An air compressor is a type of equipment used to compress the gas. Air compressors are similar in construction to water pumps. Most air compressors are reciprocating piston type, rotary vane or rotary screw. Centrifugal compressors are used for very large applications.
Classification of air compressors
1.according to the working principle, can be divided into three categories: volumetric, power (speed or turbine type), and thermal compressor.
2.According. The lubrication method can be divided into oil-free and oil-lubricated air compressors.
3.According to the performance, it can be divided into low noise, variable frequency and explosion-proof air compressors.
Characteristics of air compressor
The compressor is directly driven by the electric motor, which makes the crankshaft produce rotational movement and drives the connecting rod to make the piston produce reciprocating movement, causing the cylinder volume to change. Due to the pressure change in the cylinder, the air enters the cylinder through the air filter (muffler) through the air inlet valve. In the compression stroke, due to the reduction of cylinder volume, the compressed air enters the storage tank through the exhaust pipe and one-way valve (check valve) through the exhaust valve. It is automatically stopped by the pressure switch when the exhaust pressure reaches the rated pressure of 0.7MPa. When the tank pressure drops to 0.5 – 0.6MPa pressure switch is automatically connected to start
And the air compressor is to provide gas source power, is the core equipment of the pneumatic system, and electromechanical lead air source device in the main body; it is the original (usually an electric motor or diesel engine) mechanical energy into gas pressure energy device, is the compressed air pressure generation device.
The vacuum pump is a device or equipment that uses mechanical, physical, chemical or physical-chemical methods to pump the pumped container to obtain a vacuum. Generally speaking, a vacuum pump is a device that improves, generates and maintains a vacuum in a closed space by various methods.
Features of vacuum pump
(1) Large pumping speed in a wide range of pressure.
(2) The rotor has good geometric symmetry, so the vibration is small, and the operation is smooth. The gap between rotors and between rotors and casing, no lubrication, and small friction loss can greatly reduce the driving power so that a higher speed can be achieved.
(3) No need to use an oil seal and lubrication in the pump chamber, which can reduce the pollution of oil vapour in the vacuum system.
(4) No compression in the pump cavity, no exhaust valve. Simple and compact structure, insensitive to dust and water vapour in the pumped gas.
(5) relatively low compression and poor pumping effect on hydrogen gas.
(6) The rotor surface is a more complex shape than the curved column surface; processing and inspection are more difficult.
Classification of vacuum pumps
Classified by performance characteristics and usage
(1) Low vacuum pump
The vacuum pump with an ultimate pressure higher than 102Pa belongs to the low vacuum pump. The common low vacuum pumps are reciprocating vacuum pumps, rotary vacuum pumps, liquid ring vacuum pumps, jet vacuum pumps and adsorption vacuum pumps.
(2) Medium vacuum pump
The vacuum pump with the ultimate pressure of 102~-10-1Pa belongs to the medium vacuum pump. The common ones are Roots vacuum pumps, multi-stage jet vacuum pumps, multi-stage rotary mechanical vacuum pumps and high-speed rotary mechanical vacuum pumps.
(3) High vacuum pump
The vacuum pump with the ultimate pressure of 10-1~10-5Pa belongs to a high vacuum pump. The common high vacuum pumps include various diffusion pumps, molecular pumps, etc.
(4) Ultra-high vacuum pump
The vacuum pump with an ultimate pressure lower than 10-5Pa belongs to an ultra-high vacuum pump. The ultra-high vacuum pumps mainly include various ion pumps, low-temperature pumps and other pumps.
Classification according to working principle and structural characteristics
(1) Mechanical volumetric vacuum pump
The pumping effect is achieved by the mechanical movement to make the working volume of the pump chamber change periodically, which is the core type volumetric vacuum pump. This pump has reciprocating vacuum and rotary mechanical pumps (including rotary vane, screws, roots, liquid rings, etc.). In addition to the mechanical booster pump, these pumps can be used alone.
(2) Jet-type vacuum pump
There are no mechanical moving parts, and the vacuum is pumped mainly by the high-speed jet through the nozzle. Such pumps include water vapour jets, air jets, water jets, and various diffusion pumps. These pumps have a simple structure, reliable work, long life, are easy to maintain, and are commonly used.
The difference between pump and compressor operating parameters
Pumps and compressors, as two specialized units, have a wide range of characteristics. However, some of them can be distinguished as fundamental. These values determine the range of application of the equipment and are the basis for calculating and selecting the specific target equipment. Other characteristics are of secondary importance and depend more on basic values. Secondary characteristics also influence the machine’s design, operation and efficiency, but to a much lesser extent.
The primary parameters determine the operating conditions of the pump or compressor. A suitable unit can be found based on a limited set of parameters. The selection can be based on a single primary parameter or a set of parameters, as needed.
Differences between pumps and compressors in terms of components
Describing all the constructional differences between pumps and compressors is difficult because each machine has huge differences. Both are classified according to their operating principle, application, fluid type, etc.
The basic components of a pump usually include the casing or housing, impeller, worm gear, motor and shaft.
A compressor usually consists of a motor, tank, valve, drain, intake filter, etc.
Differences between pumps and compressors in applications
Pumps and compressors are among the most widely used machines in different industries, technical constructions, factories, large plants and almost every household.
The most common use of domestic pumps is in washing systems, which drain water from equipment in sewage systems. Automobiles, aircraft and ships also use pumps in cooling, oil and fuel applications.
Many industrial plants have pumps for various purposes, such as irrigation, mining, air conditioning, refrigeration, etc.
Compressors are commonly used in refrigeration technology (refrigerators, air conditioners and display cabinets). In addition, they are used in refineries, technical gas plants (O 2, N 2 bottles) and process industries such as pneumatic tools and automation equipment, including shipbuilding, construction, and vehicles (brakes and doors).
Differences between pumps and compressors in terms of physical changes in fluids
When a pump or compressor changes fluid energy, its physical properties may also change.
The fluid volume does not change from the inlet to the pump’s outlet. In addition, a pressure change does not necessarily occur.
It works based on the pressure change. Therefore, the gas volume will change.
Is it possible to use a vacuum pump as an air compressor?
We have already discussed the conversion of an air compressor vacuum pump. Therefore, you must be wondering if the reverse is also possible. Theoretically, this is possible but impractical. Therefore, you will not see much discussion on this matter. We have discussed the following reasons.
Air compressors have inlet and outlet ports. However, most vacuum pumps do not have any discharge ports or storage tanks. Therefore, it is difficult to store compressed air.
Compressed air may contain moisture and oil because the vacuum pump has no filtration system.
The vacuum pump vents the air to the atmosphere, so the output pressure is only 1 atmosphere. Air compressors can operate at pressures up to 100 psi, which is almost equivalent to 7 atmospheres. Therefore, a vacuum pump will not be able to meet the needs of an air compressor.
Although, some industrial-grade vacuum pumps may be powerful enough to be used as air compressors. Then there are various vacuum pumps, such as turbo-molecular and diffusion pumps, which cannot function as air compressors.
It can be concluded that using vacuum pumps as air compressors is neither feasible nor worthwhile.
There are still some differences between vacuum pumps and air compressors, so air compressors are not equal to vacuum pumps.
Using a vacuum pump: when negative pressure is needed, the vacuum needed is less than atmospheric pressure.
The use of air compressor: when the gas is transported in the pipeline, the air compressor will also be used, such as the transport of remote gas, bottling of various gases, etc.