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Fault analysis and solution of compressor frequently loading and unloading.

With the development of science and technology, air compressor, as an important power equipment widely used in machinery, metallurgy, building materials, electronic power, chemical, food, textile, and many other industrial fields.
However, in the long run, the compressor is bound to encounter a lot of fault problems, and the frequency of loading and unloading is one of them. Frequent actions not only shorten the life of the solenoid valve, compressor inlet door and unloading valve, but also threaten the safe operation of the whole unit.
The cause of the problem
What are the causes of frequent loading and unloading of compressors?
1) control reasons
It is well known that compressor's exhaust pressure is the main basis for compressor loading and unloading. If the difference between the two sets of values becomes smaller, it may result in frequent loading and unloading of the unit. When the load pressure value of the unit increases, the unloading pressure value decreases. Or simple loading pressure value increases, unloading pressure value will be reduced by unit and unloading cycle shorter, namely the unit under the condition of the gas constant, the closer the loading and unloading pressure value, and uninstall the more frequent, the greater the hidden trouble of safe operation of the equipment.
2) system reasons
If the pressure setting value of the unit is normal, there is no pipe blockage between the compressor outlet and the storage tank. If there are blocked but not completely when partition line, compressed air flow is obstructed, choke point between the compressor and gas pressure during the compressor load is very difficult to quickly discharge, result in a very short time to uninstall pressure value and unloading. And due to the choke point and the compressor export volume is limited, combined with the system loss (such as filter drainage with gas, person) and a small number of circulation to storage tanks, the pressure quickly to load pressure value, compressor and reload, and repeat.
Specifically, there are several factors:
(1) the pressure difference between the pressure controller and uninstall is too small, which may lead to the frequent loading and unloading of the unit.
(2) pressure sampling tube is blocked or leaked, and the pressure is attenuated too fast.
(3) the demand for compressed air during production is not stable, which is small or discontinuous when large.
(4) when the compressor unit is unloaded, the minimum pressure valve shall be closed less than or closed.
(5) load control solenoid valve fault. The solenoid valve should be inspected, which may be affected by the influence of the oil and water and the action is not sensitive or the coil is burnt out.
(6) failure or damage of the pressure sensor that controls the starting and stopping of the unit.
In case of the above problems, it should be solved in time, otherwise the equipment will be damaged and other faults will occur.
Treatment scheme
1. The control reason leads to frequent loading and unloading.
This reason can be displayed through unit and unloading pressure directly, if indeed change pressure sensor can be solved through online calibration or dismantled, detailed testing and back pack sensors can solve. Of course, it is also common for pressure sensors to measure the errors caused by the blockage of the pipes. The usual practice is to use compressed air to purge the sampling line.
2. The system causes frequent loading and unloading.
The processing of the system is complicated and can be judged by the difference between the outlet pressure of the compressor and the outlet pressure of the cooler. If the difference exists or the difference is too large (the general filter is less than 0.6bar, the cooler is greater than 0.2bar), then it can be judged that the pipe 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 easily blocked is:
1) except oil and water filter (after the dust filter is located in the cold dryer, the probability of general blocking is very small) : including filter core; Filter blowdown solenoid valve; Discharge solenoid valve front screen. It is the most likely to be blocked by the solenoid valve, which can be cleaned or replaced. And the discharge solenoid valve generally may appear valve body card, coil burn, timer bad phenomenon, general replacement can be solved. A plant ash compressor appeared because the water filter mesh jams before discharge solenoid valve, not timely drainage, make water filter in the compressor frequent unloading, maintenance personnel cleaning mesh after normal;
2) internal adsorption drying tower A and B inlet switch valve. Nowadays, many enterprises use adsorption desiccator after compressed air, and A and B tower are generally required to switch. If the switching valve is not in place, it can also cause the gas flow to be blocked. If the drying tower A and B inlet switch valve are pneumatic switch type, the pneumatic switch valve fault generally appears in the control air source and valve body two aspects. The maintenance personnel can determine whether the control air source is normal by checking whether there is water in the filter pressure relief valve or whether the gas source pipeline is off. The valve can also be manually operated to determine whether the valve body is flexible and the cylinder seals are good. If the control air source is clogged with the filter pressure reducing valve, the compressor will be frequently loaded and unloaded due to the uncontrollable switch valve. In view of this situation, the control air source sampling point can be changed to the outlet pipe of the cold dryer to solve the problem of controlling the air supply.
3) if the temperature adjustment of the precooler and evaporator is not good, it is also easy to cause the evaporator to enter and exit most of the ice blockage, thereby impeding the flow of gas. It can be judged by the observation method that the temperature adjustment of ice blocking or evaporator can be observed, if the compressed air pipeline in the cooler is "sweating"; The parameter setting of the cold dryer does not meet the requirements of the equipment design, and should be adjusted in time to avoid unnecessary losses caused by the freezing equipment. In this case, the temperature of evaporator can be solved by adjusting the temperature of the evaporator.
4) the installation error of the outlet valve of the dust filter or the valve rod and valve body will also cause the compressor to be loaded frequently. Had happened once because the factory repair dust removal filter outlet check valve leakage defects due to negligence, the way the valve after lead to compressed air can not flow into the air tank, the gas can go back in the store jar back to the person who caused by frequent and unloading unit.
3. Unstable air volume leads to frequent loading and unloading.
In this case, the method of adding storage tanks is generally adopted, or the volume of the original storage tank can be increased. If the filling tank can not meet the production needs, it is recommended to replace the original working frequency unit with the converter compressor. In addition to the damage caused by frequent loading and unloading, the frequency conversion compressor has other advantages:
(1) pressure stabilization
Because of the frequency conversion of the screw compressor, the inverter can be easily started by the PID regulator inside the controller or inverter. The response can be adjusted quickly in the case of large fluctuation of gas volume.
Compared with the upper and lower limit switch control, the pressure stability is improved exponentially.
(2) start no impact.
Because the inverter itself containing the function of soft starter and starting current biggest within 1.2 times the rated current, and power frequency start generally in more than 6 times of the rated current, compared to start the impact is very small. The impact is not only on the grid, but also on the entire mechanical system.
(3) variable flow control.
The frequency - driven compressors can only work in one discharge volume, and the frequency conversion compressor can work in a wide range of displacement. The frequency converter is to adjust the motor speed in real time to control the discharge volume. When the gas is low, the compressor can automatically sleep, which greatly reduces the loss of energy.
(4) the voltage adaptability of ac power supply is better.
The frequency converter with the modulation technology can 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 result in the high voltage output to the motor. In the case of spontaneous electricity, frequency conversion drive can show its advantages.
(5) low noise
Most of the operating conditions of the frequency conversion system are below the rated speed. The mechanical noise and wear of the main engine are reduced, and the maintenance and service life are extended. If the fan also adopts variable frequency drive, it can significantly reduce the noise of the compressor.
The maintenance and maintenance of the compressor is the objective requirement of the compressor's own movement, especially for the compressor. Only by insisting on regular inspection and timely replacement of relevant parts, can the normal nature of mechanical work be guaranteed, so as to ensure the continuity and stability of the production and bring higher benefits to the enterprise.

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