrogen Dioxide<2<2<2<2<2
Nitrous Oxide
Hydrogen Cyanide<3<3<3<3<3
C˲₄ Hydrocarbons<2<2<2<2<2
Hydrogen Chloride<2<2<2<2<2
Sulfur Dioxide<1<1<1<1<1


  1. Gas concentrations have units of ppm unless otherwise indicated.
  2. Water detected but not quantified.
  3. FTIR = Fourier Transform Infrared Spectroscopy.
  4. This report may not be reproduced except in full, without written approval from the lab.
  5. C˲₄ Hydrocarbons = Hydrocarbons having four or more carbon atoms.

Air Quality Chart


Oil Free Technology

Your process remains clean and your air stream pure because oil never enters the compression cylinder. When your process demands pure air, trust Hycomp.

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