Compressor Oils / 4 min
Compressor Oil Selection: The Right Oil for Screw and Reciprocating Compressors
In compressed air systems, compressor oils carry critical roles such as sealing and carrying away extreme heat. Failing to select an oil suited to the compressor type (screw or reciprocating) leads to clogged separators and carbon deposits (coking) at valves.
Published by: Rotek Technical Content Team
Content is published based on manufacturer technical documentation and equipment requirements as the basis for final selection. This is general guidance and does not replace equipment-specific manufacturer approval.
Review our editorial guidelinesTable of Contents
- - Oil Needs by Compressor Type
- - What Is the DIN 51506 VDL Standard?
- - Oxidation Stability and Deposits
- - Air-Oil Separation (Air Release)
Oil Needs by Compressor Type
In screw compressors, since oil is compressed together with air, excellent air-release properties and resistance to foaming are required (typically ISO VG 46 or 68). Reciprocating compressors reach higher discharge temperatures and need higher-viscosity oils (ISO VG 100 or 150) that don't form carbon deposits.
What Is the DIN 51506 VDL Standard?
The quality classification of air compressor oils is generally governed by the German DIN 51506 standard. The VDL class describes oils with very high oxidation resistance, designed for use in air compressors with discharge temperatures up to 220°C.
Oxidation Stability and Deposits
Every 10°C rise in temperature cuts a mineral oil's life in half. Low-quality compressor oils oxidize at high temperature, leaving varnish and carbon deposits behind. These deposits can cause valves to stick and pose overheating-related fire risks.
Air-Oil Separation (Air Release)
In screw compressors, the oil must separate from air quickly. Low-quality oils foam and escape into the air line, causing premature clogging of air/oil separators, increased oil consumption and contamination of pneumatic systems.
Frequently Asked Questions
Can engine oil be used in a compressor?
No, engine oil should not be used in compressors. Detergent additives in engine oils hold water (creating an emulsion) and foam, causing the compressor to carry oil into the air line and clogging separators.
Which viscosity should be chosen for a reciprocating compressor?
Reciprocating compressors generally operate at high heat and need a thicker oil film, so ISO VG 100 or ISO VG 150 is most often preferred, depending on ambient temperature.
Why does compressor oil run low?
If the compressor is constantly running at high temperature, the oil evaporates; if the wrong (foaming) oil type is used, or the separator is faulty, oil is pushed into the piping along with the air.
What does VDL class oil mean?
VDL refers to compressor oils under the DIN 51506 standard that can withstand air discharge temperatures up to 220°C, with extremely high resistance to oxidation and carbon deposits (coking).