With the development of science and technology, air compressors, as an important power equipment, are widely used in many industrial fields such as machinery, metallurgy, building materials, electronic power, chemical industry, food, textile and so on.

However, in the long-term operation of the compressor, there will inevitably be many failure problems, and frequent loading and unloading is one of them. Frequent actions not only shorten the life of the unit's solenoid valve, compressor inlet door and unloading valve, but also seriously threaten the safe operation of the entire unit.
  cause of issue
What are the reasons for the frequent loading and unloading of the compressor?
1) Control reasons
As we all know, the discharge pressure of the compressor is the main basis for controlling the loading and unloading of the compressor. If the difference between the two set values ​​becomes smaller, it may lead to frequent loading and unloading of the unit. When the loading pressure value of the unit increases, the unloading pressure value decreases at the same time; or simply the loading pressure value increases and the unloading pressure value decreases, which will shorten the loading and unloading cycle of the unit. The closer the value is, the more frequent the loading and unloading, and the greater the hidden danger of the safe operation of the equipment.
2) System reasons
If the set value of the unit loading and unloading pressure is normal, it can be considered whether there is pipeline blockage between the compressor outlet and the gas storage tank. If the pipeline is blocked but not completely blocked, the flow of compressed air will be severely blocked, and the gas pressure between the blockage point and the compressor is difficult to be quickly relieved during the loading of the compressor, resulting in the unloading pressure value reaching the unloading pressure value in a very short time. . However, due to the limited air volume between the blockage point and the compressor outlet, coupled with system losses (such as filter drainage with air, air dryer regeneration) and a small amount of circulation to the air storage tank, the pressure quickly drops to the loading pressure value, the compressor Reloaded again, and so on.
Specifically, there are the following factors:
(1) The set value of the pressure difference between the loading and unloading of the pressure controller is too small, which may lead to frequent loading and unloading of the unit.
(2) The pressure sampling tube is blocked or leaked, and the pressure decays too quickly.
(3) The demand for compressed air during production is unstable, ranging from large to small or discontinuous.
(4) When the compressor unit is unloaded, the minimum pressure valve is not closed in time or not strictly.
(5) The loading control solenoid valve is faulty. The solenoid valve should be checked, it may be affected by oil, water and gas, which may cause the action to be insensitive or the coil is burned out.
(6) The pressure sensor that controls the start and stop of the unit is faulty or damaged.
When encountering the above problems, it should be solved in time, otherwise it will cause damage to related equipment and other failures.
Solution
1. The treatment method for frequent loading and unloading caused by control reasons
This kind of reason can be directly seen through the pressure display when the unit is loaded and unloaded. If there is any change, it can be solved by online calibration or by removing the pressure sensor, checking in detail and reinstalling the sensor. Of course, it is also common for the pressure sensor measurement pipeline to be blocked and cause measurement errors. The usual practice is to use compressed air to purge the sampling pipeline.
2. Handling methods for frequent loading and unloading caused by system reasons
The treatment of the system reason is more complicated, which can be judged by the difference between the compressor outlet pressure and the refrigerating machine outlet pressure. If there is a difference or the difference is too large (generally the filter is less than or equal to 0.6bar, and the dryer is more than or equal to 0.2bar), it can be judged that the pipeline or equipment is blocked. Since there are many equipments in this pipeline, after long-term maintenance and observation, it is found that the equipments that are often blocked are:
1) Oil removal and water removal filter (the dust removal filter is located behind the refrigerating machine, and the probability of blockage is generally small): including the filter core; the filter drain solenoid valve; the filter screen in front of the drain solenoid valve. Among them, the filter screen in front of the sewage solenoid valve is most likely to be blocked, which can be solved by cleaning or replacement. The blowdown solenoid valve generally has the phenomenon of valve body jamming, coil burning, timer failure, etc., which can be solved by replacing it. In a factory, the ash removal compressor once occurred because the filter screen in front of the drainage solenoid valve of the water removal filter was blocked, and the sewage could not be discharged in time. The sewage filled the filter and caused the compressor to be frequently loaded and unloaded. After the maintenance personnel cleaned the filter screen, it was normal;
2) The inlet switching valve of adsorption drying tower A and B inside the refrigeration dryer. At present, many companies use adsorption dryers for post-processing of compressed air, and generally need to switch between A and B towers. If the switching valve is not switched in place, it can also cause the gas flow to be blocked. Some of the inlet switching valves of the drying towers A and B of the refrigeration dryer are pneumatic switch type, and the fault of the pneumatic switch type valve generally occurs in the control air source and the valve body. Maintenance personnel can judge whether the control air source is normal by checking whether there is water in the filter pressure reducing valve or whether the air source pipeline is falling off; they can also manually operate the pneumatic valve to judge whether the valve body is flexible and the cylinder is tight. good. If the control air source with water blocks the filter pressure reducing valve, the compressor will be frequently loaded and unloaded due to the inability to control the switching valve. In view of this situation, the sampling point of the control air source can be changed to the outlet pipe of the refrigeration dryer to solve the problem of water in the control air source;
3) If the temperature of the precooler and the evaporator in the refrigerating machine is not well adjusted, it is easy to cause ice blockage in most of the inlet and outlet of the evaporator, thus hindering the flow of gas. The occurrence of ice blockage or improper adjustment of the evaporator temperature can be judged by observation. If there is a phenomenon of "sweat" in the compressed air pipeline in the freezer; or the parameter settings of the freezer do not meet the equipment design requirements, adjustments should be made in time to avoid Frozen equipment causes unnecessary losses. This situation occurs more frequently during seasonal changes, and is generally solved by properly adjusting the temperature of the evaporator;
4) The wrong installation of the check valve at the outlet of the dust filter or the falling off of the valve stem and the valve body will also cause the compressor to be frequently loaded and unloaded. The above-mentioned factory once happened because after overhauling the leakage defect of the check valve at the outlet of the dust filter, the direction of the valve was negligently installed, so that the compressed air could not flow into the gas storage tank, and the gas in the gas storage tank could flow back to the cold dryer. Cause frequent loading and unloading of the unit.
3. Unstable gas consumption leads to frequent loading and unloading processing
In this case, the method of adding a gas storage tank is generally adopted, or the volume of the original gas storage tank is increased. If the installation of the air storage tank cannot meet the production needs, it is recommended to use the inverter compressor to replace the original power frequency unit. In addition to solving the harm caused by frequent loading and unloading, the inverter compressor has other advantages:
(1) The air pressure is stable
Since the variable frequency screw compressor generally utilizes the stepless speed regulation feature of the frequency converter, it can start smoothly through the controller or the PID regulator inside the frequency converter; it can quickly adjust the response when the gas consumption fluctuates greatly.
Compared with the upper and lower limit switch control of power frequency operation, the air pressure stability is exponentially improved.
(2) Start without impact
Since the inverter itself contains the function of a soft starter, the maximum starting current is within 1.2 times of the rated current. Compared with the power frequency starting that is generally more than 6 times the rated current, the starting impact is very small. This kind of impact is not only on the power grid, but also on the entire mechanical system, which is also greatly reduced.
(3) Variable flow control
The compressor driven by power frequency can only work in one displacement, and the inverter compressor can work in a wide range of displacement. The frequency converter adjusts the motor speed in real time according to the actual gas consumption to control the exhaust gas volume. When the gas consumption is low, the compressor can be automatically put to sleep, which greatly reduces the loss of energy.
(4) The voltage adaptability of the AC power supply is better
The inverter using overmodulation technology can still output enough torque to drive the motor when the AC power supply voltage is slightly lower; when the voltage is slightly higher, it will not cause the output voltage to the motor to be too high. For the occasion of self-generating, the variable frequency drive can better show its advantages.
(5) Low noise
Most of the working conditions of the frequency conversion system work below the rated speed, the mechanical noise and wear of the host machine are reduced, and the maintenance and service life are prolonged. If the fan is also driven by variable frequency, the noise of the compressor can be significantly reduced.
Conclusion
The maintenance of the compressor is an objective requirement for the movement of the compressor itself, and it is especially important for the compressor (device). Only by insisting on regular inspection and timely replacement of relevant parts, can the normality of mechanical work be ensured, thereby ensuring the continuity and stability of enterprise production, and bringing higher benefits to the enterprise.