1. PNEUMATICS Chapter 4 Primary Air Treatment
RBTC

2. Objectives Air Treatment Filtering Relative Humidity
Effects of Moisture
Water Removal
Dew Point
Moisture Separators

3. Objectives Continued Oil Scrubbers Air Dryers Air Receivers
Deliquescent
Adsorption
Air Receivers

4. Introduction Chapter 4
All air, gas, oil, water and any other fluids require treating or processing to make then suitable for the purpose intended

5. Air Treatment
Air is taken from various surroundings that make it unsuitable without treating or processing
All air has contaminants
All gas has variations
The conditions vary from day to day
Our job is to make the air suitable for our use
Accessories fit the situation

6. Filtering Prior to compressing air requires filtering
The filter removes most dirt and contaminants
They are classed as:
DRY – generally cartridges or socks
Cotton or wire
Generally washable (no gasoline)
WET –
Maze above oil
The maze traps any particles coming from the oil
Volume requirements dictate sizing

7. Relative Humidity The amount of moisture in the air
Dependent upon temperature and weather
RH = The amount in the air compared with the amount that it could hold
100% RH is saturated air
The higher the temp the more water vapor it can hold
TABLE 4-2 Page 45

8. RH Examples Room 10 x 10 x 10 = 1000 cu ft
Temperature – as heated can contain more
Can hold 1 pound (1 pint) of water at 66°F
At 88°F it can hold 2 pounds of water
Pressure – as increased can contain less
Dew Point is the temperature at which the water vapor condenses
Under heavy load the air will not reach DP
Instead the moisture remains in the air
Rapid pressure drop through equip causes DP

9. Effects of Moisture – Left off 9 28
Rust and corrosion – chem reaction
Tanks, lines, vessels
Even if it stays in vapor stage
Common to reach DP and drop out
Liquid “washes” out lube
Plug small passages
Damage equipment like paint sprayers

10. Effects of Moisture continued
Oil can cause blockage
Oil can pick up dirt and carry into system
Emulsions – won’t lubricate if emulsified
Hi T can cause sludge and acid
Acids corrode everything
Commonly oil exists in a mist
Easy to remove
Deteriorates hoses

11. Water Removal
Methods
Most common method – condensation
1) Condensation can be used for both water and oil – drop the temp with an aftercooler
2) Dryer

12. After Coolers Use either air or water Scrubbers follow coolers
Air cooled – more economical in equipment
Small and medium volumes – 1 or 2 stages
Fin Fan
Tube
Water cooled – more economical in operation
Best for high volumes and larger compressors
Water removes heat faster
Scrubbers follow coolers

13. Water Cooled Shell and tube – most common
The air or gas gives up its heat to the tubes then the water
Can work both ways
Most heat exchangers work on counterflow
Dependant upon volume, pres, temp

14. Dew Point As air cools it gives up water
Dry air has a lower DP than moist air
Low pressure air has a lower DP than hi P air
Air/Gas expands as it cools – can reach DP
Avoid the problem by removing the water before it expands
First cool it and scrub it
Refrigeration can be used TABLE 4-1 Page 49

15. Moisture Separators All moisture removed has to go somewhere Scrub it
Mechanical separation
Centrifugal force
Velocity reduction
Gravity
Removes about 95% of liquids
Floats and valves remove the liquid from seps

16. Oil Scrubbers Oil scrubbers ensure more water removal
Usually large but simple
Based on velocity drop
Passes through bed of steel wool and moisture sticks to the steel – eventually dropping off
Can be solvent washed when ΔP occurs

17. Air Dryers Pneumatic gauges, controls and sensors require very dry air
Two types are used
Absorption – Deliquescent – Chemical
Use a soluble dessicant or liquid
When the soluble dessicant dissolves it deliquesces
Gas enters bottom and rises
Adsorption – regenerative
Use a dry dessicant

18. ADSORPTION Moisture adheres to the dessicant Only held on the surface
Gas goes in top and usually out the bottom during dehydration cycle
Reversed during regeneration

19. Air Receivers Used for storage Usually under pressure
Volume needed determines size of receiver
Peak usage time determines size