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The reason and treatment method for air compressor jumping

Time: 2022-08-23 13:15:38

Usually referred to as the air compressor jump, refers to the compressor overload protector being disconnected, resulting in compressor shutdown. Generally, the recovery time after the overload protector jumps open is long, and the compressor can not be used normally at this time. There are a variety of reasons for air compressor jumping, the most common is high-temperature jump, especially in the summer with high temperature, but there are also some other common reasons, maintenance has certain difficulty. Unfamiliar after-sales maintenance personnel will feel more comfortable when encountering such problems.

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Through this article, we can take the reason and treatment method for air compressor jumping:

  1. Start with pressure 

Check the pressure gauge on the oil and gas tank of the compressor on site. If the pressure gauge shows pressure, it is preliminarily determined that the system may not be completely relieved. As a result, the compressor starts with pressure, and the starting current is too high, which causes the air switch to trip to protect the unit. Because in the screw air compressor often appear due to MPV failure, or pressure relief system blockage caused by compressor shutdown, there is still pressure in the system.

The pressure gauge shows pressure, in general, there are two possibilities: one is that there is pressure in the system; Second, the pressure gauge damage, can not return to zero normally. The method of judgment is to open the device or valve that can relieve pressure in the system. When the pressure gauge in the oil and gas tank is found to still have pressure after opening the safety valve, it is judged that the system has no pressure, which is caused by the pressure gauge can not return to zero. Otherwise, it is the system with pressure. This is the main reason for air compressor jumping.

  1. Air end resistance is too large 

If the air end resistance is too high, the compressor will be overloaded and the air switch will trip. The role of lubricating oil in screw compressor is very important, its role is mainly manifested in four aspects: cooling, lubrication, sealing, noise reduction, and the quality of oil, the amount of oil directly affects the normal operation of the compressor and the service life of the compressor, especially the air end part of the compressor is most obvious. Three main situations lead to the increase in nose resistance: 

(1) High viscosity of lubricating oil. The temperature in the south varies greatly with the seasons. The ambient temperature in summer can be as high as about 40 ℃, and the temperature in winter can be as low as below zero. According to the characteristic that the viscosity of general lubricating oil is inversely proportional to the temperature, the viscosity of lubricating oil is significantly higher than before. Commonly used several kinds of lubricating oil viscosity and temperature characteristics curve.

(2) Coke of screw and star wheel in the air end (single screw compressor). The work of the screw compressor is mainly completed by the meshing of the screw and the star wheel. The gap between the screw and the star wheel determines the work efficiency of the compressor. If the gap is too large, part of the air leakage from the gap, and the compressor work efficiency is low; If the clearance is too small, the resistance between the star wheel and the screw is large, the load is large, and the energy consumption of the motor is large. The coke in the air end can lead to the gap between the star wheel and the screw being reduced, the friction resistance in the meshing is large, the current of the compressor is increased, and the twin screw is the same.

(3) the amount of lubricating oil in the air end is excessive. The air end outlet oil break valve is faulty. After the compressor is shut down, the oil break valve is not closed in time, and a large amount of lubricating oil is pressed into the nose, which causes the starting resistance to be large in the starting process, and the increase of current leads to the overload protection cause air compressor jumping.

The processing methods are as follows: 

(1) Manual turning is the basic test method for the connection and free rotation of the compressor power parts, transmission parts, and linkage parts. Through the manual turning of the compressor, to check whether the air end and motor can rotate freely, and according to the previous turning, experience to determine whether the resistance to rotation increases. When the ambient temperature is lower (the ambient temperature at that time can be judged from the exhaust port temperature displayed by the unit), the resistance may be because the temperature is reduced, and the viscosity of the oil increases. As the viscosity of lubricating oil in the nose increases, the starting current of the motor becomes larger and the starting time of the compressor is prolonged. The start time of the motor on the air switch can be slightly extended under the condition of ensuring safety (too much extension may lead to a higher level of air switch jumping, thus affecting other electrical equipment) to meet the extension of the start time of the compressor when the oil viscosity increases, to ensure the normal start of the compressor.

(2) the oil coking in the air end is a common phenomenon of screw compressors in the case of poor oil or high temperature. Because of the air end coking, the gap between the screw and the star wheel becomes smaller, and the friction resistance increases in the process of rotation, the load of the unit increases, and the current increases. When the screw and the star wheel are glued together by oil coke, the unit can not rotate freely.

(3) The function of the oil breaking valve on the oil injection pipe of the air end is to cut off the oil injection pipe in time when the unit is shut down, to prevent a large amount of lubricating oil from being pressed into the air end due to the excess pressure in the oil and gas tank, resulting in too much lubricating oil in the air end. Therefore, too much lubricating oil in the air end after shutdown is also one of the reasons for the compressor starting current being too big. The direct way to solve the problem of excessive lubricating oil in the air end is to open the end cover of the nose, release part of the lubricating oil in the air end, and repair or replace the oil breaking valve at the same time.

  1. Electrical device failure 

Many users use 380V low-voltage motor, which is started by star-triangle conversion step-down starting mode. In the early stage, the compressor is operated in star mode, and then it will be operated in triangle mode after starting for 10 s. If the star delta transfer switch is faulty, the normal star delta transfer cannot be performed, this is one of the reasons for the air compressor jumping 10s after starting. In addition, the air switch in the process of use due to vibration and other reasons, resulting in its set start time being shorter may also lead to starting instant jump.

The direct and effective way to determine whether it is an electrical or mechanical fault is to separate the motor from the air end, that is, remove the coupling/belt. The control system of the compressor is equipped with a protection device. If the protection device is not separated and the compressor is started, the motor will run immediately. The motor current will be displayed on the control panel as about 40A, and an abnormal current will be displayed after running for 10 s. Because when the current is detected to be greater than 10% of the max current or less than 90% of the min current, the protection unit will automatically stop, so it will not be able to judge the fault cause of the unit. When the protection is thrown off, the motor will run continuously for mechanical reasons; Otherwise, there will be the same trip phenomenon.

In real production, there is another reason for air compressor jumping, although relatively rare, also exist. Electric control system faults, such as temperature probe false alarm, temperature relay, and circuit breaker malfunction in high-temperature environments caused by ultra-high temperature jump stop and alarm. If some compressor power board with the original due to various reasons caused by damage, work slowly generate heat, part of it is distributed to the outside air, part of the transfer to the control computer. The power supply board is installed in the electric control cabinet of the compressor. There is a large vibration during the operation of the equipment, which to some extent speeds up the heat emission of the capacitor. The heat generated by the capacitor cannot be transmitted to the control computer stably, thus causing frequent fluctuations in the exhaust temperature of the host on the display. Over time, the capacitors generate more and more heat, the sensors conduct more and more heat, and when the upper temperature set in the control computer is reached, the machine automatically jumps. The temperature transferred to the sensor by the capacitor is different from the value of heat generated and the value of emission, so the sensor transfer temperature rise is different. When the high-temperature alarm jumps, the capacitor temperature is lost, and the heat is generated again. After a fixed time, the machine jumps, resulting in repeated high-temperature jumps.

  1. The unloading valve is faulty 

The unloading valve is an important part of the screw compressor, its main role is to control the loading and unloading of the unit, that is, to control the compressor intake.

The most intuitive way to judge whether the unloading valve is closed or not is to remove the air filter, and you can see whether the inlet baffle of the unloading valve is in the closed or open state. Most discharge valve failures OCCUR when the intake baffle is stuck to the guide rod, and the piston is in a position that should close the intake baffle, but cannot close the discharge valve because the intake baffle is stuck. In addition, there are cases where the inlet baffle of the unloading valve is stuck by foreign bodies such as mechanical impurities, resulting in the incomplete closure of the unloading valve. After removing the air filter, if the inlet baffle is stuck due to mechanical impurities, the unit can be opened smoothly after cleaning; If the inlet baffle is stuck on the guide rod, grind the guide rod with sandpaper, and apply a small amount of grease on the guide rod; If the unloading valve is seriously damaged, the unloading valve needs to be replaced.

Unloading valve opened ahead of it is not easy to find fault, because before the start of the unloading valve is closed, and in the process of starting unloading valve is also slowly open, just open, earlier than the unit set of time may only open for a few seconds in advance, but could cause compressor starting current increases, the compressor trip. Cause of unloading valve opened ahead of time is used to control the valve on the motion of the piston rod and guide bar spring elastic decrescent, the signaling load control system did not give unloading valve, inlet damper under the action of vacuum negative pressure in the air end sucked away, namely the compressor load in advance, the unit is not yet in full swing, so that the motor has been in high current, cannot to convert the star triangle, Cause the air switch to trip. To judge whether the unloading valve is opened in advance, it is necessary to accurately master the starting time of this kind of compressor. At the same time, according to the opening time of the unloading valve and the starting time of the compressor, if the former is greater than the latter, the unloading valve is not opened in advance. On the contrary, the unloading valve opens in advance.

  1. lubricating oil caused high-temperature jump machine 

There is a temperature sensing probe on the sliding spool of the temperature control bypass valve, which controls the on-off of the spool by the probe, and determines the opening temperature of the temperature control bypass valve at 70± Within 10 ℃. After long-term use, the efficacy of the probe is reduced and it can not act at the normal temperature point so that the hot lubricating oil coming out of the air compressor body can not or all be cooled by the oil cooler directly back to the air compressor body so that the temperature of the air compressor can not be effectively controlled.

When the lubricating oil with impurities passes through the temperature control valve, the sliding core is stuck, so that the valve core can not be completely closed. Some oil is directly passed to the machine by bypass, and the cooling effect is not good.

The oil relief valve piece falls off. The oil relief valve is to discharge too much lubricating oil from the stator cavity when the air compressor starts. If the oil pressure relief valve sheet falls off, the compressed air will enter the compression chamber for secondary compression, the air compressor load increases, and more heat is generated. The cooling system can not cool down too much heat so the air compressor temperature can not be controlled.

Lubrication cooling oil fails. The lubricating oil of the air compressor not only lubricates the moving parts, such as the high-speed rotating rotor journal and slide but also produces a lot of heat energy in the cooling and compression process, such as the friction heat generated by the relatively high-speed movement of the friction pair and the heat energy generated when the air is compressed. The air to be compressed contains a large amount of dust, moisture, and corrosive hydrogen fluoride, sulfur dioxide gas, which has a great impact on the lubricating oil and makes the lubricating oil ineffective. After lubricating oil failure, the relative motion pair does not form an oil film, the relative motion friction produces heat increase, and the cooling effect is reduced, making the temperature rise of the air compressor during operation too high.

In addition, the characteristics of high-temperature jump caused by the faults of the air cooler, water cooler, and filter are relatively obvious, so it is not mentioned here. In short, there are many reasons for air compressor jumping, induced reasons are also more, we only have a more comprehensive understanding of the principle of compressor operation and components efficacy, to nip in the bud compressor jump failure.

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