1. Basic compressor knowledge

2. Effective  Absolute pressure
atmospheric
pressure
absolute
effective
total pressure
pressure = 0

3. Effective pressure
The effective pressure is the difference between absolute pressure and atmospheric pressure
It is the pressure available to deliver work
Absolute pressure
8 bar (118 psi)
Atmospheric pressure
1 bar (15 psi)
Effective pressure
7 bar (103 psi)

4. Effective pressure
XRVS 455 Md : receiver pressure during unload is 27 bar (397 psi)
Forces on the air receiver cover (0.08 m²) is more then 22,000 kgf (about 48k pounds)

5. Free Air Delivery
Free Air Delivery : is the measured “real” delivered volume of air (in l/s or m³/min or cfm) at the same conditions of pressure and temperature at the air inlet

6. Free Air Delivery
FAD is not equal to the displacement volume of the compressor element, because internal losses in the element (leaks to air inlet)
FAD is independent from the ambient conditions (temperature & pressure)

7. Screw Compressor Introduced in 1958 by Atlas Copco
Male and female rotors move towards each other, while the volume between them and the housing decreases.

8. Screw Compressor Screw profile improved in 1966
Symmetrical screw was changed to an asymmetrical helical profile
10% more efficiency

9. Compression principle
Suction
Compression start
Delivery
Compression

10. Pressure Ratio
Each screw element has a fixed, integrated pressure ratio
This depends on :
length of the rotors
Pitch of the screw
form of the discharge port
Best efficiency is reached when the pressure ratio is adapted to the required working pressure

11. Screw Compressor Design Advantages
High shaft speeds and large flow rate :
gives small exterior dimensions
Simple and strong design :
no valves and seals  reliable and maintenance friendly
small dirt particles improve the sealing and the efficiency
almost pulsation free air

12. Screw Compressor Design Advantages
Low wear :
guaranteed long life time and constant capacity
life time is determined by the bearing wear
Absolute oil free design possible
No inertia forces
vibration free operation
high speeds possible
big power possible

13. Screw Compressor Design Disadvantages
Lower efficiency because of internal leaks
High quality bearings on the rotors required
rotor clearances are small
axial bearings needed
Noise level (high frequency)
High quality finishing of the rotors required
expansion of rotors through heat results in blocked elements

14. Oil injected screw compressors

15. Oil injected screw compressors
Oil is used for :
Cooling : compression heat is absorbed by the oil
Lubrication of rotors, bearings, gears
Sealing between rotors and rotor and housing
Corrosion protection of the internal metal parts

16. Oil injected screw compressors
Oil is injected in the bottom of the rotor housing, onto the
bearings and gears, and discharged with the compressed air

17. Oil injected screw compressors
Only one rotor is driven, this rotor then drives the other one :
old XAS 90 : female driven rotor
all other compressors : male driven rotor
When required a gear box or drive belt brings the compressor element to the correct speed

18. Compressor running condition
Four major running conditions :
NO-LOAD Machine started, minimal pressure build-up
LOAD Receiver tank pressurized and air consumption
UNLOAD Receiver tank pressurized, no air consumption
BLOW-DOWN Machine stopped, blow-off of air pressure

19. Air system
Air filter Compressor Element (AFCE) (with vacuator valve VV, Safety Cartridge SC and vacuum indicator VI)
Unloading Valve (UV)
Compressor Element (CE)
Temperature Switch (TS)
Check Valve (CV)
Air Receiver (AR)
Non Return Valve
Minimum Pressure Valve (MPV)
Air Outlet Valve (AOV)

20. Air filter Filtration of the inlet air in 3 stages :
centrifugal dust separation
paper filter element
safety cartridge (optional)
Vacuum indicator gives an indication when the pressure drop over the filter element is too high  filter element needs to be replaced

21. Air filter Centrifugal separation Air inlet Vacuum indicator
Filter element
Dust
to compressor element

22. Unloading valve
Opens and closes the air inlet to the compressor element.
Open position at load condition => Air consumption
Closed position at no load condition => No air consumption.
Control of the valve by regulating pressure.

23. Unloading valve Regulating pressure Air inlet Spring loaded Vent Hole
Integrated
blow-down valve
Valve

24. Unloading valve
LOAD
UNLOAD
Regulating pressure
Air inlet

25. Check valve
Check valve is integrated in the unloader for Series 6 compressors (XAS 185, 375, 400)
Closes when the compressor is stopped.
The air receiver is pressurized, which would result in a reverse air flow.  the check valve prevents this.

26. Receiver pressure return
Check valve
LOAD
BLOW-DOWN
Check valve
Receiver pressure return
after shut-down

27. Air receiver / Separator
Separator element
Centrifugal separation
Air outlet
Air/Oil

28. Minimum pressure valve / nozzle
Guarantees a minimum pressure in the oil separator (approx psi)
Minimum pressure is required to guarantee an continuous oil supply to the element.

29. Nozzle / Minimum pressure valve

30. Oil system Air receiver Oil cooler Oil filter
Oil stop valve (where used)
Compressor element
Oil separator
Scavenge line

31. Oil system (without TBV)

32. Oil System (with TBV)
The following slides explain how the regulating system of the XA(H)S works. They will give you an overview of the different parts and their function.

33. Air receiver
Pressure
Oil flow

34. Oil cooler
Cool Oil
Cooling air
Warm Oil

35. Oil filter
By-pass valve
Dirty Oil
Filtered Oil

36. Compressor element
Greasing to the bearings
Air inlet
Oil
Air/Oil

37. Oil separator Scavenge line Separator element Centrifugal separation
Air/Oil

38. Regulating system Regulating valve Unloading valve Speed regulator
Blow-down valve
Safety valve

39. Regulating system (XAS 185)
Regulating Valve
Safety Valve
Speed Regulator
Unloading Valve

40. Regulating valve Regulates the effective pressure in the air receiver
Provides regulating pressure to :
unloading valve => regulates the air inlet according the air requirements
speed regulator => regulates the engine speed to reduce fuel consumption

41. Regulating valve Adjusting receiver pressure
by changing spring tension
Spring loaded
Pressure gauge
to speed regulator
to unloading valve
Regulating pressure
Receiver pressure
to blow-down valve

42. Regulating valve
LOAD
UNLOAD

43. Speed regulator
Regulates the engine speed in relation to the required air flow
Load condition : maximum engine speed
Unload condition : minimum engine speed

44. Speed regulator Spring loaded Regulating pressure Vent Hole
Engine speed
- Min
- Max

45. Speed regulator
LOAD
UNLOAD

46. Blow-down valve
Blows off the air receiver pressure once the compressor has shut-down => this to depressurize the receiver tank
Integrated in the unloading valve

47. Blow-down valve Receiver pressure blow-down valve Air inlet
blow-off hole

48. Blow-down valve LOAD / UNLOAD BLOW-DOWN Receiver pressure Blow-off
Receiver pressure return
after shut-down

49. Safety valve
Blows off the air receiver pressure once this pressure raises above the design pressure.

50. Electrical system Battery voltage : 12 or 24 V Starting system
cuts-out starter motor when engine is running
avoids cranking when receiver tank is pressurized
Safety shut-downs
Instrument indications

51. Safety shut-downs Compressor : Engine : Emergency stop
Compressor element outlet temperature
Engine :
Coolant temperature
Coolant level
Oil pressure
Fuel level
Emergency stop

52. Air treatment options Aftercooler Water separator Fine filters PD / QD
Re-heater

53. Air treatment options

54. Aftercooler - Water separator
The aftercooler is a heat exchanger, which cools the hot compressed air to precipitate the water that otherwise would condensate in the air hose.
The outlet temperature is ambient + 7°C.
It is followed by a water separator that separate the condensate and drains it
Used for : sandblasting, fibre optic cable steering, pipe cleaning

55. Aftercooler - Water separator

56. Fine filters PD / QD PD filter will separate oil and solid particles.
QD filter or carbon filter will separate oil and water vapour.
Discharge air is instrument quality--nearly “oil free”.
Only ppm oil present in the air outlet

57. Fine filters PD / QD
QD filter
PD filter

58. Re-heater
The re-heater is a heat exchanger, which warms up the compressor outlet air to ambient + 60°C.
The water and oil will be vaporized resulting in hot and dry air, this avoids condensate problems.
XAS : engine oil warms up the compressed air.
XAS : compressor oil warms up the compressed air

59. Product nomination oil injected compressors
Engine supplier
C : Caterpillar
D : Deutz
G : Detroit Diesel
J : John Deere
K : Kubota
Y : Yanmar
Working principle
A : Single stage compressor
R : Two stage compressor
Product range
X : Oil injected
portable compressor
Silencing
: Un-silenced
S : Silenced
Prime mover
d : diesel engine
E : electric motor X A M S
750 C d
Working pressure
Single stage Two stage
: standard pressure bar/100psi bar/250psi
M : medium pressure bar/125psi
T : “ten” pressure bar/150psi
H : high pressure bar/175psi bar/295psi
V : very high pressure bar/200psi bar/365psi
Capacity (FAD)
Liter/sec CFM (US-version)

60. Contact Numbers Main Number Atlas Copco Technical Support
Option 3
Ed Kukfisz – Compressors – Supervisor
direct & mobile
Andrew Stevenson – Compressors: Low Pressure
direct & mobile
Andrew Calendar – Compressors: High Pressure
direct & mobile
Scott Ellinger – Compressors
direct & mobile
Robert Walsh – Generators – Supervisor
direct (mobile)
Will Hudson – Generators/Compressors
Ext & mobile
Brandon Hobbs – Hydraulic Attachments /Handheld Construction Tools – Supervisor
direct & mobile
Al Eckenfels – Hydraulic Attachments/Handheld Construction Tools

61. Committed to sustainable productivity.