Compressor problem causes analysis and measures

Compressor is a machine used to increase gas pressure and transport gas. From an energy point of view, a compressor is a machine that converts the power energy of the prime mover into gas pressure energy. With the development of science and technology, the application of pressure energy has become increasingly widespread, making compressors one of the indispensable key equipment in many sectors of the national economy. During the operation of the compressor, some malfunctions and even accidents will inevitably occur. A fault refers to an abnormal situation that occurs during the operation of the compressor. Once eliminated, the compressor can resume normal operation, while an accident refers to a damage situation. The two are often related, and if a fault is not eliminated in time, it will cause a major accident. Common faults, their causes and measures
Insufficient discharge volume: Insufficient discharge volume is compared with the design air volume of the compressor. It can be mainly considered from the following aspects:
. Failure of the air intake filter: scale accumulation and blockage reduce the exhaust volume; the suction pipe is too long and the diameter is too small, resulting in increased suction resistance and affecting the air volume. The filter must be cleaned regularly.
2. Reducing the compressor speed reduces the exhaust volume: the air compressor is used improperly, because the exhaust volume of the air compressor is designed according to a certain altitude, suction temperature, and humidity. When it is used at a temperature exceeding the above standards When on a plateau, the suction pressure decreases, etc., and the exhaust volume inevitably decreases.
3. The cylinder, piston and piston ring are severely worn and out of tolerance, which increases the relevant gaps and leakage, affecting the exhaust volume. During normal wear, wearing parts such as piston rings need to be replaced in time. If the installation is incorrect and the gap is not appropriate, it should be corrected according to the drawing. If there is no drawing, empirical data can be used. For the gap along the circumference between the piston and the cylinder, if it is a cast iron piston, the gap value is the diameter of the cylinder. 0.06/00～0.09/00; for cnc machining aluminum alloy piston, the clearance is 0.2/00～0.8/00 of the gas diameter; for steel piston, the smaller value of aluminum alloy piston can be used.
4. The stuffing box is not tight enough to cause air leakage and reduce the air volume. The first reason is that the stuffing box itself does not meet the requirements when it is manufactured; secondly, it may be that the center of the piston rod and the stuffing box is not properly aligned during installation, causing wear, strain, etc., causing air leakage; generally, lubricating oil is added to the stuffing box. , which plays the role of lubrication, sealing and cooling.
5. The impact of compressor suction and exhaust valve failures on exhaust volume. Metal fragments or other debris fall between the valve seat and the valve plate, causing the valve to not close tightly, causing air leakage. This not only affects the exhaust volume, but also affects the changes in interstage pressure and temperature; the loose contact between the valve seat and the valve disc causes air leakage, which affects the exhaust volume. One is manufacturing quality problems, such as valve disc warpage, etc. The second is air leakage due to severe wear of the valve seat and valve plate.
6. The valve spring force does not match well with the gas force. If the elastic force is too strong, the valve plate will open slowly, and if the elastic force is too weak, the valve plate will not close in time. These not only affect the air volume, but also affect the increase in power and the life of the valve plate and spring. At the same time, it will also affect changes in gas pressure and temperature.
7. The pressing force of the air valve is improper. If the pressing force is small, air will leak. Of course, if it is too tight, it will deform and damage the valve cover. Generally, the pressing force can be calculated by the following formula: p=kπ/4 D2P2, D is the diameter of the valve cavity, and P2 is the maximum gas. Pressure, K is the value greater than, generally .5~2.5, K=.5~2.0 at low pressure, K=.5~2.5 at high pressure. Taking K in this way has been proved to be good in practice. If the air valve is faulty, the valve cover will inevitably become hot and the pressure will be abnormal.
Abnormal exhaust temperature means that the exhaust temperature is higher than the design value. Theoretically, the factors that affect the increase in exhaust temperature include: intake air temperature, pressure ratio, and compression index (for air compression index K=.4). The actual factors that affect the high suction temperature are: low intercooling efficiency, or excessive scale formation in the intercooler that affects heat transfer. Then the suction temperature of the subsequent stages must be high, and the exhaust temperature will also be high. Air valve leakage and piston ring leakage not only affect the increase in exhaust temperature, but also cause inter-stage pressure changes. As long as the pressure ratio is higher than the normal value, the exhaust temperature will increase. In addition, for water-cooled machines, lack of water or insufficient water volume will increase the exhaust temperature.
If the pressure is abnormal and the exhaust pressure is reduced, the air volume discharged by the compressor cannot meet the user’s flow requirements at rated pressure, so the exhaust pressure must be reduced. The required exhaust pressure decrease is a phenomenon, and its essence is that the exhaust volume cannot meet the user’s flow requirements. the request of the person. At this time, we have to change to another machine with the same exhaust pressure and larger exhaust volume. The main cause of abnormal interstage pressure is air valve leakage or piston ring wear and leakage, so the causes should be found and measures should be taken from these aspects.
Abnormal sound If some parts of the compressor fail, it will make abnormal sounds. Generally speaking, the operator can identify the abnormal sounds. The gap between the piston and the cylinder head is too small, causing direct impact; the connecting nut between the piston rod and the piston is loose or tripped, the end face of the piston is blocked, the piston moves upward and collides with the cylinder head, metal fragments fall into the cylinder, and moisture accumulates in the cylinder, etc. All can make a knocking sound in the cylinder. The crankshaft bolts, nuts, connecting rod bolts, and cross-head bolts in the crankcase are loose, tripped, broken, etc., the shaft diameter is seriously worn and the gap increases, the cross-head pin and bushing clearance is too large or severely worn, etc. A banging sound is heard in the crankcase. The exhaust valve piece is broken, the valve spring is loose or damaged, the load regulator is improperly adjusted, etc., which can cause knocking sounds in the valve cavity. From this, faults can be found and measures taken.
Overheating failure occurs at the friction points between the crankshaft and bearings, crosshead and supply mirror uv plate, packing and piston rod, etc. If the temperature exceeds the specified value, it is called overheating. The consequences of overheating: one is to accelerate the wear between the friction pairs; the other is that the heat of the overheating continues to accumulate until the friction surface is burned and the lock is burned, causing major machine accidents. The main causes of bearing overheating are: uneven fit between the bearing and the journal or too small contact area; deflection of the bearing, bent crankshaft, too low viscosity of lubricating oil, blockage of the oil circuit, failure of the oil pump, etc.; no leveling during installation. , the gap is not found, the spindle and the motor shaft are not aligned, the two axes are tilted, etc.
Compressor accident
Fracture accident Crankshaft fracture: Most of the fractures occur at the transition of the fillet between the journal and the crank arm. The reasons are generally as follows: the transition fillet is too small, r<0.06d (d is the crankshaft neck); during heat treatment, the fillet The corners are not handled properly, resulting in stress concentration at the junction; the fillet processing is irregular and there are local cross-sectional mutations; long-term overload operation, and some users increase the rotation speed casually in order to increase output, worsening the stress condition; the material itself is defective , such as castings with blisters, shrinkage porosity, etc. In addition, cracks in the oil hole on the crankshaft causing breakage can also be seen.
Breakage of the connecting rod: There are several situations: the connecting rod screw breaks. The reasons include: plastic deformation of the connecting rod screw due to long-term use; poor contact between the screw head or nut and the big head end surface, resulting in eccentric load, which can be so large that the bolt is It is as much as seven times the pure axial tension. Therefore, no slight skew is allowed, the contact should be evenly distributed, and the maximum distance between the contact points should not exceed /8 of the circumference, which is 450; there is a problem with the processing quality of the bolt material.
Piston rod fracture: The main fracture parts are the thread connecting the crosshead and the thread fastening the piston. These two places are the weak links of the piston rod. If it is due to negligence in design, sloppiness in manufacturing and operation reasons, , fracture occurs more frequently. If there are no problems in design, processing, and materials, the preload force must not be too large during installation, otherwise the piston rod will break when the maximum force reaches the yield limit. After long-term operation, due to excessive wear of the cylinder, the piston in the horizontal row will sink, causing additional load on the connecting thread. If the operation continues, the piston rod may break. This should be paid special attention to during maintenance. In addition, when the piston rod is subject to a strong impact due to damage to other parts, the piston rod may break.
Cylinder and cylinder head rupture: Main reason: For water-cooled machines, if you forget to drain all the cooling water in the cylinder and cylinder head after running and stopping in winter, the cooling water will freeze and burst the cylinder and cylinder head, especially in In the northern region of our country, the cooling water must be drained after parking; because the water was interrupted during operation and was not discovered in time, the temperature of the cylinder increased, and cooling water was suddenly added, causing the cylinder to explode; because the dead center gap was too small, the piston Loose nuts, metal objects falling into the cylinder, and the plugs on the piston coming out will cause the piston to hit the cylinder head and cause it to break.
Combustion and explosion accidents often cause carbon deposits in oil-lubricated compressors, which we do not want, because carbon deposits will not only cause the piston rings to get stuck in the grooves, but also cause the air valve to work abnormally and reduce the area of the air flow channel. resistance, and under certain conditions, carbon deposits will burn, causing the compressor to explode. Therefore, the lubricating oil in the cylinder cannot be supplied too much, and gas that is not well filtered and contains a large amount of dust cannot be sucked into the cylinder, otherwise carbon deposits will form and contact with gas containing a large amount of volatile matter will cause an explosion. In order to prevent combustion and explosion, it is necessary to plan maintenance and regularly clean the grease in the gas storage tank and pipelines.
In addition, there are the following operational reasons for compressor combustion and explosion accidents: before the compressor is tested with hydrogen, oxygen, and nitrogen loads, low-pressure nitrogen is not used to purge the air, causing an explosion. Due to lack of operating knowledge, the valve from the compressor to the gas tank was not opened after driving, causing the exhaust pressure to rise sharply and cause an explosion. Therefore, to prevent such accidents from happening, you must be familiar with the operating procedures before driving, and pay close attention to the pressure gauge value after driving. In general small and medium-sized compressors, it is best to cancel the gate valve on the pipeline from the compressor to the gas storage tank, leaving only the check valve. In addition, compressor operators should receive pre-job training.
Because the high-pressure stage valve of the compressor is not tight, the high-pressure and high-temperature gas returns to the cylinder and generates high temperature near the exhaust valve. When there is carbon deposit, it will cause an explosion. In order to avoid accidents, it is necessary to repair the exhaust valve, check the leakage part, and eliminate the fault at this time.