Air Compressors are efficient devices that significantly contribute to most daily industrial processes. They are mechanical devices that work to compress air, reducing its volume and simultaneously causing a pressure increase. These devices are essential in providing power for various tools, the manufacturing industry processes and machinery. Their use could be on an individual basis as surface finishing air tools, or for providing energy generation for pneumatic power systems and automotive repair equipment.
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History of Air Compressors
During 1500 B.C, metalsmithing was at its peak, and the metalsmiths working with basic tools, realized that higher temperatures were needed to melt gold and copper. Air pressure was thus critical in sustaining the fire. Therefore, the demand for stronger compressed air had to be addressed, leading to the invention of the first type of compressor known as the bellows. It consisted of just leather bags for pumping air but was later modified by adding handles and intake valves which facilitated continuous operation.
In 1650 B.C a German scientist, known as Otto von Guericke designed the first air pump that had one piston and just one cylinder. George Medhurst of England developed a motorized compressor in 1799. More inventions happened whereby Isambard K. Brunel designed a caisson that worked through pressure force in 1852. Later, an Englishman by the name Thomas Cochrane designed a drill in 1857 that was used in tunneling. It worked on the principle of compressed air.
The inventions in air compression continued revolutionizing with time, up to what we have today. The success is much attributed to the named personalities.
Power and Operation for Air Compressors
Air Compressor Operations
The air compressor, through a wide range of suction processes, pulls in more and more air into a storage tank and as the air piles up within, its pressure ultimately increases. Once the tank has reached its limit, the compressor automatically shuts off. The air inside is held back until it’s called to use. It can be utilized in making use of its kinetic energy as it leaves the tank while it undergoes depressurization.
With the continued air escape, the tank reaches a low limit, and once more, the compressor automatically turns back on and sucks in air to pressurize the tank. Air compressors power is measured in CFM which means cubic feet per minute air intake. Pressure bar and power kw are some other essential measurements that help understand working of compressed air. Bar flow can be determined from the output velocity.
Air compressors mainly comprise of two components that are;
- The mechanism that compresses the air
- The power source for that mechanism
Powering the Compression Process
The compression process requires a lot of energy which can be acquired from devices such as an electric motor, a power takeoff or a gas-powered motor. Once the compression device is powered up, the compression mechanisms take effect and begin the compression. These mechanisms could be either impellers, pistons or vanes. The compressor, therefore, is able to pull in air, store it temporarily thus in the process converting mechanical energy into pneumatic energy.
In the design of air compressor parts, the manufacturers over the past have had a preference for natural gas-driven products. The reason is because natural gas is affordable and offers less energy consumption. Recently, quality air compressors have been modified for use as power sources which was not the case earlier.
The compressors were previously known for everyday purposes such as inflating, cleaning and surface finishing. In the meantime, automotive manufacturers are starting to embrace and experiment with the pneumatic energy that is produced by the air compressors as they relentlessly search for alternatives to internal combustion engines.
Through the compression and resultant pressure, air compressors can be further classified into compressors that operate on low pressure, those that operate on medium pressure and finally, high pressure air compressors.
Positive and Dynamic Displacement Compressors
Industrial compressors effectiveness is made possible by some methods of compression which are grouped into two namely positive and dynamic displacement.
Compressors Operating on Positive Displacement
The positive displacement compressors operate by directing air inside a chamber. Then the chamber volume is reduced consistently, in result, compressing the air. When the chamber attains a maximum pressure, it allows for a valve to open up to discharge the air to the outlet system which is located outside the compression chamber.
They are then specified according to:
- Compression levels
- Technique used to cool down (oil, air, water)
- Powering technique (steam, motor or engine)
- Method of lubrication (oil, oil-free)
Rotary Screw Compressors
These fall in the positive displacement compressor category. The compressors are made up of two rotors that are enclosed, working to compress the air. Worth noting is the absence of valves. The units are also cooled either by air or water. For these types of compressors, the cooling is designed to take place on the inside of the compressor. Thus, all the working parts are neither exposed to or experience the extreme temperatures resulting from the operation. Therefore, the rotary compressor works continuously either as water or air cooled.
An advantage of the screw air compressor is that it offers simplicity in operation and maintenance. More so, the capacity control for these devices is attained through variation in speed and compressor displacement variation. To achieve the compressor displacement, there is slide valve integration that is strategically placed. With a reduction in compression, it triggers opening of the slide valve, ejecting the air.
Oil-free rotary air compressor uses air nozzles to aid in compression of the air, while ensuring that the oil inside the compression chamber does not yield actual air that doesn’t include oil. The oil-free rotary screw compressor could either be water cooled or air cooled, providing similar flexibility as oil flooded rotaries.
Reciprocating Air Compressors
These are a type of displacement compressors. Meaning that, in order to increase air pressure, they reduce its volume. The process can be explained that the compressor takes in air, confines it in an enclosure and then increases its pressure. This is accomplished through a piston which primarily operates as a compressing and displacing element.
Some of the commercially available reciprocating compressors are;
- The Single stage compressors
- The Two-stage compressors
- Single stage compressors work for the pressure bar of 70 to 100 psi while the Two-Stage compressors deal in higher pressure of 100 to 250 psi.
In the reciprocating compressor, it is said to be single-acting in instances where the compression makes use of one piston side. When the compressor incorporates two piston sides during compression, it’s termed as double acting.
For reciprocating compressors, reducing the load is essential and attained through unloading the operating cylinders. This is performed conveniently through pushing the compressed air to the cylinder or by passing the air outside or within the compressor. More so, capacity control is attained through speed variation in gadgets that rely on engine power by controlling the flow of fuel to the engine. Also, reciprocating compressors could either be water cooled or air cooled in both lubricated or unlubricated modes.
Dynamic Displacement Compressors
In dynamic displacement similarly, kinetic energy is converted to pressure. The main industrial compressors in this category are centrifugal compressors.
The Centrifugal Compressors fall under dynamic compressors whereby they are reliant on the energy transfer that is acquired from a rotating impeller and transfers it to the air. They therefore produce a high amount of pressure through converting the momentum energy from the rotating impeller.
For this reason, centrifugal compressors are designed to rotate at very high speeds in comparison to other compressors. Flow within the centrifugal compressors is in a continuous state. Thus, they are designed for larger capacity.
One of the conventional methods of controlling capacity is by regulating guide vanes. By closing the guide vanes, both capacity and volume decrease. They incorporate oil-free air compressor design.
Air Compressor Design
Air compressors appear in many varied styles. The reciprocating air compressors mainly perform the compression through the use of pistons that ultimately provide notable output capabilities. More so, they are cost friendly. On the rotary screw air compressors, their configuration is based on conventional, lubricated air compressors that bare the design of oil less air compressor. Last but not least, the centrifugal compressors are designed to operate in an oil-free manner.
Design of air compressors by far determines the purpose to be served by each type of compressor. Rotary screw and the reciprocating air compressors can be produced with similar designs as the portable air compressors. Stationary air compressors may have limited portability, but they produce more power in a fast and efficient manner.
Oil-free compressor design has been taken into use by another type of model which is the rotary air compressor. The rotary air compressors are available in different sizes.
Air compressors could either be powered by a gas motor or electricity. Electric air compressors are designed with a power cord, and the 12- volt air compressor is always equipped with 12- voltage batteries which can quickly be recharged in a car cigarette lighter or through an electrical outlet. When a buyer intends to acquire an air compressor, he or she has the option of getting a new or a used one at their disposal. A used compressor could be appropriately maintained and in excellent shape, in the long haul, saving you a notable amount and yet it’s able to deliver outstandingly as a complete package.
Air Compressor Usage
- Inflation of tires, surface finishing and cleaning of parts in the automotive industry.
- Gas pumps application
- Power tools similarly make use of air compressors to deliver their functionality efficiently. These tools include chipping hammers, needle scalers, jackhammers, triggers/winches and air chisels. Other essential tools that utilize air compressors are spray guns, nail guns, drills and sanders. Sandblastersalso make use of air compressors
- Furthermore, air compressors are essential in providing air that is used in air purification systems, blast forges, airlock systems and not forgetting the temperature control systems.
- Air compressors are also widely used in filling metal oxygen cylinders that are used for deep sea diving.
Air compressors are made from 3 metals which are;
It’s worth noting that in circumstances where lightweight air compressors are needed, like in the portable or mini compressors, plastics are preferably used.
Compressor Upkeep and Maintenance
To ensure that the air compressors are in best and fit conditions with no possible leaks, it is therefore imperative to undertake routine maintenance which could entail replacing compressor fittings and maintenance. Some other check-ups that are recommended on daily basis for any compressors are;
Things to Consider When Purchasing a Compressor
Always make sure the operating temperature is verified to avoid overheating the unit
Checking of the differential pressure in the compressed air filter
Inspect for any oil or air leaks
Finally, make a judgement if the oil in the compressor needs to be replaced or not
There are numerous manufacturers who would be delighted to sell you air compressors. However, before settling for a particular company, it is paramount to put some factors into consideration. These include;
- How long has the company been in business?
- Are they the actual manufacturer or just resellers?
- Do they have a good reputation in air compressor manufacturing?
- What material do they use in the manufacturing?
- Do they have the right distribution network?
If these questions are satisfactorily answered, then they should out rightly steer you in making the most suitable judgement about the company on efficiently addressing your needs.
Summary on Air Compressors
Air compressors are modern marvels which have made fundamental contributions to the daily industry manufacturing procedures. Ranging from small and simple air compressors to the more complex in design, they all aim at efficiently simplifying daily operations. And for this reason, air compressors usage will continue into the foreseeable future.
Air Compressor Types
12 Volt Air Compressors
12 volt air compressors are machines that require 12 volts of power to reduce the volume of air in a tank in order to increase the pressure.
Axial compressors have flow in the axial direction by accelerating air tangentially with blades attached to the rotors. This increases the kinetic energy of the air and diffuses it through static vanes to increase its pressure.
Centrifugal compressors act on air with blades on a rotating impeller. The rotary motion of the air causes an outward velocity from the centrifugal force, and then a diffuser transforms this outward velocity into pressure.
Compressors are mechanisms used for compressing air to higher than atmospheric levels.
Diaphragm compressors achieve compression with the use of a flexing diaphragm that moves back and forth in a closed chamber; the design is an alteration of the reciprocating piston concept. The motion of the connecting rod under the diaphragm causes the flexing and only a short stroke is needed to generate similar pressure effects as those of a reciprocating piston compressor.
Double Acting Compressors
Double acting compressors use both sides of the piston to compress the air, both the forward and the backstroke.
Ejector compressors use a high-pressure jet stream. The drive of the stream is transferred to the low pressure of the air.
Electric Air Compressors
Electric air compressors are machines that use electrical power to pressurize air before releasing it in a high energy form.
Free Piston Compressors
Free piston compressors have an adjustable compression piston that moves along the length of a steel cylinder column. The guiding and compression pistons collide at the return stroke because the compressed air pushes back the compression piston in the last stage.
Gas Air Compressors
Gas air compressors are gas-fueled machines that reduce the volume of air in order to use the pressurized air for power.
Industrial Air Compressors
Industrial air compressors are mechanical devices used for industrial purposes that provide air at higher than atmospheric pressure.
Labyrinth compressors are oil-free and work without piston rings. A series of labyrinths creates the seal between the cylinder wall and the piston.
Liquid Ring Compressors
Liquid ring compressors have only one moving part, the impeller shaft assembly. The service liquid rotating in its casing forms the liquid ring seal, and air enters through the suction port, moves between the impeller blades and is compressed before discharging.
Lobe compressors use two mating lobes on different shafts that rotate in opposite directions to capture incoming air and compress it against the casing. Lobe compressors supply very high flows at pressure ranges between non-positive displacement compressors and other types of positive displacement units.
Mini Air Compressors
Mini air compressors are machines that reduce the volume of air in order to pressurize it and convert mechanical energy into pneumatic power. The pressurized air can then be used for a variety of applications; due to the limited size of mini air compressors, however, the output is small and limited to 250 pounds per square inch (PSI).
Non-positive Displacement Compressors
Non-positive displacement compressors depend on motion to transfer energy from the compressor rotor to the air. Initial acceleration of the air produces a negative (suction) pressure at the inlet port, which draws air in.
Oilless Air Compressors
Oilless air compressors provide air and power for various tools, machinery and manufacturing processes in industries that require clean air.
Portable Air Compressors
Portable air compressors are hand-held systems that do not require an electrical outlet.
Positive displacement compressors work by successively trapping a volume of air and reducing it, thereby increasing the pressure. The quantity of heat produced rises proportionally to the pressure rise, resulting in substantial temperature increases of the air and the compressor itself.
Reciprocating compressors move a piston to the top of a cylinder to create compression. These require either water or air cooled.
Rotary compressors reduce the volume of air by compressing it between intermeshing, counter-rotating components that force the air into a tank.
Screw compressors use two contra-rotating rotors that turn in a synchronous mesh. As air enters the sealed chamber, the rotors revolve, reducing the volume of trapped air and sending it compressed through the discharge port at the designated pressure level.
Swash plate compressors move pistons parallel to the crankshaft, either by a cam or by a plate mounted axially on the shaft and inclined to it.
Used Air Compressors
Used air compressors are previously owned machines that reduce the volume of air in order to increase its pressure.
Vane compressors have an eccentrically mounted rotor that is the only moving part and rotates within the stator. As the rotor rotates, centrifugal force forces the vanes from their slots, forming compression cells, and this pumping action of the vanes sliding in and out moves the air from the inlet side of the compressor to the outlet side.
Air Compressor Terms
- The removal of heat when the compression process is complete.
- Air Pressure Regulator
- A component of an air compressor that allows the user to adjust the air pressure in the air line.
- A condition caused by a difference in pressure in which air will flow back into the distribution pipes rather than in the intended direction.
- The element that houses the rotor and related internal components of an air compressor. This includes the integral inlet and discharge connections.
- Collapse Pressure
- The lowest amount of differential pressure something is able to withstand without deformation.
- Compression/Pressure Ratio
- The ratio of the absolute inlet pressure to the absolute outlet pressure. Compression/pressure ratio typically applies to a single stage of compression but could also apply to a full multistage compressor.
- The piston compartment in an actuator or reciprocating compressor.
- Discharge Piping
- The piping between the aftercooler and the compressor and the air receiver and the cooler separator.
- A flange-mounted belt drive, motor or direct coupling between the engine or motor and the compressor.
- The operation of an air compressor at full speed, having a completely open inlet and discharge delivering upper limit airflow.
- Guide Vane
- An adjustable fixed part that directs the flow of air approaching the inlet of an impeller.
- The component of the rotating element of a dynamic compressor that gives energy to the flowing medium through centrifugal force. An impeller is comprised of blades that rotate with the shaft.
- Intank Check Valve
- A valve intended to stop air pressure and volume from slipping out of the compressor tank back into compressor heads when the compressor is not running.
- Heat Exchangers that eliminate heat produced during compression between the stages of a compressor.
- Load Factor
- The ratio of the maximum rated compressor load to the average compressor load within a certain period.
- Load/Unload Control
- A method of control that permits the compressor to run either at no load or at complete load at the same time that the driver remains at a constant speed. Load/unload control is an attempt to match air delivery to the demand.
- Maximum Pressure Rating
- The highest-pressure level recommended for a compressor.
- No Load
- When an air compressor is running at full RPM and is wide open, but no air is sent because the inlet is either closed off or modified and will not allow inlet air to be trapped.
- Noncooled Compressor Cylinders
- Compressor cylinders on a reciprocating compressor that run at low compression ratios and undergo little temperature change. These are used mainly in oil and gas field applications.
- Pressure Inlet
- The total pressure (static plus velocity) at the inlet flange of the compressor.
- Pressure Rise
- The difference between the intake pressure and the discharge pressure
- The reversal of flow in a dynamic compressor. Pumping/surge takes place when the handled capacity is reduced to an insufficient pressure in order to maintain flow.
- A revolving element of a compressor. It consists of the impeller and shaft and may have shaft sleeves and a thrust balancing device.
- The part that the rotating elements are attached to and through which energy is transferred from the prime mover.
- Shaft Sleeves
- Mechanisms used to position the impeller or to shield the shaft.
- Sole Plate
- The pad the compressor is mounted on. This is implanted in concrete and usually metallic.
- Stack Up
- The interaction between the stages of a centrifugal compressor. In the design of a multi-stage compressor, every stage can only run at one point of its characteristic curve, and the determination of this point is done through the design conditions of temperature, flow and pressure.
- Surge Limit
- The capacity in a dynamic compressor under which the process becomes unsteady.
- Thrust Balancing Device
- Part of a revolving element that offsets the thrust of compressor impellers.