Dry vs “Wet” Compressed Air

Basics

• This page aims to cover the differences between the Compressed Air as it comes out of most Air Compressors (particularly Oil Sealed/Lubricated Reciprocating Piston based compressors), and how that compares to properly filtered/“dry” air (and to a lesser extent Dry Nitrogen )
• The distinction is largely important for making sure it is compatible with the intended end use (or aiding in selecting Compressed Air Filters / Compressed Air Dryers etc), as well as for design of Compressed Air Plumbing for a Centralized System

Considerations

Preface

• As stated previously, this page aims to largely cover Oil Sealed/Lubricated Piston Based Compressors
• As the air exits most of these it contains Oil Mist and Water Vapor
• The Oil Mist isn’t the WORST for most things, but can be problematic for some uses, in particular Supplied Air Respirators etc
• The Water Vapor can introduce some issues in terms of Long Term Storage use, or especially later when it cools and forms condensate (which can lead to Vapor Lock / Steam Hammer type issues and other issues of a system intended to be Single Phase Flow becoming Two Phase Flow )

Oil Mist

• This is (for the most part) the easier to solve issue
• Compressed Air Oil Mist Filters are quite common
  • Demister / Mist Remover can be related terms for larger refinery sized units etc
• A Canister of Granulated Activated Carbon may be of use as well for “cleaning” any residual
• Finally for certain uses such as Supplied Air Respirators or SCUBA Tank Filling (or SCBA as well) verification of the Compressed Air’s cleanliness is also required