PNEUMATICS Chapter 5 Secondary Air Treatment RBTC-1359-01

Objectives Chapter 5 SECONDARY AIR TREATMENT Methods of Air Treatment Contaminant Separation Contaminant Filtration Filter Classification Media Types Surface Filters Mesh Particle Size Depth Filters Dry Filters Wetted Filters Oil bath filters Adsorption Filters Absorption Filters Lubricating the Air Heavy Lubricators Fine Lubricators

Introduction Chapter 5 Secondary Air Treatment Definition: Primary Treatment (Chapter 4) = Cleaning or filtering air as it enters a compressor. Secondary Air Treatment (Chapter 5) = Removing any contaminants that were carried over through the first part of the system

Methods of Air Treatment 5.01 Air is drawn from various surroundings will sometimes remain in the air through the first stages of compressing These contaminants are in the form of smoke, dust or dirt or lubricating oil picked up from the cylinder walls Remaining moisture contributes to rust and corrosion Secondary treatment is accomplished through : ABSORPTION ADSORPTION

Contaminant Separation 5.03 Separation of contaminants is accomplished by: GRAVITY SEPARATION CENTRIFUGAL SEPARATION INERTIAL SEPARATION

GRAVITY SEPARATION 5.03 Accomplished by rapid deceleration Separators Scrubbers Filters Receivers This Gravity Separation takes time and only removes the larger particles from air

Gravity and Centrifugal Separators

Centrifugal Separation 5.04 Cyclone or Centrifugal or Inertial separators use centrifugal force to throw solid and liquid (heavier) particles to the outside. These units are best fitted for high volume aps Commonly on intakes for centrifugal compressors Inertial separators (Impingement Separators) depend on changing direction in a hurry using dispersion plates to allow heavier particles to impinge on the plates or baffles

Contaminant Filtration Particle size – micron = 0.001 mm or 0.00004 inches 0.01 to 1.0 μ = smoke 0.01 to 0.8 μ = oil particles – aerosols 0.1 to 10 μ = cloud particles > 10 μ = dust

Filter Classification 5.11 Two Basic SOLIDS type filters SURFACE – regular pattern – narrow range but removes smaller particles as contaminants buildup DEPTH – irregular pattern – large openings up front scaling to smaller openings at back Common to use both Nominal Rating – a filter is classified by the percentage of particles of a given size that it can stop Absolute Rating - It stops 100% of a given particle size All are rated by airflow rates

Classifying continued Dirt Capacity = amount, size, type and concentration Multiple filters should be used to remove specific amounts and sizes of contaminants MAXIMUM ALLOWABLE PRESSURE DROP

Migration – 5.15 Contaminant Migration refers to an excess situation where the filter allows the collected particles to pass through Abrasion Migration refers to particles passing around the seals of the filter in the housing Medium Migration refers to the breakdown point of the filter itself – this allows for CONTAMINANT RELEASE

Types of Media 5.19 SURFACE FILTERS: Strainers – metal cloth, disks, screens Sintered metal powders Thin, felted fibers Thin membranes Woven cloth

Media DEPTH FILTER MEDIA: Felted or matted nonmetallic fibers Packed fibers Oil bath Activated carbon and other dessicants papers

SURFACE FILTERS/STRAINERS 5.21 SS - Wire mesh in pneumatic systems Catch larger particles SS Wire Mesh refers to size of opening Limited by the size of particles they can remove Two types of weave: Square Weave – for use where air is clean Dutch Twill – better for air ‘cuz openings are smaller

Wire Mesh – 5.21

Strainer Cross Section

Strainer and Strainer Baskets

Strainer Loop

Bag Filter Housing and Bags

Cartridge Filter and Cartridges

Pleated Cartridges

Ribbon Filter Pet Supplies for clean water

Mesh Relation MESH PARTICLE SIZE µ = micron 325 30 µ (0.0012 inches)

Depth Filters 5.25 Matted and or packed type filters Two Types – either Dry or Wetted or Oil Bath Commonly used for Compressor intake to stop large particles To collect moisture, oil and solids Just prior to end use of air 1) Dry Filters depend on the medium – don’t back wash 2) Wetted Filters depend on a coating of oil – can be cleaned repeatedly

Oil Bath 5.28 3) A version of a “wetted” filter Benefits include: Large volumes Remove 100% of particles 3 μ and larger Easy to clean For intake of lubricated reciprocal compressor

Filter Requirements 5.29 Intake for lubricated Reciprocating Compressors Require 100% of > 10 µ Un-lubricated Compressors Require removal 100% of > 5 µ Dynamic Compressors Require removal 100% of < 5 µ to protect impellers

Other Filters 5.30 Metal Powder – bronze (sometimes SS) for corrosion resistance Surface Filter Removal down to 2 µ possible Remove 90% of free moisture 5.32 Felted Fibers – masses of fibers matted together 5.33 Unfelted Cotton 5.34 Filter papers

Adsorption Filters 5.36 Vapor coalesces on the media – the drops settle to bottom Use carbon or powdered chemicals Same as desiccant dehydrators Difficult to regenerate Use replaceable media

Absorption Filters 5.38 Chemical reaction with vapor Commonly changes color to indicate replacement

Lubricating the compressed air 5.39 Common to need lube added to compressed air to reduce wear and corrosion Some pneumatic components require perfectly dry air Two types – Heavy or Fine Lubricators

Heavy and Fine Lubricators HEAVY LUBRICATORS 5.41 Supply fine suspended oil mist and heavy droplets Can use a wick type supplier Can use a venturi pick-up 5.44 FINE LUBRICATORS 5.45 Add a fine suspended oil mist into air Used for multiple equipment systems