product design specification on air compressors
TRANSCRIPT
[]
2011
University of Hull
Ali Dostan
Air compressors
ContentsContents of figures...................................................................................................................................4
Content of tables......................................................................................................................................5
1.1 Introduction........................................................................................................................................6
1.2 Background........................................................................................................................................7
2. Compressors production design specification.....................................................................................8
2.1 Introduction....................................................................................................................................8
2.2 Customer requirement........................................................................................................................8
Purposes...............................................................................................................................................8
2.3 operation............................................................................................................................................8
Performance.........................................................................................................................................8
Size.......................................................................................................................................................9
Weight..................................................................................................................................................9
Ergonomics..........................................................................................................................................9
Aesthetics...........................................................................................................................................10
Health and safety...............................................................................................................................10
Environment.......................................................................................................................................10
2.4 Life...................................................................................................................................................11
Life expectancy..................................................................................................................................11
Service life.........................................................................................................................................11
Disposal.............................................................................................................................................11
Shelf life.............................................................................................................................................11
Reliability...........................................................................................................................................11
Testing...............................................................................................................................................12
Environmental impact........................................................................................................................12
Maintenance.......................................................................................................................................12
2.5 Producer...........................................................................................................................................13
Production Volume............................................................................................................................13
Product quality...................................................................................................................................13
Product cost........................................................................................................................................13
Company............................................................................................................................................13
Material..............................................................................................................................................13
2.6 Society.............................................................................................................................................14
2
Standards............................................................................................................................................14
Regulation &......................................................................................................................................14
Law....................................................................................................................................................14
3. Productions description......................................................................................................................15
3.1 Reciprocating compressor............................................................................................................15
...........................................................................................................................................................15
Failures of reciprocating compressors:..............................................................................................16
3.2 Belt driven reciprocating compressor..........................................................................................17
3.3 Direct drive reciprocating compressors.......................................................................................18
3.4 Rotary screw compressors...........................................................................................................19
Failures of rotary screw compressor..................................................................................................19
3.5 Oil- injected screw rotary compressor.........................................................................................21
3.6 Oil-free screw rotary compressors...............................................................................................22
3.7 Scroll compressors.......................................................................................................................23
4. Comparison........................................................................................................................................24
5. Discussion..........................................................................................................................................25
6. Conclusion.........................................................................................................................................26
7. Appendix............................................................................................................................................27
7.1 Appendix (A):..............................................................................................................................27
8. Bibliography......................................................................................................................................28
3
Contents of figures
Figure 1....................................................................................................................................................6Figure 2..................................................................................................................................................15Figure 3..................................................................................................................................................15Figure 4..................................................................................................................................................17Figure 5..................................................................................................................................................17Figure 6..................................................................................................................................................18Figure 7..................................................................................................................................................18Figure 8..................................................................................................................................................18Figure 9..................................................................................................................................................19Figure 10................................................................................................................................................19Figure 11................................................................................................................................................21Figure 12................................................................................................................................................21Figure 13................................................................................................................................................22Figure 14................................................................................................................................................22Figure 15................................................................................................................................................23Figure 16................................................................................................................................................23Figure 17................................................................................................................................................23
4
Contents of tables
Table 1...................................................................................................................................................16Table 2...................................................................................................................................................17Table 3...................................................................................................................................................18Table 4...................................................................................................................................................19Table 5...................................................................................................................................................21Table 6...................................................................................................................................................22Table 7...................................................................................................................................................23Table 8...................................................................................................................................................24Table 9...................................................................................................................................................24
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1.1 Introduction
Air compressors are one of the key elements in the industries which used in a wide range of situations from gas stations to major manufacturing plants and more and more, air compressors are finding their way into home workshops, basements and garages. The common source of the compressors is air which is an expansive material and hazardous and risky when used at high pressure therefore, most applications are restricted to things requiring low pressure (10 bar or lower) but there are industrial uses for high pressure air up to 100 bar.
Compressors are usually classified as below:
The basic function of all of them is to suck in air from ambience and make air at pressures considerably higher. Typically a storage vessel is used with the compressor. The same principle is applied to the compression of other gasses.[1][3]
Compressors are branched into few more types by their basic principle of operation shown more specifically in [fig.1] and targeted types by this PDS are going to be specified in background part.
Figure 1
compressors types [2]
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operation principle
positive displacementdynemic
staging
single stagemulti stage
service
lubricatednone lubricated
1.2 Background
This PDS highlighting popular number of positive displacement compressors as specified below.
Positive-displacement type compressor works on simple principle of increasing pressure by reducing the volume.
Reciprocating compressors are the most widely used type worldwide, they work on the principles of a bicycle pump and are characterized by a flow output that remains nearly constant over a range of discharge pressures, and they have two types called direct drive and belt driven.
Rotary screw compressor work by trapping the air between two helical different shape but fit in each other screw that sucks the air in and discharge it in the tank, they also have two types called oil-free and oil-injected.
Rotary scroll compressors have spiral rotors in place of pistons and give a continuous pulsation free discharge.[3]
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8
2. Compressors production design specification
2.1 Introduction
No work on the design of a machine can begin unless a clear complete statement of what that machine needs to do is known.This production design specification on compressors aims to study the range of compressor common to industry, which the most popular ones are reciprocating, belt driven, direct drive, rotary screw, rotary lubricated, rotary none lubricated, scroll compressors.
2.2 Customer requirement
Purposes Compressors are intended to provide compressed air to power
pneumatic equipment.
Regarding to its volume is able to be used in standard duty processes,
and also heavy duty in industrial.
Should make as less as possible noise and vibration.
The air compressor should not be used to supply breathing air, unless
they are designed for surface supplied diving or scuba diving
cylinder.
2.3 operation
Performance It is important to install the compressor in a clean, well ventilated
area where the surrounding air temperature will not be more than
60°C.
A minimum clearance of 45 cm from wall and also clear access to the
drain shall be provided.
If compressor capacity is over 500 litres the compressor must be
bolted to a flat, even, concreted floor.
Some models are oil-free while others must be lubricated with oil.
Compressors are used to increase the pressure of air from the initial
conditions to the discharge conditions, compressors may used as
vacuum pumps.
It is important to ensure that the location of the compressor is as free
as possible from the pollutant such as rain dirt.[1]
Size WxDxH mmCompressor type
Range, from Range, to
Reciprocating compressor
100x70x85 1070x460x650
Belt driven compressor
150x60x95 1500x1100x900
Direct drive compressor
80x50x70 700x400x350
Rotary screw compressor
700X270X470 1220×620×800
Rotary oil-free compressor
800x550x450 1500x1400x1300
Rotary oil-injected
750x650x700 1600x1300x1200
scrollcompressor
420x150x270 2200x1350x1700
The numbers has been rounded up.[4]
Weight Kg
Compressor type
Range, from Range, to
Reciprocating compressor
90 160
Belt driven compressor
80 170
Direct drive compressor
50 110
Rotary screw compressor
120 250
Rotary oil-free compressor
110 260
Rotary oil-injected
130 250
scrollcompressor
90 140
The numbers has been rounded up.[5]
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Ergonomics Most Compressors up to 10 bar are semi- automatic and most compressors over 10 bar capacity are fully automatic.
Shall be designed in order to optimize human well-being and overall performance.
Be as simple as possible to control by operator. Should have rounded edges rather than spiky sharp edges.
Aesthetics Should constitute essential safety features such as valves that allow the release of air in instances when the pressure in the tank is too much.
Should have reasonable appearance.
Health and safety Compressors are rotating machinery and pressurised component that are potentially dangerous equipment if not operated and maintained correctly.
Certain compressors can generate high level of noise that can be harmful in a lengthy period therefore sufficient ear protector should be worn.
No attempt should be made to touch the machine whilst it is rotating
If severe vibration is observed, the cause of this should be immediately investigated
Environment The environment around the installation may need to be monitored in order to detect gas leaks etc.
Must resist corrosion in average 60% humidity up to the date of its warranty.
Must be able to operate in different weather conditions.
Should produce as less noise and vibration as possible.[3]
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2.4 Life
Life expectancy Directly depend on how frequently compressor used and
lubricated. Oil free type last approximately 9000 hours. Oil user types last approximately 15000 hours. [3]
Service life Presence of dust and other contaminate in the air can build up on
the components such as valve, rotor or vane such build-up can cause premature wear and reduce the compressor efficiency.
Regular lubrication is vital when necessary.
Water produced from atmosphere vapour should be drained weekly or when necessary in case of manual drain.
Disposal If compressor is not in usable or repairable condition as they
mostly made from either aluminium or cast iron can be recycled.
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Shelf life Compressors are kept free of oil during stock period. This means they are capable of being stored for quiet long time in
cool dry place. They need to be oil up if applicable, once they are in use.
Reliability Compressors are expected to work up to its maximum life
expectancy if had been inspected and service regularly.
Testing All compressors will be tested before they leave the factory for Market and should all meet the UKAS requirement.[Appendix A]
Compressors must be tested under Pressure Systems Safety Regulations 2000 (PSSR).[6]
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Environmental impact
Most air compressors can produce considerable amounts of oil-contaminated condensate which must be separated and collected, then properly disposed.
Oil contaminate must not be discharged into open drains or directly to land, because this material is harmful to the environment and Water Resources Act 1991.
Maintenance
Manual should be read, maintenance and safety requirements by
the manufacturer should be applied as follow.
Tank should be drained any time as necessary, bear in mind that
most compressors have manual drain valves.
Some models must be lubricated with oil while others are oil-free
designs.
Dust should be removed from exterior, and air filter should be
clean or replaced if necessary.
Valve gaskets should be replaced each time valves are removed from pump.
Belt should be replaced regularly or if neccessery.
Regular general safety inspection is necessary.
The product has 2 years warranty from the date of purchased, any
indirect or consequential loss or damage that may result from
defect or malfunction of the compressors is not covered by this
warranty.[8]
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2.5 Producer
Production Volume Economical, low priced compressors are produced by 50 units per day.
Specific functional, high-priced compressors are produced by 10 units per day.
Product quality Economical compressors are produce by forging which land
the finished product expenses at inexpensive cost. Specific function compressor has been produced at high
quality with more specified tolerances.
Product cost Sterling pound
Compressor type
Range, from Range, to
Belt driven compressor
£140 £25000
Direct drive compressor
£50 £600
Rotary screw compressor
£3000 £30000
Rotary oil-free compressor
£3800 £28000
Rotary oil-injected
£3500 £25000
scrollcompressor
£3900 £10000
Reciprocating compressor
£4000 £9000
The numbers has been rounded up[ 7 ]
Company The company based in United Kingdom however the parts are
mass produce and out soured in china and assembled in United Kingdom.
The company is capable of producing up to 150 economical and 50 specific functional if pre-ordered 6 month in advanced.
Material Compressors are mostly produced out of aluminium or cast
iron. Combination of aluminium and iron cast sleeves is also
available.
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2.6 Society
Standards Compressors must meet the British standard UKAS. Compressors must conform to relevant British standard such as
Pressure Systems Safety Regulations 2000 (PSSR). [8]
Regulation &
Law Must conform to international environmental protection regulation. Must comply with international The Occupational Health and
Safety.
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3. Productions description
3.1 Reciprocating compressorAlso called piston reciprocating compressor, works just like a combustion engine but in exactly the opposite function, basically it works by movement of a piston or set of pistons in one direction and then into opposite direction inside a cylinder, this function compresses the intake air , an example of reciprocating compressor shown in [fig.2].
Figure 2
A typical Reciprocating air compressor [7]
The compressed air is stored inside a vessel which has two set of intrinsic valves which take care of intake air and the exhaust [ fig.3], this type of compressors are branched into two type of belt driven and direct drive.
shows the location of valve and how they work relative to each other [9]
16
Figure 3
Reciprocating compressors
Advantage Disadvantage
Relatively cheap Quiet noisy
Simple maintenance High temperature of discharged compressed air
Achieve high pressure ratio Long installation time
Loss in capacity with operation
Table 1
Shows pros and cons of reciprocating compressors
Failures of reciprocating compressors:
Most common fault that occurs in reciprocating compressors is broken valve. Failure of valves can lead to broken piston. If compressor have multiple piston, during quiet short period all piston will fail because the
good one working harder than the others.[3]
17
3.2 Belt driven reciprocating compressor
Belt driven type reciprocating type usually has longer life than direct drive type, they use an electronic engine which connected to the belt by number of pulleys [fig.4], the transmission ratio of the compressor allows the pump to run at low speed, which guarantees optimal levels of efficiency, lubrication, cooling and therefore long life, this type of compressors are Ideal for use in Site Highly Portable and Robust Unit Easy to use, robust design makes them Reliable and durable.
As belt drive compressor- oil filled pump like a car engine, turns slower, less heat and friction equals longer life.[3]
Figure 4 Figure 5
typical pulley and belt with A/C engine [10] presents a typical belt driven compressor [10]
Reciprocating belt driven compressors
Advantage Disadvantage
Portable Quiet noisy
Longer life than direct drive Replacement parts and repairing cost is higher than direct drive part
Cheap maintenance compare direct drive Complex Repairing
Table 2
Shows pros and cons of Reciprocating belt driven compressors
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3.3 Direct drive reciprocating compressors
Direct drive compressors shown in [fig.6] are designed for semi-professional users, this type can be classified as one of the smallest type compressor available in the market, they are ideal for DIY usage, portability is one of the best features that highlights this product.
However they are not as reliable as belt driven types and the main reason for that is cost of repair, direct drive motor tend to be expensive where as belt driven can be cheaper repaired however sometimes could be more complex than direct drive to repair. Belt driven compressor has oil filled pump like a car engine, whereas direct drive has no oil in compressor, turns faster, more heat and friction equal shorter life but replacement parts are cheaper and easier to replace than an oil pump. [3][1]
Figure 6 Figure 7 Figure 8
direct drive compressor[11] typical direct drive motor [12] inside view of [fig.5] motor [12]
Reciprocating direct drive compressors
Advantage Disadvantage
Shorter life than belt driven type Quiet noisy
low-cost maintenance compare to piston reciprocating
Shorter life than belt driven type
Portable
Suitable for variety of usage
Table 3
Shows pros and cons of Reciprocating direct drive compressors
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3.4 Rotary screw compressors
Rotary screw compressor [fig.10] is another popular type, It uses two helical rotors screws [fig.9] to compress the air. The rotors have a very special shape and turn in opposite directions with very little clearance between them, air sucked in at one end gets trapped between the rotors, and pushed to the other side of the rotors.[3]
Figure 9 Figure 10
inside view of rotary screw compressor[13] typical screw rotary compressor[13]
Rotary Screw Compressors
Advantage Disadvantage
Low level of noise Relatively expensive
Ability to supply high level of compressed air High temperature of discharged compressed air
Relatively low end temperature of compressed air Complex design
Relatively expensive maintenance
Table 4
Shows pros and cons of Rotary screw compressors
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Failures of rotary screw compressor
The most common problem is oil in the compressed air which occurs when oil separator filters fail.
Since this compressors takes in a huge amount of water which normally contain water vapour and compress it into smaller volume, water will be produced this water usually drained using automatic drain, automatic system can fail quiet often.[3][1]
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There are two basic types of rotary screw compressors: oil-injected [fig.9] and oil-free [fig.11] the injected type is most common due its law price compare to the oil-free one.
3.5 Oil- injected screw rotary compressor
Oil-injected screw rotary compressor has same principle working as the oil-free types with slight difference, the oil is fed into where the two helical rotors are turning as it shown in [fig.11], causes very smooth and quiet operation compare to the oil-free types, however the compressed air is mixed with oil and needs purification, this mostly achieved by centrifugal force in rotating rotors and the remainder oil is separated by filters, this type compressors are only limited to continues operation and not suitable for discontinues operations.[1][3]
Figure 11 Figure 12
shows circulation of oil in the rotors[14] typical oil-injected screw rotary compressor[14]
Oil injected Rotary Screw Compressors
Advantage Disadvantage
Low level of noise Relatively expensive
High volume of air, steady flow More suitable for continues operations only
Low energy cost
Table 5
Shows pros and cons of Oil injected Rotary Screw Compressors
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3.6 Oil-free screw rotary compressors
Oil-free screw rotary compressors [fig.14] also have the same principle working the oil-injected type and the only distinction is they are none lubricated, to prevent high friction there is a slight clearance between to rotors[fig.13], however more noise produced in contrast with oil-injected ones as it expected, due to high friction oil-free types require two stage processes to achieve same pressure that oil-injected ones can accomplish in one stage.
Usually in stage one air compressed to about 3 to 5 bars and then stage two compresses the air to the end level mostly 7 bar, this makes the machine more complex therefore more expensive.
However under certain circumstances where having 100% oil free air is the target for instance chemical and food factories oil-free type is preferred to the oil injected type.[1][3]
Figure 13 Figure 14
oil-free screw rotary compressor, inside view[15] typical oil-free screw rotary compressor[16]
Oil injected Rotary Screw Compressors
Advantage Disadvantage
100% oil-free More expensive than oil-injected type
More noise than oil-injected types
Servicing and repairmen is more difficult than oil injected type.
Table 6
Shows pros and cons of Oil injected Rotary Screw Compressors
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3.7 Scroll compressor
Scroll compressors [fig.16], compress the air using two spiral parts which one is stationary, and the other one moves in slight eccentric circles inside the other spiral shown in [fig.15], air sucked in as it demonstrated in part 2 of [fig.15] and then transport into the centre of the spiral as it shown in parts 3-4-5 of [fig.15] and finally the compressed air discharged into the vessel to be used for later purposes.
This type of compressors are none lubricated, despite of being oil-free they have highly smooth operation and incredibly low level of noise, they have quiet low pressure ratio compare to the other positive-displacement compressors type therefore they are not suitable where high amount of compressed air needed but being none-lubricated makes them good choice for drinking water pumps, treatment facilities and laboratories.[1][3]
Figure 15 Figure 16 Figure 17
rotary scroll process[17] typical scroll compressor[18] inside view of scrollcmp[18]
scroll Compressors
Advantage Disadvantage
extremely low level of noise relatively expensive
Oil free Produce low pressure ratio
Servicing and repairmen is quiet complex
Table 7
Shows pros and cons of scroll Compressors
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4. Comparison
Reciprocating
Belt driven
Direct drive
Screw rotary
Oil-injected
Oil-free
scroll
Life expectancy 4 5 3 4 5 4 4
Efficiency 3 4 3 4 5 4 3
Reliability 4 5 5 4 5 4 5
Cost 5 4 5 3 3 2 3
service 3 4 5 3 4 3 3
Complexity 4 4 3 3 4 3 3
Level of noise 2 3 3 5 5 4 5
Portability 3 4 5 3 3 2 4
Level of compressed air ratio
5 4 3 5 5 4 2
Installation duration 2 4 4 3 3 3 4
Discharged air temperature
2 4 3 5 5 5 4
Final feedback 37 45 42 42 47 38 40
Table 8 Comparison table
Table 9 Comparison key
Excellent Very good Good Poor Very poor
5 4 3 2 1
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5. Discussion
Study, analysing and comparing selected number of positive displacement compressors in this report
attempted to clarify and highlight some useful features of compressors to help consumers to select the
most suitable compressors regarding to their point, this can be achieve more clearly by using
comparison part, page 21 using the final feedback, however this guideline could be neglected and
selection could be done regardless of efficiency and reliability where low level of noise, 100% oil-free
discharged air, portability and cost is the main issue.
In most cases especially for semi-professional consumers cost is the main issue and can’t be neglected
by the producer therefore company need to reduce the final cost of the product as low as possible to
keep the company on track, this could be achieved by importing the material from the main source
countries and even importing the ready made parts from country with low-priced labour than united
kingdom for instance China or India can land the final price of product at a lower cost, then the parts
could be assembled in house under united kingdom based company licence.
It has been proved due to lubrication circumstances explained more specifically in section (3.2) that
the lubricated types of compressors are more reliable and have longer life expectancy where as none
lubricated types have their own advantage and used in some specialised places such as food purposes
and also laboratories, however lubricated types makes less noise and possibly vibration which raise
their level in industry.
It has also been drawn to attention that the most important part in all compressors regardless of type
of the compressor which can’t be ignored is safety valve which realises excessive air in the tank
which simultaneously and automatically prevents compressors from compressing more air which
could be potentially dangerous and also lead to bursting the tank and following disaster.
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6. Conclusion
Taking all evidence into account PDS of compressors and its additional information in this report was
written to describe and justify the ability, advantages and draw backs of some popular selected
compressors under positive displacement principle of working to help consumers to select the suitable
compressors for their targeted purposes and also protect the company from malfunction of
compressors and its consequences.
27
7. Appendix
7.1 Appendix (A):
Ukas standard covers
ISO 17025 ISO 9001 ISO 17020 ISO 13485 ISO 14001 ISO/IEC 20000 ISO 22000 ISO/IEC 27001/British Standard BS 7799 BS OHSAS 18001/OHSAS 18001 BS 25999
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Electric Pressure Washer, Gasoline Pressure Washer, Diesel Pressure Washer, Gun, Nozzle, Flange, Diesel Engine, Diesel Water Pump, Diesel Generator, Gasoline Engine, Gasoline Water Pump, Gasoline Generator, Gasoline Vibrating Spare - China Plunger Pump, Electric Pressure Washer, Gasoline Pressure Washer, Diesel Pressure Washer, Gun, Nozzle, Flange, Diesel Engine, Diesel Water Pump, Diesel Generator, Gasoline Engine, Gasoline Water Pump, Gasoline Generator, Gasoline Vibrating Spare Manufacturer,Supplier - China Lutian Machinery Co.,Ltd.. N.p., n.d. Web. 30 Nov. 2011. <http://www.chinalutian.com/products/Plunger-Pump-Series/Axial-Pump-Series/Engine-Direct-Drive(3WZ-1600D).htm>.
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