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Fault Analysis and Solution of Frequent Load and Unload of Compressor
Classification: News dynamics
Classification: Company News
Time：2017-10-13 12:01
With the development of science and technology, air compressor as an important power equipment, is widely used in machinery, metallurgy, building materials, electronic power, chemical industry, food, textile and many other industrial fields. However, in the long-term operation of the compressor, it is bound to encounter many failures, and frequent loading and unloading is one of them. Frequent actions not only shorten the life of the unit solenoid valve, compressor inlet valve and unloading valve, but also seriously threaten the safe operation of the whole unit. What are the reasons for the frequent loading and unloading of the compressor caused by the failure? 1) The control reasons are well known, and the pressure
With the development of science and technology, air compressor as an important power equipment, is widely used in machinery, metallurgy, building materials, electronic power, chemical industry, food, textile and many other industrial fields.
However, in the long-term operation of the compressor, it is bound to encounter many failures, and frequent loading and unloading is one of them. Frequent actions not only shorten the life of the unit solenoid valve, compressor inlet valve and unloading valve, but also seriously threaten the safe operation of the whole unit.
Cause of failure
What are the reasons for the frequent loading and unloading of the compressor?
1) Reasons for control
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 cause 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 increase of the loading pressure value and the decrease of the unloading pressure value will shorten the loading and unloading cycle of the unit, that is, under the condition of constant gas consumption, the closer the loading and unloading pressure values are, the more frequent the loading and unloading are, and the greater the hidden danger of safe operation of the equipment.
2) System reasons
If the set value of the loading and unloading pressure of the unit is normal, it can be considered whether there is pipeline blockage between the compressor outlet and the air storage tank. If the pipeline is blocked but not completely cut off, the compressed air circulation will be seriously blocked, and the gas pressure between the blockage point and the compressor is difficult to quickly unload during the loading of the compressor, resulting in a very short time to reach the unloading pressure value and unloading. 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, regeneration of cold dryer) and a small part of circulation to the air storage tank, the pressure quickly drops to the loading pressure value, and the compressor is reloaded again, so repeatedly.
Specifically, there will be the following factors:
(1) The pressure difference between the pressure controller and the unloading is too small, which may lead to frequent loading and unloading of the unit.
(2) The pressure sampling pipe is blocked or leaked, and the pressure decays too fast.
(3) The demand for compressed air required for production is unstable, sometimes large and sometimes small or discontinuous.
(4) When the compressor unit is unloaded, the minimum pressure valve is not closed in time or is not closed tightly.
(5) loading control solenoid valve failure. Should check the solenoid valve, may be affected by the oil and water gas caused by the action is not sensitive or the coil burned out.
(6) The pressure sensor that controls the start and stop of the unit is faulty or damaged.
When encountering the above problems, they should be solved in time, otherwise it will cause damage to related equipment and other failures.
Treatment Scheme
1. Handling methods for frequent loading and unloading due to control reasons
This reason can be directly seen from the pressure display when the unit is loaded and unloaded. If there is any change, it can be solved by online calibration or removal of the pressure sensor, detailed detection and re-installation of the sensor. Of course, the pressure sensor measurement pipeline due to blockage caused by measurement error phenomenon is also relatively common, the usual practice is to use compressed air purging sampling pipeline can be.
2. Handling methods for frequent loading and unloading caused by system reasons
The system reason processing is more complicated, which can be judged by the difference between the outlet pressure of the compressor and the outlet pressure of the cold dryer. If there is a difference or the difference is too large (general filter ≤ 0.6bar, cold dryer ≥ 0.2bar), it can be judged that the pipeline or equipment is blocked. Due to the large number of pipeline equipment, after long-term maintenance and observation, it is found that the equipment that is often easily blocked are:
1) Oil removal and water removal filters (dust removal filters are located after the cold dryer, and the probability of general blockage is very small): including filter core; Filter blowdown solenoid valve; Filter screen before blowdown solenoid valve. Among them, the probability of plugging the filter screen before the sewage solenoid valve is the largest, which can be solved by cleaning or replacement. The blowdown solenoid valve may generally appear valve jam, coil burn, timer is bad and other phenomena, the general replacement can be solved. The ash removal compressor in a factory was once blocked by the filter screen in front of the sewage discharge solenoid valve of the water removal filter, which could not discharge sewage in time. As a result, the sewage filled with the filter led to frequent loading and unloading of the compressor, and the maintenance personnel cleaned the filter screen normally;
2) The inlet switching valve of adsorption drying tower A and B inside the cold dryer. At present, many enterprises adopt adsorption dryer for compressed air post-treatment, which generally needs to switch between A and B towers. If the switching valve is not switched in place, the gas flow can also be blocked. If the inlet switching valve of drying tower A and B of the air dryer is of pneumatic switch type, the failure of pneumatic switch type valve generally occurs in both the control air source and the valve body. The maintenance personnel can judge whether the control gas source is normal by checking whether there is water in the filter pressure reducing valve or whether the gas source pipeline falls off. You can also manually operate the pneumatic valve to judge whether the valve body is flexible and whether the cylinder seal is good. If the control air source with water to block the filter pressure relief 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 cold dryer to solve the problem of water in the control air source;
3) If the temperature adjustment of the pre-cooler and evaporator in the cold dryer is not good, it is also easy to cause most of the ice blockage at the inlet and outlet of the evaporator, thus hindering the gas circulation. Ice blockage or improper temperature adjustment of the evaporator can be judged by observation. If the compressed air pipe in the cold dryer has "sweating" phenomenon; Or the parameter setting of the cold dryer does not meet the equipment design requirements, it should be adjusted in time to avoid unnecessary losses caused by freezing the equipment. This situation occurs more often during seasonal changes and is generally resolved by appropriate adjustment of the evaporator temperature;
4) The wrong installation of the check valve at the outlet of the dust removal filter or the fall of the valve stem and the valve body will also cause frequent loading and unloading of the compressor. The above-mentioned factory once happened that the compressed air could not flow into the air storage tank due to the negligence of installing the valve in the reverse direction after repairing the internal leakage defect of the check valve at the outlet of the dust removal filter, and the gas in the air storage tank could flow back to the cold dryer, resulting in frequent loading and unloading of the unit.
3. Frequent loading and unloading due to unstable gas consumption
In this case, the method of installing a gas tank is generally adopted, or the volume of the original gas tank is increased. If the installation of air storage tank can not meet the production needs, it is recommended to use the frequency conversion compressor to replace the original power frequency unit. In addition to solving the hazards caused by frequent loading and unloading, inverter compressors have other advantages:
(1) Stable air pressure
Because the variable frequency screw compressor generally uses the stepless speed regulation characteristics of the frequency converter, through the controller or the PID regulator inside the frequency converter, it can start smoothly; 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 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, which is generally more than 6 times of the rated current, the starting impact is very small. This impact is not only on the power grid, but also on the entire mechanical system.
(3) Variable flow control
The compressor driven by power frequency can only work in one displacement, and the variable frequency compressor can work in a relatively wide range of displacement. The frequency converter is based on the actual gas consumption to adjust the motor speed in real time to control the displacement. When the gas consumption is low, the compressor can also be automatically dormant, which greatly reduces the loss of energy.
(4) The voltage adaptability of AC power supply is better
The frequency converter using over-modulation technology can still output sufficient 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 voltage output to the motor to be on the high side. For self-generating occasions, variable frequency drive can show its advantages.
(5) Low noise
Most of the working conditions of the frequency conversion system are lower than the rated speed, and the mechanical noise and wear of the main engine are reduced, which prolongs the maintenance and service life. If the fan is also driven by frequency conversion, the noise of the compressor can be significantly reduced.
The maintenance of the compressor is the objective requirement of the compressor's own movement, and it is particularly important for the compressor (device). Only by adhering to regular inspection and timely replacement of relevant parts, can we ensure the normality of mechanical work, so as to ensure the continuity and stability of enterprise production, and bring higher benefits to enterprises.