Jinan screw air compressor often loads and unloads, what's wrong? "Screw air compressor often loading and unloading" is a kind of special faults, for customers or some industry novices, it is not even known. Some children asked about it, so it's written. What's missing please Haihan.
This kind of fault, the unit controller itself does not have any fault hints, air compressor start-up and shut-down operation, the various electrical parameters seem to be normal. In some "big horse trolley" air compressor margin comparable to a large number of gas conditions, the use of gas end also feel no abnormality. Unlike other faults, it has a very intuitive performance, strong shade, but great harm.
So what is the manifestation of this defect?
The literal meaning of "frequent loading and unloading" is that the distance between loading and unloading of screw air compressor is very short, and this cycle is frequent. How short is the time? From a few seconds to a dozen seconds, you can think it's frequent.
Faults: Lower than the loading pressure air compressor start loading and exhaust pressure rise speed a few seconds to more than ten seconds to reach the set unloading pressure air compressor unloading stop exhaust pressure drop speed a few seconds to more than ten seconds pressure drop to the set loading pressure air compressor start loading exhaust such a cycle to and fro.
Harm of frequent loading and unloading of air compressor无须置疑，此种毛病对空压机的危害极为严重的，主要是：
Undoubtedly, this kind of defect is extremely harmful to the air compressor, mainly:
The life of moving parts touched by loading and unloading of air compressors will be greatly shortened, such as intake valves and their valves, minimum pressure valves, relief valves, etc., which will lead to more other problems. Although frequent loading and unloading start and stop frequently, the impulse of motor and main engine is not so great, but the frequent alternation of light and heavy loads and the frequency of smooth conditions. The bearing damage of motors and main engines is very obvious because of various changes. 3. The impact of frequent loading and unloading on the filtration installation of gas and oil circuits will lead to the early failure of oil core separation and oil filtration. 4. With the increase of power consumption, the possible causes of frequent loading and unloading of air compressors with very low unit energy efficiency and the analysis should first remove some of the foolish elements:
There is no gas storage tank or minimal gas storage tank, the air compressor exhaust volume is large and the gas consumption is small; 2) the gas consumption is large when single gas is used, but there is not enough buffer gas storage tank; 3) the pressure setting of loading and unloading is too close, such as loading 6.9 bar, unloading 7.0 bar; secondly, understand the control principle of screw machine loading and unloading:
The control logic of screw air compressor loading and unloading is to trigger loading and unloading action by setting pressure value, such as 6bar loading and 7bar unloading. It is different from the mechanical structure of pressure switch of small piston machine. Screw machine monitors pressure through pressure transmitter. Pressure transmitter provides electric signal of 5~20mA of controller. The controller stops conversion and discrimination again, and outputs electric signal to control various solenoid valves for loading and unloading.
The sampling point of pressure transmitter of screw machine is usually set at the exhaust port of screw machine after the air cooler. The exhaust port of the screw machine is connected with the pipe network, and ensuring that the pressure of the pipe network is not less than the requested pressure is the sole purpose of the work of the air compressor. Therefore, when the pressure sampling point monitors that the pressure is equal to or lower than the set loading pressure, the air compressor must be loaded. On the contrary, when the pressure is equal to or higher than the set maximum pressure, the air compressor must be unloaded.
Loading and executing actions of air compressor are: air compressor intake valve is opened, a large amount of air is intake, through contraction, separation, top-opening the minimum pressure valve, cooling and discharging to the trachea network; unloading action of air compressor is: the intake valve is closed, only a small amount of air is intake, the relief valve action relieves internal pressure (that is, the pressure in the air path before releasing the minimum pressure valve, generally only saves the oil cycle needs. Pressure, unloading time of oil and gas barrel pressure is generally only 2 bars more, in order to re-load only accept lower back pressure, reduce energy consumption, the minimum pressure valve at this time plays a key one-way check role, do not allow waste products in the pipeline to tighten gas back flow to the oil and gas barrel to be released.
Through the analysis of the above principles, it can be seen that the loading and unloading of screw air compressor depends on the pressure change at the pressure sampling point, then the following causes of frequent loading and unloading of air compressor are easy to understand:
Whether there is a check valve between the air compressor outlet and the gas storage tank?
This point, in all screw machine training, it is clear that the request should not install check valves. This is due to the piston machine period, the device check valve is standard operation, some "teachers" and even the design institute, up to now there are still such designs. Understand a point: It is not that the screw machine must start frequently when the check valve is installed, which is related to the sealing of the minimum pressure valve of the screw machine. If the minimum pressure valve is well sealed, frequent starting is not obvious. Ideally, however, most minimum pressure valves are virtually impossible to seal.
If a check valve is installed between the air compressor and the storage tank, it means that the pipeline between the minimum pressure valve and the check valve of the air compressor will constitute a de facto storage space. In this way, pressure sampling points can not monitor the pressure changes in the pipeline network (check valves cut off the return flow of the pipeline, and the pressure transmitter actually monitors only the pressure of the gas in this section of the pipeline).
When the unit is unloaded, the pressure of this section of pipeline is higher than that in the oil and gas barrel (as mentioned above, the pressure of the oil and gas barrel is released, only about 2 bars), and the minimum pressure valve can not achieve complete check seal, it will inevitably leak to the oil and gas barrel, plus the volume cost of this section of pipeline is very small, the pressure will be reduced quickly due to leakage (so check valve). The closer to the exhaust outlet of the air compressor, the more obvious the frequent loading and unloading. The closer the exhaust outlet is, the smaller the volume of the pipeline is.
When the barrel pressure reaches the minimum opening pressure of the pressure valve, the air flow moves to the pipeline network through air cooling, and the pressure of the pipeline where the pressure changer is located is rapidly increased until the top check valve is connected with the pipeline of the pipeline network. Perhaps at this time, the pressure of the pipeline network is only slightly lower, and the natural pressure will soon reach discharge. Loading pressure and unloading action are the reasons for frequent loading and unloading of screw machines.
If the output of the air compressor is greater than the air consumption, if the air compressor and the air consumption are equal or the pressure can not be filled, the phenomenon of frequent loading and unloading will not occur. That is to say, the unloading pressure can not be reached by the continuous loading of the air compressor, but this situation will not occur. Therefore, this situation does not exist in frequency conversion and some air compressors with capacitive power regulation function, that is, it will not occur without unloading discharge. However, in any case, it is harmful and unhelpful to install a check valve in the back of the screw machine.
When no check valve is found in the device, why is this phenomenon?
After the reasons of frequent loading and unloading of check valves in the above devices, divergent thinking shows that all other reasons that may cause the blockade of pipelines in the left and near parts of pressure sampling points may cause the occurrence of this situation.
For example, if the outlet of the air compressor is connected with a filter, if the filter is blocked or seriously blistered (air flow can pass through, only enough back pressure is needed), it is easy for the air compressor to reach the set upper pressure limit at the pipeline (pressure sampling point here) where the air compressor passes through the filter, and then unload the air compressor and practice the pressure of the main pipe network. It's bound to arrive. The high-pressure air in this section of the pipeline continues to move toward the two low-pressure ends (through filters to the pipeline network, minimum pressure valve to the oil and gas barrel). As mentioned above, because of the small volume of the pipeline, the pressure will drop rapidly in a very short time.
As a result, the air compressor outlet is connected with a smaller pipeline, there is a lot of water in the storage tank, and some sundries in the pipeline happen to constitute a check effect, which may form this situation. Of course, there are other examples of pressure transmitter pressure sampling tube water may also present similar problems.
Finally, the defect maintenance of screw air compressor requires more understanding of its principle and the mechanism of defect composition. Even if we lack experience, we can not quickly locate the problem, but as long as the direction is good, after wire pulling and cocoon stripping, coupled with courage and meticulousness, there will be no problem that can not be handled.