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Basic compressor knowledge
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Effective Absolute pressure
atmospheric pressure absolute effective total pressure pressure = 0
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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)
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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)
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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
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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)
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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.
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Screw Compressor Screw profile improved in 1966
Symmetrical screw was changed to an asymmetrical helical profile 10% more efficiency
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Compression principle
Suction Compression start Delivery Compression
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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
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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
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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
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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
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Oil injected screw compressors
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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
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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
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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
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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
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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)
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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
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Air filter Centrifugal separation Air inlet Vacuum indicator
Filter element Dust to compressor element
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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.
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Unloading valve Regulating pressure Air inlet Spring loaded Vent Hole
Integrated blow-down valve Valve
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Unloading valve LOAD UNLOAD Regulating pressure Air inlet
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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.
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Receiver pressure return
Check valve LOAD BLOW-DOWN Check valve Receiver pressure return after shut-down
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Air receiver / Separator
Separator element Centrifugal separation Air outlet Air/Oil
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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.
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Nozzle / Minimum pressure valve
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Oil system Air receiver Oil cooler Oil filter
Oil stop valve (where used) Compressor element Oil separator Scavenge line
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Oil system (without TBV)
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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.
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Air receiver Pressure Oil flow
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Oil cooler Cool Oil Cooling air Warm Oil
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Oil filter By-pass valve Dirty Oil Filtered Oil
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Compressor element Greasing to the bearings Air inlet Oil Air/Oil
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Oil separator Scavenge line Separator element Centrifugal separation
Air/Oil
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Regulating system Regulating valve Unloading valve Speed regulator
Blow-down valve Safety valve
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Regulating system (XAS 185)
Regulating Valve Safety Valve Speed Regulator Unloading Valve
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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
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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
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Regulating valve LOAD UNLOAD
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Speed regulator Regulates the engine speed in relation to the required air flow Load condition : maximum engine speed Unload condition : minimum engine speed
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Speed regulator Spring loaded Regulating pressure Vent Hole
Engine speed - Min - Max
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Speed regulator LOAD UNLOAD
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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
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Blow-down valve Receiver pressure blow-down valve Air inlet
blow-off hole
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Blow-down valve LOAD / UNLOAD BLOW-DOWN Receiver pressure Blow-off
Receiver pressure return after shut-down
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Safety valve Blows off the air receiver pressure once this pressure raises above the design pressure.
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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
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Safety shut-downs Compressor : Engine : Emergency stop
Compressor element outlet temperature Engine : Coolant temperature Coolant level Oil pressure Fuel level Emergency stop
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Air treatment options Aftercooler Water separator Fine filters PD / QD
Re-heater
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Air treatment options
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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
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Aftercooler - Water separator
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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
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Fine filters PD / QD QD filter PD filter
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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
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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)
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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
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Committed to sustainable productivity.
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