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ACparts Engineering Sdn Bhd
ACparts Engineering Sdn Bhd (902639-U)
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Air compressor "jump" failure, analyze the reasons and how to deal with it!

30-Jun-2022

Troubleshooting of Air Compressor ''Jump''


The so-called air compressor tripping usually refers to the compressor outage caused by the overload of the compressor and the disconnection of the protector.
 
Usually, except for the ''tripping'' fault caused by the external power supply, which is not the cause of the air compressor itself and does not need to be dealt with, the ''tripping'' fault caused by the tripping of other overload protectors must be treated with care, and the consequences of forced operation may cause the unit to be scrapped.
 
There are various reasons for the flight jump, the most common one being the high temperature ''jump flight'', especially in Malaysia, where the temperature is relatively high. To deal with high-temperature tripping, it must start with reducing the operating temperature of the unit.
 

The ''exclusion method'' can be adopted to rule out the causes of the failure one by one.

1. Pressurized starting 

''Starting with pressure'' means that the back pressure of the compressor is too high when the air compressor starts.
 
Check the mechanical pressure gauge on the oil and gas barrel of the compressor on site. If the pressure gauge shows pressure, it is preliminarily determined that the system may not be fully depressurized, causing the compressor to start under pressure. Causes the starting current to be too high to cause the air switch to trip to protect the unit.
 
In screw air compressors, there is often a phenomenon that pressure still exists in the system after the compressor shuts down due to the failure of the minimum pressure valve or the blockage of the pressure relief system.
 
On-site inspection of the pressure gauge shows that there is pressure. Generally, there are two possibilities:
 
     First, there is indeed pressure in the system;
 
     The second is that the pressure gauge is damaged and cannot be reset to zero normally.
 
The method of judgment is to open the device or valve in the system that can relieve pressure. When the pressure relief valve is opened and the pressure gauge in the oil and gas barrel shows that there is still pressure, it is judged that there is no pressure in the system because the pressure gauge cannot be reset to zero; otherwise, the system is under pressure.


 

2. The resistance of the machine head is too large


If the resistance of the machine head is too large, the starting current of the compressor will be too large, that is, the compressor is overloaded, causing the air switch to trip.
 
Three main situations lead to increased nose resistance:
(1) The viscosity of lubricating oil is high. The temperature in the southern region varies greatly with the seasons, and the ambient temperature in summer can reach as high as about 40 ℃


(2) For single-screw compressors, the screw and star wheel in the head are coked. The work of the single-screw compressor is mainly completed by the meshing of the screw and the star wheel. The size of 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 gas leaks from the gap, and the compressor's work efficiency is low; if the gap 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. Coking is the machine head can reduce the gap between the star wheel and the screw, the friction resistance in the meshing is large, and the current of the compressor increases.
 
(3) The amount of lubricating oil in the machine head is too much. The oil shut-off valve at the outlet of the machine head is faulty. After the compressor is stopped, the oil shut-off valve is not closed in time, and a large amount of lubricating oil is pressed into the machine head. machine''.
 

How to handle:

(1) Manual cranking is the most basic detection method for the connection and free rotation of the compressor power components, transmission components, and linkage components. Through manual cranking of the compressor before starting, it is checked whether the machine head and the motor can rotate freely and whether the resistance of the rotation increases or not is determined according to the previous cranking experience.
 
(2) Oil coking in the nose is a phenomenon that often occurs in screw compressors when the oil is poor or the temperature is high. Due to the coking of the nose, the gap between the screws or between the screws and the star wheel becomes smaller. During the process, the frictional resistance increases, the load of the unit increases, and the current increases. In severe cases, the screw and the star wheel are glued together by an oil coke, and the unit cannot rotate freely.
 
(3) The function of the oil cut-off valve on the oil injection pipe of the machine head 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 machine head due to the residual pressure in the oil and gas barrel, resulting in excessive lubricating oil in the machine head. many. Therefore, too much lubricating oil in the machine head after shutdown is also one of the reasons for the large starting current of the compressor. The most direct way to solve the problem of too much lubricating oil in the machine head is to open the end cover of the machine head, release part of the lubricating oil in the machine head, and repair or replace the oil shut-off valve at the same time.


 

3. Failure of electrical equipment

Many users use 380V motors, which are started by the star-delta conversion step-down starting method. In the early stage, it runs in star mode, and after 2~3s of a startup, it changes to delta mode. If the star-delta transfer switch fails, normal star-delta conversion cannot be performed, the star-shaped current is many times higher than the delta operating current, and the protector delay time expires, which will naturally cause the compressor to trip. In addition, due to vibration and other reasons during the use of the air switch, the set start-up time is shortened, which may also lead to ''jumping'' at the moment of start-up.
 
The most direct and effective way to judge whether it is an electrical fault or a mechanical fault is to separate the motor from the head, that is, to remove the coupling or belt connected to the head. Manually crank the compressor unit and motor separately to rule out mechanical problems.
 
If it is caused by the mechanical reasons of the compressor head and the motor, the motor can run normally when the load is thrown off and the motor can run normally; otherwise, it is a problem with the electrical part.
 
But please note that some of the faults are caused by the motor itself. It feels normal when the motor is manually turned, and the motor behaves normally when it is started with no load. Once the load is loaded, the problem of overload ''jumping'' occurs. This problem is generally the motor bearing. Or caused by the misalignment of the connection between the motor and the compressor host.
 
In the actual production operation, there is another reason for the tripping, although it is relatively rare, it also exists. Electronic control system faults, such as false alarms of temperature probes, ultra-high temperature trips, and alarms caused by faulty actions of temperature relays and circuit breakers in high-temperature environments.


4. Failure of the unloading valve

The unloading valve is an important part of the screw compressor. Its main function is to control the loading and unloading of the unit, that is, to control the air intake of the compressor.
 
Early opening of the unloading valve is a kind of fault that is not easy to find. The unloading valve of the compressor is closed before starting, and the unloading valve is also opened slowly during the starting process, or it is fully opened after starting. If the unloading valve is opened too early, it means that the load of the compressor is too large when it starts, increasing the starting current of the compressor, and causing the compressor to ''jump''.
 
The most intuitive way to judge whether the unloading valve is closed is to remove the air filter, and you can see whether the intake baffle of the unloading valve is closed or open.
 
Most unload valve failures are when the intake flapper is stuck on the guide rod, and the position of the piston at this time should cause the intake flapper to close, but the unloading valve cannot be closed because the intake flapper is stuck. In addition, there are also cases where the unloading valve intake baffle is stuck by foreign objects such as mechanical impurities, resulting in the unloading valve not being fully closed.
 
After removing the air filter, if the intake baffle is stuck due to mechanical impurities, etc., the unit can be turned on smoothly after cleaning; Apply a small amount of grease on it; if the unloading valve is seriously damaged, the unloading valve needs to be replaced.
 
To judge whether the unloading valve is opened in advance, it is necessary to accurately grasp the start-up time of this type of compressor, and at the same time, according to the time when the unloading valve is opened and the compressor start-up time, if the former is greater than the latter, it proves that the unloading valve does not It is not opened in advance; on the contrary, the unloading valve is opened in advance.


 

5. High-temperature trip caused by thermostatic valve


Some high-temperature trips are not caused by external temperature or poor heat dissipation of the unit, but by poor operation of the temperature control valve.
 
There is a temperature-sensing component (usually paraffin) in the temperature-controlled bypass valve, and the probe of this component controls the on-off of the valve core. After long-term use, the efficiency of the valve core is reduced, and it cannot operate at the corresponding temperature point so that the hot lubricating oil from the air compressor body cannot or all be cooled by the oil cooler and directly return to the air compressor body so that the temperature of the air compressor cannot 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 cannot be completely closed, and some oil is directly bypassed to the machine, and the cooling effect is not good.
 

6. High-temperature trip due to lubricating oil


Lubricating cooling oil failed. The lubricating oil of the air compressor not only lubricates the moving parts, such as the rotor and the vane that rotate at high speed. Moreover, a large amount of heat energy is generated during the cooling and compression process, such as friction heat generated by the relatively high-speed motion of the friction pair and heat energy generated when the air is compressed.
 
The air to be compressed contains a large amount of dust, water, and corrosive hydrogen fluoride and sulfur dioxide gas, which has a great impact on the lubricating oil and makes the lubricating oil ineffective. After the lubricating oil fails, the oil film is not formed on the relative motion pair, the heat generated by the relative motion friction increases, and the cooling effect decreases, which makes the temperature rise of the air compressor too high during operation.
 
In addition, the characteristics of high temperature ''jumping'' caused by faults in air coolers, water coolers, and three filters are more obvious, so I won't repeat them.
 
In short, there are many reasons for compressor tripping, and there are many reasons for it. Only when we have a more comprehensive understanding of the operating principle of the compressor and the function of its components, can we prevent the tripping failure of the compressor before it happens.
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