1、Concept and usage of air compressors
1）、Concept
Through energy conversion, transform 1 standard atmosphere into atmosphere with certain air discharging capacity and pressure.
Explanations: 1, 1 standard atmosphere. 2, Generally, energy conversion can be regarded as mechanical energy exchanged into motor energy.
2）、Usage
As one of an important energy production forms, air compressors are widely used in everywhere of the normal life and productive activities of the people. Especially the double-screw air compressors, it is widely used in the industries of Mechanic, Foodstuff, Pharmacy, Electronic, Textile, Automotive, and Architectural Material etc.. It has become the mainstream items in the fields of air compressors.
2、Parametric Units
A、Work Pressure of Air Compressors
A lot of representation forms are used for unit of pressure. Here, we main introduce the unit of pressure we usually used for screw compressors.
① Work Pressure, which we usually called exhaust steam pressure in domestic market. It refers to the highest pressure discharged by air compressors.
② The often used unit for pressure is bar or Mpa，1 bar equals to 0.1 Mpa.
③ Generally, it is called Kg by our users. 1 bar equals to 1 Kg.
B、Volume Flow
①Volume flow, which we usually called Air Discharging Capacity in domestic market. It refers to the amount of discharged volume per unit time convert to the flow-into under the required discharged pressure.
②Unit: Cubic per minute or litre per minute, 1 cubic equals to 1000 litre.
③General, common flow unit : m3 / min ( cubic meters / minute )
④Volume flow in our country is also known as the exhaust volume or nameplate flow.
C、 The Power of the compressor
①Generally, the power of the air compressor is the Nameplate Power of the matching driving motors or the diesel engine.
②Unit of Power: KW or HP, 1KW equals to about 1.333HP.
3、 Principles
1）、Process of air intake
The sidepods of the screw compressors must be designed to take in the air full. But it has no intake or discharging valves. A control valve’s open/close is the only way to take in the air. When the rotor is rotating, the space of the gear groove between the main and the subsidiary rotors reaches the maximum when they are rotating to the sidepod. And at this time, the space of the rotors communicates with the free air of the sidepod. It is because when discharging, the air of the gear groove has been exhaled, after discharging, the gear groove is in vacuum and when rotating to sidepod, the surrounding air is absorbed in and enters into the gear groove of the rotors. When the groove is full of air, the side face turns away from the sidepod, the air is closed. The above is the process of intake.
2）、Closing Process and Transportation Process
After having finished the intake of the two rotors, the face will be closed with the chassis. At this time the air is closed in the gear groove without flowing out. This is the Closing Process. The two are rotating continuously, the face meets with the groove at the intake side. The .anastomsis side is moving to the discharging side. That is the Transportation Process.
3）、Compression Process and Fuel Injection Process
During the transportation, the .anastomsis side is moving to the discharging side, that is, the gear groove between the .anastomsis side and the outlets, the air in the groove is compressed gradually. Then, the pressure is going up. This is the Compression Process. At the same time, ubricant oil is sprayed into the compression room and mixed with the air because of the difference of pressure.
4）、Discharging Process
When the .anastomsis side communicates with the outlet of the chassis, (At this time, the pressure is the highest), the compressing air is discharging till the anastomsis side moved to the outlet side. At this time, there is no space in the groove between the .anastomsis side and the outlet of the chassis. This is the Discharging Process. At this moment, the length of the groove between the anastomsis side and the outlet of the chassis is the longest. The process of air intake is again.
4、Basic structure of the Screw Compressors
Usually, what we called screw compressor refers to double-screw compressor.
In the host machine of the compressor, it is equipped with a couple of screw rotors. Usually, rotors with convex gear (from the cross section) outside the pitch are called male rotor or male screw. And rotors with concave gear inside the pitch (from the cross section), are called female rotor or female screw. Generally, as the active rotors, female rotors rotate with male rotors. Axial Positioning comes true because of the ball bearings on the rotors and expose the axial force in the compressor. The taper rollers on both sides of the rotor push the bearings and Variation Positioning comes true and exposes the axial and the variation force in the compressor. Orifices with certain shape and size are equipped on both sides of the host machine, one is used for air in take, which is called inlet, and another one is for discharging which is called outlet.
5、Features
1）、Originally imported from Germany, as the most advanced host machine in the world, the Gen 3 has excellent features with unsymmetrical involutes gear 5:6 rotors. The advantage of high efficiency is far superior to anything else of the kind.
2）、It has the following features: high efficiency, low noise, low vibration, convenient operation, easy to maintenance, long service time and to be controlled automatically.
3）、Automated control system, liquid-crystal display screen, Self-diagnosis and protection equipment, distance control and control of multiple associated hosts, unattended and distance operation.
4）、Intelligence auto-regulation, automatic startup and automatic power saving function stands, the saving is up to 25%.
5）、Series Y motor for compressor with SKF/FAG bearings, isolation Rate F, protection grade reaches IP54. It’s safety for long time operation.
6）、Both oil filter and oil-gas filter core are all imported from MANN Company, Germany. Triple oil-gas filter guarantee the oil content is less than 3ppm. Metal pipe is used for the authoritative, no leaking and no deformation even longtime operation.
7）、No valves in oil system, which makes it more reliable and more safety.
8）、Originally imported from Optibelt Company, Germany, the service time of the V transmission belt is more than 10000 hours.
9）、Because of the originally imported fittings for Oil System, Gas System and Electronic Control System, the machine has a stable performance and reliable quality, and can adapt to any bad working environment.
10）、Professional high efficiency lubricant oil has good antioxidation, water-separati-on and abrasion resistance properties, which greatly expands service time of the compressor’s oil, reduces leakage out/in side the compressor and improves the host’s efficiency and service time.
11）、Service times of air filter, oil filter and oil-gas filter are expanded greatly because of its quiet design and hermetic baseboards.
12）、The overall body is removable and convenient amending.
6、What is the usage of the smallest pressure valve?
1） It is for buffering. At the moment of loading, it will damage the separator because of the differential pressure before/after the separation if we discharge the air directly to the atmosphere.
2）Without extra help from pump, it depends on differential pressure of itself. Certain pressure is needed to maintain circulation at no-load state. So the intake valves are close relative. The lowest pressure valves prevent the leakage and guarantee lubricant circulation.
7、Why to deal with the compressed air?
There is a great deal of harmful impurities, such as dust, water and so on. Most of the impurities will enter into the air compressor and be discharged through compression except some big dust prevented by the filter. Also, the lubricant oil in the compressor is unable to be completely separated by the oil-gas separator, even no-oil compressor. After compression, the density of the oil in air has greatly increased, Water vapor in the compressed air is in the state of saturation, and liquid water will be out at anytime.
Output from the compressor, the compressed air has a lot of harmful impurities. Without cleaning these impurities with proper way, it will do great harm to the gas source system. Among these, oil is the most harmful. Deteriorated lubricant oil will cause deterioration for rubber, plastic and seal material, and plug up the small holes. And then, valves will be out of order and pollute the products.
Water and dust eat into metals and pumps, moving parts will be locked or worn, pneumatic element will be out of order and leaking. Small holes or filters will be plugged up. In cold region, pipes will be locked or froze and burst because of frozen.
Because of the bad air quality, reliability and service time of the pneumatic system reduces greatly, the loss caused by which is much more than gas treatment unit and the maintenance costs. So it is very necessary to properly choose gas treatment system.
Compressed air processing equipments includes the followings:
Water Separator: to get rid of liquid water.
Precision Filter: to get rid of liquid water, oil and dust.
Carbon Filter: to clear ill-smelling and harmful gas in the compressed air.
Dryer: to dry steam. It has to kinds, one is freezing dryer, and the other is absorbing dryer. Freezing dryer is suitable for the place where had a low requirement for the temperature. But absorbing dryer is the opposite.
8、Advantages of Frequency Conversion Compressors
High efficiency with little electricity is unbelievable.
With the technique of speed control, air Discharging Capacity fits nicely with gas requirements by the users, and avoids loss from unloading.
At the state of interrupted gas consumption, through no-load affection of the Soft Start-up is to avoid the peak of current and torque. The unit can start and stop indefinitely. 0 to 100 infinitely variable speed transmission becomes true and worthless power is controlled by the greatest extent.
Avoid 2bars extra pressure and save 14 percent energy directly. This is because reduces 1bar pressure, 7 percent energy can be saved.
Required pressure can be set free and kept steady.
At the range of 3 to 14 bars, pressure can be set free without exchanging gear or strap.
At the required pressure, the unit provides gas at constant pressure at the range of ±0.1bar.
When requirement for gas is increased, automatic compensation from speed will guaranteed it without changing the pressure.
When requirement for gas is decreased, speed will low down automatically but the pressure will keep the same.
Advanced Distance Control
Advanced controlling, monitor and communication System can provide technical assistance for users all over the world on the internet.
More reliable.
Electric shock and mechanical shock are avoided because of the frequency soft starter.
Avoid disadvantage of high-speed and long time operarion.
Without contactor and avoid failure by electric contact.
Avoid 2 extra bars pressure and decrease chance of leaking.
Energy-saving, Environmental Protection, Equipment is set and can be start at once.
Easily installed, no need basis. Low-speed Axial-Flow Fan and modern vibration isolation and noise abatement measures makes low noise in the operation, which makes it easier for users to place it on production scene. It can start immediately just equipment fixed and pipes connected.
Save energy and emission reduction , developing scientifically.
Frequency screw compressor
Price differentials with non-frequency compressor will be recovered in one year energy saving, total cost of the Frequency unit will be recovered in three years saving.
9、Basic Standards for selecting compressor
1）、The Exhaust Steam Pressure and Air Discharging Capacity should be considered first.
The Exhaust Steam Pressure for general application is 0.7MPa, which is 0.8MPa in former. At present, a compressor with 0.5MPa Exhaust Steam Pressure is in use, which is irrational from practical use. For wind-driver tools, they can not work if remaining pressure is too low or the gas transportation distance is too far. Besides, judging from the design, the first-class compression will cause high temperature, carbon deposit in the cylinder and then cause accident because of the high differential pressure. Compressors beyond 0.8MPa will be specially produced, but not force increase the pressure, which will cause accident.
Air Discharging Capacity is one of the important parameters; it should be matched with the air capacity of the compressor and with extra range from 10 percent to 20 percent. If the desired air capacity is larger than the air discharging capacity, after having been started, the wind-driver tools will be unable to work because of the greatly decreased discharging pressure. Of course, it is a mistake to blindly pursue large air discharging capacity. The larger the air discharging capacity, the bigger the matching motor will be. Not only the price is high, but also the fund of purchasing will be wasted, and so is the electrical energy.
Besides, the peak consumption, normal consumption and the lowest consumption should all be considered when selecting. If the amount for the lowest consumption is much higher than the normal and peak consumption, connecting in parallel of compressors of lower air discharging capacity is used to get a larger one. Start up one by one with the increase of the consumption, which will be good for the electrified barbed wire and save energy.
2）、Circumstance and Condition
Vertical compressors will be suitable for narrow circumstance (such as for marine or motor). If there is a long-distance (beyond 500m) change about the site, movable compressors will be better. If power supply is not available at the position, a diesel engine should be selected. If no water, air-cooled type is a must.
Air-cooled or water-cooled, users usually have a mistake recognition on which one to select, they believe the water-cooled is better. In fact, the air-cooled compressors take above 90 percent Home and Abroad. It is because air-cooled is simple in design, and water source is not necessary when use.
But the water-cooled types have four fatal disadvantages: one is that sound water in/out system is a necessity, which is a great investment. Second is the short service time. Third is that the cylinder is easy to be frozen and break in winter of south area. Finally, a large amount of water will be wasted.
3）、Compressed air quality should also be considered.
Compressed air by the compressor consists of a quantity of lubricant oil and a quantity of water. In some position, oil and water is prohibited. On this condition, type of the compressor should be careful. If necessary, attachment should be equipped also.
One solution is to select No-oil Lubricated Compressor. Basically, there is no oil in the cylinder of this kind of compressor. Generally, piston ring and fillings are PTFE. But this machine still has its disadvantage, which is bad lubrication and high breakdown rate. What’s more important is PTFE is a harmful substance, which is prohibited to be used in the fields of food and pharmacy. This kind of compressor can transmit gas without oil but not water. Another solution is the most commonly used method . That is to equip whatever kind of compressor with primary or secondary class cleaning system or dryer, which makes the air without oil and water. The rate of oil/water content is below 5ppm, which meets the requirements.
4）、Safety Operation should be considered also.
It is machine which works with pressure. Accompany with temperature rise and pressure, safety operation should be put in the first place. The state practices standardized two certification systems for the production of compressors. They are the compressor production license and the pressure vessel (gasholder) production license. So you should strictly examine the two licenses when you buy the compressors. Usually, manufactures with licenses have a complete quality management system, and big quality problems may not happen. Even if there is some, the factory will be responsible for it.
10.Difference between joint couplings and belt driving system.
With the widespread of air compressors in all industries, selection and maintenance of the compressors has been more and more important. It can be mainly divided into two kinds, one is joint couplings, and the other is the belt driving system. We will compare the two kinds in the following:
NO-loading Energy Consumption
No-loading pressure should be maintained beyond 2.5bar at the Gear Transmission. Sometimes, it will reach 4bars to guarantee the gear-box lubricated. For the Belt Driving System, no-loading pressure can be zero in theory. For the oil absorbed-in is enough to lubricate the rotors and bearings. For safety, pressure maintains at around 0.5bar. Take a 160kw gear transmission compressor for example, it works 8000 hours per year, 15 percent (that is 1200hours) time is in no-loading. This machine will draw 28800kwh extra electricity costs per year compared with compressor of same power. (Suppose the pressure difference of 2bar, the difference of energy consume is about 15 percent). In the longer time, it will be a great expense.
Loss of oil Every practical user knows that the gear box is first to be hurt at the state of losing oil. This problem does not exist in the Belt Driving System.
Efficiency Excellent gear transmission efficiency reaches 98-99% and excellent Belt Driving System efficiency reaches 99% at normal condition. The difference is not up to the choice of transmission but the design and the manufacture level of the manufacturer.
Structure noise For the gear transmission compressor, because of the rigid connection of the motor and the rotor, the vibration from the rotor of the compression room will be transmitted to the gear box and the motor bearing, which will not only increase wear of the motor bearing but also noise.
Design work pressure according to your requirement. Usually, the required pressure is not always the same with the standard type which provides by the manufacturer. For example, if the required pressure by the user is 10bar, the work pressure for the compressor may be 11 or 11.5bar according to the state of the equipment, the length of the piping and the degree of seal. Under this condition, a pressure rated 13bar compressor will be set and take the outlet pressure as the work pressure on the spot. The discharging capacity will keep the same, for the final work pressure decreased but the speed of the rotor does not increase. As the representative of modern technique, what the designer of the belt driving system need to do is to change the diameter of the pulley and make the work pressure completely the same with the requirement of the user. Thus, the user will get more air velocity with the same power motor. But for the gear transmission, it is not so easy.
11、Comparison Screw Compressor with Piston Compressor
Many people only pay attention to the price at time of purchase, but pay little attention to long use expenses involved in. Practice proves that piston compressor is the most expensive compressor.
1）、Saving electricity it saving money
Take a 20 cubic compressor as an example, the motor power of a screw compressor is 110 kw, but that of the piston compressor is 132 kw. It can save 22 kilowatt per hour. Suppose the work time is10 hours a day, it can save about: 22 times 10 times 365 equals to 80300 kilowatt per year. Ser vise three years, it will save more than 200 thousands yuan. Besides, double-screw compressor can save more than 60% electricity at no-loading, the piston compressor can only save about 10% electricity. If work time is 24 hours per day, 9 hours will be on no-loading, it can save 110kw×9hours×(60%-10%）=495 kilowatt/day, it will save 180000 kilowatt per year and 30000 kilowatt for three years.
2）、Save expense for Maintenance
Screw compressor is repair infrequent. If the routine maintenance has been done well, repair will be unnecessary. But the parts of the piston compressor need to be repaired frequently and it will greatly add the repair expense.
3）、Stable property
Maintenance done well, the screw compressor will not break down. But you don’t know when the piston will out of work. Think how much you lose when work stops for a day? For medium-large piston, man discharging is required to start again. Unsteady power will fire the motor; If it dries out, it may explode. The screw can work 24 hours continuously, but the piston cannot.
4）、Low noise
The screw is low in noise and can be placed in the workshop, which saves room. But the piston is high in noise, which will do harm to the workers.
5）、No Vibration
Reinforcement for a piston is a necessity, but not for a screw which only needs to be placed on the ground. Infinitesimal vibration which is negligible , may be caused by the electric machine.
6）、Not pollute the environment
The Piston is heavy on oil and need to be feed frequently. To a regular time, the bottom will be dark. But the Screw is always clean. The surrounding air of the Piston contains a large amount of oil. But it is only 1/80 of the Piston by the screw, which reaches the international standard of ISO8573.
So, most of medium/ large factory purchase the screw compressors.
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