Understand the principle and structure of air compressor, this article must be read!

1、 Understand the principle and structure of air compressor

1. Motor

*Generally, 380V motors are used for motors below 250KW, and 6kV and 10kV motors are generally used for motors above 250KW.

*The explosion-proof air compressor is 380V / 660V. The wiring mode of the same motor is different, and the two voltages of 380V and 660V can be selected. The high pressure marked on the nameplate of the explosion-proof machine is 0.7MPa, and the national standard of 0.8MPa is not available. The production license issued by the state indicates 0.7MPa, which can reach 0.8MPa in actual use.

*The air compressor is equipped with 2-pole and 4-pole asynchronous motors.

*The speed of 2-pole synchronous motor is 3000r / min, and the speed of 2-pole asynchronous motor of air compressor is ≥ 3000 × 97% = 2910 R / min, generally 2960 R / min for users, and 3% is the speed difference.

*The speed of 4-pole synchronous motor is 1500r / min, and the speed of 4-pole asynchronous motor of air compressor is ≥ 1500 × 97% = 1455 R / min, generally 1480 R / min for users, and 3% is speed difference.

*There are only 2-pole and 4-pole motors matched with the air compressor, and the rotation speed can be regarded as a constant (1480 R / min and 2960 R / min) according to the national standard.

*Service coefficient: all motors in the air compressor industry are non-standard motors, which is a status quo of large machines and small standards. The service coefficient is generally 1.1-1.2. For example, the service factor of the motor of the 200kW air compressor is 1.15, so the high power of the motor of the air compressor can actually reach 200 × 1.15 = 230kw, 15% of the power is reserved when telling the user, which belongs to additive feeding.

*Ordinary motor is a status quo of small machine and large standard. For example, it is good that a 100kW motor can output 80% of the power. The common saying is that the power factor cos ∮ = 0.8, which is cheating.

*Protection grade: refers to the waterproof and dust-proof grade of the motor. Generally, IP23 is enough. However, in the air compressor industry, 380V motors are basically IP55 and IP54, 6kV and 10kV motors are basically IP23, and some customers require IP55 or IP54.

*Insulation level: refers to the ability level of the motor to resist high temperature and burn. Generally, level F is used, and level B temperature rise assessment refers to the standard assessment one level higher than level F.

*Startup mode: startup mode of star triangle conversion.

2. Screw compressor host

*Compressor: it is a kind of machinery for raising gas pressure; The core component of the screw compressor is the main engine, commonly known as the head; The technical core of the main engine is the screw pair, that is, the male and female rotors. The thick is the male rotor and the thin is the female rotor.

*Main engine: the main structure is composed of rotor, casing (cylinder), bearing and shaft seal. To be exact, two rotors (a pair of female and male rotors) are installed in the casing with bearings at both ends to suck the air from one end. By the relative rotation of the male and female rotors, the tooth top engages with the tooth groove to compress the air, increase the pressure of the gas, and then discharge it from the other end.

*The main engine needs power input, cooling, sealing and lubrication during gas compression. Therefore, the main engine must be installed in the air compressor system before it can work.

*Why is the screw machine a high-tech product?, This is because the mainframe is a high-tech product.

*There are two main reasons why the host machine is called a high-tech product: ① the processing accuracy is very high, and it can be processed by non ordinary equipment; ② The rotor is a three-dimensional space surface, and its profile is only in the hands of a few foreign companies.

*From the structure of the main engine, there is no contact between the male and female rotors, with a gap of 2-3 wires. There is also a gap of 2-3 wires between the rotor and the casing, which is also non-contact and non friction. The clearance between the rotor end face and the casing is 2-3 wires, which is also non-contact and non friction. Therefore, the service life of the main engine mainly depends on the service life of the bearing and shaft seal.

*The service life of bearing and shaft seal, i.e. the replacement period, is related to its stress condition and speed. Therefore, the service life of the direct connected main engine with low rotation speed and no additional force on the bearing is long. On the contrary, the main engine speed of the belt conveyor is high, and the bearing is stressed, so its service life is short.

*The main engine bearing is installed by special installation tools in the constant temperature and humidity workshop, which is a highly technical work. Once the bearing is damaged, especially the main engine, it must be returned to the professional maintenance factory for replacement. In addition, the time for round-trip transportation and maintenance will cause great trouble to the user. In terms of time, the user can not afford to delay. Once the air compressor is stopped, the entire production line will have to be stopped, and the workers will have to take a holiday. The industrial output value affected every day is tens of thousands. Therefore, in the spirit of being responsible to the user, we recommend low-speed direct connection without speed increasing gear as much as possible.

3. Structure and separation principle of oil separator

*The oil separation tank is a tank that can separate the mixture of oil and gas. The oil drum is generally a cylindrical carbon steel skin tank made of 45 # steel welded. The oil drum made of stainless steel is very rare and generally not used. Another function is to store lubricating oil. There is an oil-gas separation filter element in the oil separator tank, which is referred to as the oil separator core. The oil separator core is generally made of about 23 layers of imported glass fiber layers, and a few of them may only have about 18 layers.

*Its working principle is that when the mixture of oil and gas passes through the glass fiber layer at a certain flow rate, the oil droplets are blocked by the physical machinery and slowly condensed into large oil droplets. Then, under the action of gravity, they fall to the bottom of the oil core. Then, there is a return pipe to introduce the oil filtered into the bottom of the oil core into the machine head and participate in the next cycle. There is a one-way valve on the oil return pipe, so that the oil can only flow into the compression chamber of the main engine from the bottom of the oil core.

*In fact, before the oil-gas mixture penetrates the oil separator core, 99% of the oil in the oil-gas mixture has been separated to the bottom of the oil separator tank.?

*The high-pressure and high-temperature (about 80 ℃) oil-gas mixture from the main engine enters the oil drum along the tangential direction inside the oil drum. Under the action of centrifugal force, most of the oil in the oil-gas mixture is thrown onto the inner wall of the oil drum and flows along the inner wall to the bottom of the oil drum under the action of gravity. Another part of the oil droplets condense into large oil droplets in the process of collision with each other, and also sink to the bottom of the oil separator tank under the action of gravity to participate in the next cycle.

*The air filtered by the oil core will flow to the rear cooler through the small pressure maintenance valve (small pressure valve) for cooling and then be discharged from the air compressor.

*The small pressure maintenance valve is also a one-way valve, which can be called the exhaust valve on the oil drum. Located at the outlet of the oil-gas separator above the oil-gas drum, the opening pressure is set to about 0.45MPa. The small pressure valve mainly has the following functions:

(1) When starting, the circulating pressure required by lubricating oil shall be established first to ensure the lubrication of the machine

(2) The oil-gas drum can be opened only after the gas pressure exceeds 0.45MPa, which can reduce the air flow rate through the oil-gas separator, not only ensure the effect of the oil-gas separator, but also protect the oil-gas separator from damage due to too large pressure difference.

(3) Check function: when the pressure in the oil and gas barrel drops after shutdown, the compressed air in the pipeline is prevented from flowing back.

*There is a safety valve on the end cover of the oil drum. When the air pressure in the oil drum reaches 1.1 times of the set value, the safety valve will automatically open to release some air and reduce the air pressure in the oil drum. The way to check the safety valve is to gently pull the air release lever on the safety valve when the compressor is fully loaded. If the safety valve can discharge air, it is considered normal.

*A pressure gauge is installed on the oil drum to detect the pressure before filtration. A blowdown valve is installed at the bottom of the oil drum. The blowdown valve shall be opened regularly to drain the water and dirt deposited at the bottom of the oil drum.

*There is a transparent oil level mirror beside the oil drum to display the oil level in the oil drum. The correct oil level is that when the air compressor works normally, the oil level is in the middle of the upper and lower degrees. If the oil level is too high, it will run away. If the oil level is too low, it will affect the safety of the whole machine.

*The oil drum is produced by a professional manufacturer with manufacturing qualification for pressure vessels. Each oil drum has a number and certificate of conformity.

4. Cooler

*The oil cooler and the compressed air aftercooler of the air-cooled screw machine are integrated into an aluminum plate fin structure, which is brazed and formed in the vacuum furnace. Once the oil leaks, it is almost impossible to repair and only can be replaced. Its working principle is that hot oil and high-temperature (about 80 ℃) gas flow in their respective pipes, the motor drives the fan to rotate, and the cold air vertically blows the pipes with hot oil and high-temperature gas to realize heat exchange. The air after heat exchange through the radiator will feel very hot.

*The water-cooled screw machine generally uses a tube radiator. The water flows in the tube and the hot oil flows outside the tube. After heat exchange, the cold water becomes hot water. Many manufacturers often use steel pipes instead of copper pipes to reduce costs. Another cooling tower must be built for the water cooler to cool the hot water after heat exchange so as to participate in the next cycle. The water quality has a great impact on the radiator, and the cooling tower adds a lot of costs. Therefore, the amount of water cooler is far less than that of the air cooler. However, in places with large dust, such as cement plants, workshops with fusible dust, such as spraying workshops, the water cooler should be used as much as possible. Once the water-cooled radiator is scaling, it is difficult to clean it. Generally, it must be soaked with chemical water for several days, and then blown with high-pressure water or high-pressure air. The amount of cooling water for the water cooler is specified in JB / t6430-2002. About 4 liters of water is required for each 1m3 of compressed air.

*In principle, the hot air from the air-cooled radiator must be led out by the air guide cover or the hot air must be discharged from the air compressor room as effectively as possible in a very effective way, such as adding an industrial fan to extract the hot air.

*The hot air flowing out of the radiator cannot be effectively discharged, and if it participates in the air circulation of the air compressor, the result will be catastrophic high-temperature shutdown.

*The compressed air cooled by the aftercooler contains a large amount of moisture, most of which can be separated from the air tank.

*Compressed air temperature after cooling: the water cooler is about 10 ℃ higher than the ambient temperature, and the air-cooled type is about 15 ℃ higher than the ambient temperature.

5. Temperature control valve

*The exhaust temperature of the exhaust end of the main engine is controlled mainly by controlling the temperature of the lubricating oil injected into the main engine. If the exhaust temperature of the machine head is too low, moisture will be separated out in the oil drum, resulting in emulsification of the lubricating oil. When the oil temperature is ≤ 70 ℃, the temperature control valve controls the lubricating oil from entering the cooler. When the oil temperature is > 70 ℃, the temperature control valve only allows part of the hot oil to be cooled through the oil cooler, and the cooled oil is mixed with another part of the uncooled hot oil to enter the main engine. When the oil temperature is ≥ 76 ℃, the temperature control valve opens all the channels to the oil cooler. At this time, all the hot lubricating oil is cooled by the oil cooler and then enters the main engine for compression.

*The temperature control valve can be understood as the temperature control valve of the oil entering the machine head

6. PLC and display

*PLC can be understood as the host of a computer, and the LCD screen of the air compressor can be understood as the display screen of a computer. PLC has the functions of input, output (to display screen), calculation and storage.

*The screw machine is turned into a highly intelligent fool machine by PLC. Any fault of any component of the air compressor will be reflected on the display screen by PLC for maintenance.

*When it is time to replace the air filter, machine filter, oil core and lubricating oil of the air compressor, the PLC will automatically give an alarm for replacement.

2、 Other components of screw air compressor

1. Air filter

*The air filter element is a paper dry filter, which is the core of air filtration. The folded shape is made to increase the air penetration area.

*The ventilation fine hole of the air filter element is about 3 μ M U.M. the main function is to filter the air with a concentration of more than 3 μ M U.M dust and solid particles to avoid premature wear of screw rotor and premature blockage of oil filter and oil core. In general, take down and blow air ≤ 0.3MPa from the inside to the outside every 500 hours or less (depending on the specific environment) to clean and dredge the blocked ventilation pores. If the pressure is too high, the pores will be blown out and blown large, and on the contrary, the filtering accuracy requirements will not be met. Therefore, when blowing the filter element with the remaining air in the air tank, it is necessary to see clearly the pressure indicated by the pressure gauge on the air tank. Be careful that the air of > 0.3MPa will blow the air filter element out of service, which will cause the air filter element to fail and cause the head to lock.

2. Intake valve

*It is also called the intake control valve, through which the air flow into the main engine is controlled, so as to control the exhaust volume of the air compressor.

*The adjustable intake valve controls the servo cylinder by the anti proportional valve, and the ejector rod of the servo cylinder pushes the valve piece in the intake valve to control the intake air quantity, which can realize stepless intake control and adjustment from 0% to 100%.

3. Inverse example valve and servo cylinder:

*The proportion refers to the air distribution ratio between the two air paths a and B, which means the opposite. That is, the smaller the air volume entering the servo cylinder through the anti proportional valve, the larger the opening of the valve plate of the intake valve, and vice versa.

4. Vent solenoid valve

Next to the air inlet valve, when the air compressor is stopped, the air in the oil separator tank and the main engine is vented to the upper part of the air inlet valve plate and discharged through the air filter to avoid the heavy start of the air compressor due to the oil in the main engine when the air compressor is restarted, and then increase the starting current and burn the electric machine

5. Temperature sensor

It is located at the exhaust end of the main engine. It measures the temperature of the oil-gas mixture discharged from the main engine. The other end is connected to the PLC and displays the temperature on the LCD?

6. Pressure sensor

It is located at the exhaust end of the air compressor, i.e. the air outlet. Measure the air pressure after the oil separator is discharged. The air pressure before the oil separator is filtered is called the pre filter pressure. When the difference between the pre filter pressure and the post filter pressure is ≥ 0.1MPa, the oil separator should be replaced. The other end is connected to PLC and the pressure is displayed on the display screen. A pressure gauge is installed outside the oil drum to detect the pressure before filtration and the pressure after filtration is displayed on the electronic screen

7. Machine filter

The machine filter is the abbreviation of the oil filter. The oil filter is a paper filter with a filtering accuracy of 10-15 microns. Its function is to remove metal particles, dust, oxide and gum in the oil to protect the bearing and rotor from normal lubrication. Clogging of the oil filter will lead to poor oil supply of the machine head, affect the bearing life, cause high exhaust temperature, and cause local carbon deposition

8. Oil return check valve: the residual oil filtered by the oil-gas separator is concentrated in the small circular groove at the bottom of the oil separator and led to the main engine through the oil return pipe to prevent the separated lubricating oil from being discharged with the air. To prevent oil backflow in the compression chamber of the main engine, a one-way valve is set behind the oil return pipe. If the oil consumption suddenly increases during the operation of the machine, check whether the throttle hole of the one-way valve is blocked

9. Various oil pipes in the air compressor

It is the oil circulation pipe. The oil pipe through which the high-temperature and high-pressure oil-gas mixture discharged from the main engine passes must be covered with bellows to prevent high-pressure explosion. The oil return pipe connecting the oil drum to the machine head is generally iron.

10. Fan for cooling radiator

Generally, the axial flow fan is used, which is driven by a small motor to make the cold air blow vertically through the radiator. Some models do not have temperature control valves, but control the oil temperature by controlling the fan motor to stop. When the exhaust temperature rises to 85 ℃, the fan starts to operate; When the exhaust temperature is lower than 75 ℃, the fan will automatically stop to keep the temperature within a certain range. For the model with temperature control valve, the start and stop of fan are the same as above

The above contents are sorted and shared by the compressed air pipeline manufacturer Dalian paipulu Technology Co., Ltd.