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Analysis and solution of compressor frequent loading and unloading fault



Analysis and solution of compressor frequent loading and unloading fault

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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 other industrial fields.However, in the long run of......

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 other industrial fields.


However, in the long run of the compressor, it is inevitable to encounter a lot of fault problems, loading and unloading frequently is one of them.Frequent action not only shortens the service life of the solenoid valve, compressor inlet door and unloading valve, but also poses a serious threat to the safe operation of the whole unit.

The cause of the problem

What are the reasons for frequent loading and unloading of compressor?

1) control the causes

As is known to all, the exhaust pressure of the compressor is the main basis to control 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 of the unit increases, the unloading pressure decreases.Or simply increasing the loading pressure value and decreasing the unloading pressure value will shorten the loading and unloading cycle of the unit, that is, the closer the loading and unloading pressure value is to the unit under the condition of constant gas consumption, the more frequent the loading and unloading will be, and the greater the hidden danger of the safe operation of the equipment will be.

2) system reasons

If the set value of the unit's loading and unloading pressure is normal, it is possible to consider whether there is pipeline blockage between the compressor outlet and the gas 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 plugging point and the compressor is difficult to be removed quickly during the loading of the compressor, resulting in the unloading pressure will be reached in a very short time.Due to the limited air volume between the plugging point and the compressor outlet, coupled with the system loss (such as filter drainage zone gas, regeneration of the cold dryer) and a small part of the circulation to the gas storage tank, the pressure soon fell to the loading pressure value, the compressor reload, so repeated.

Specific points, there will be the following factors:

(1) if the pressure difference between the loading and unloading of the pressure controller is too small, it may lead to frequent loading and unloading of the unit.

(2) the pressure sample tube is blocked or leaked, and the pressure attenuation is too fast.

(3) the demand for compressed air during production is unstable, sometimes large, sometimes small or discontinuous.

(4) when unloading the compressor unit, the minimum pressure valve is not closed or closed properly.

(5) failure of load control solenoid valve.Solenoid valve should be checked, may be affected by oil, water and gas caused by insensitive action or coil burn.

(6) failure or damage of the pressure sensor that controls the start and stop of the unit.

In the event of the above problems, should be timely solved, or it will cause the related equipment damage and other failures.

Treatment scheme

1. Control the causes of frequent loading and unloading

This reason can be directly seen from the pressure display of unit loading and unloading. If there is any change, the pressure sensor can be solved through online calibration or removed, and the sensor can be tested in detail and replaced.Of course, the pressure sensor measurement pipeline due to the blockage of the measurement error phenomenon is also more common, the usual practice is to use compressed air purge sampling pipeline.

2. Handling methods of frequent loading and unloading caused by system reasons

The reason of the system is complicated, which can be judged by the difference between the outlet pressure of the compressor and the outlet pressure of the cold dryer.If the difference exists or is too large (the general filter ≤0.6bar, the cold dryer ≥0.2bar), it can be judged that the pipeline or equipment is blocked.As there are many equipment in this section of pipeline, it is found after long-term maintenance and observation that the equipment that is often blocked is:

1) oil and water removal filter (dust removal filter is located after the cold dryer, the probability of blocking is very small) : including the filter core;Filter blowdown solenoid valve;Drain solenoid valve front screen.Among them to discharge solenoid valve before the probability of blockage of the filter is the largest, can be cleaned or replaced by the solution.And blowdown solenoid valve may appear in general valve body block acrid, coil burnt out, timer bad phenomenon, general replacement can be solved.The ash removal compressor in a factory was once blocked by the filter screen in front of the discharge solenoid valve of the water removal filter, so that the sewage could not be discharged in time, which led to the frequent loading and unloading of the compressor.

2) switch valve for A and B inlet of adsorption drying tower inside the cold dryer.Now, many enterprises use adsorptive dryer for compressed air post-treatment, which generally requires tower A and tower B switching.If the switching valve is not in place, the gas flow may be blocked.If the inlet switch valve of tower A and B of the dryer is pneumatic switch valve, the fault of pneumatic switch valve generally appears in the control of air source and valve body.The maintenance personnel can judge whether the control air source is normal by checking whether there is water accumulation in the filter pressure reducing valve or whether the air source pipeline falls off.It is also possible to determine whether the valve body is flexible and the cylinder is well sealed by manually operating the pneumatic valve.If the water in the air source zone is controlled to block the filter pressure reducing valve, the compressor will be frequently loaded and unloaded due to the inability to control the switch valve.In view of this situation, the sampling point of control air source can be changed to the outlet pipe of the cold dryer to solve the problem of control air source water.

3) if the temperature of the precooler and evaporator in the cold dryer is not well regulated, it is easy to cause most of the inlet and outlet of the evaporator to block ice, thus preventing the flow of gas.It can be judged by the observation method that the ice block occurs or the evaporator temperature is not adjusted properly.Or the parameter setting of the cold dryer does not meet the design requirements of the equipment, should be adjusted in time, so as to avoid the unnecessary loss caused by freezing damage to the equipment.This kind of situation happens more in the period of seasonal change.

4) the improper installation of the outlet one-way valve of the dust filter or the shedding of the valve stem and valve body will also lead to frequent loading and unloading of the compressor.The above factory once put the valve in the wrong direction after inspecting the leakage defect in the outlet one-way valve of the dust filter, resulting in that the compressed air could not flow into the gas storage tank, while the gas in the gas storage tank could flow back to the cold dryer, resulting in frequent loading and unloading of the unit.

3. Unstable gas consumption leads to frequent loading and unloading

In this case, the method of adding gas storage tank is generally adopted, or the volume of the original gas storage tank is increased.If the installation of gas storage tank can not meet the production needs, it is recommended to use variable frequency compressor to replace the original power frequency unit.Besides solving the harm caused by frequent loading and unloading, variable frequency compressor has some other advantages:

(1) stable air pressure

Because the variable frequency screw compressor generally USES the inverter stepless speed regulation characteristics, through the controller or inverter internal PID regulator, can gently start;On the occasion of large fluctuation of gas consumption, it can quickly adjust the response.

Compared with the upper and lower switching control of power frequency operation, the air pressure stability is improved exponentially.

(2) start without impact

Because the inverter itself contains the function of the soft starter, the maximum starting current is within 1.2 times of the rated current, and the power frequency starting is generally more than 6 times of the rated current, the starting impact is very small.This impact is not only to the power grid, the impact on the entire mechanical system, but also greatly reduced.

(3) variable flow control

The compressor driven by power frequency can only work in one discharge capacity, and the variable frequency compressor can work in a wide range of discharge capacity.Inverter is based on the actual gas consumption of real-time adjustment of motor speed, to control the exhaust.When the gas consumption is low, the compressor can be automatically dormant, which greatly reduces the energy loss.

(4) the voltage adaptability of ac power supply is better

The inverter with over-modulation technology can still output enough torque to drive the motor when the ac power voltage is slightly lower.When the voltage is slightly higher, the output voltage to the motor will not be higher.For the occasion of spontaneous electricity, variable frequency drive can show its advantages.

(5) low noise

Most working conditions of the frequency conversion system are lower than the rated speed of operation, the main machine mechanical noise and wear down, extend 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.Only insist on regular inspection and timely replacement of the relevant parts, to ensure the normal mechanical work, so as to ensure the continuity of enterprise production, stability, bring higher benefits for the enterprise.



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