Causes of Compressor Common Failures and Countermeasures Analysis

Abstract: During the operation of the compressor, some failures and even accidents will inevitably occur. A fault refers to an abnormal condition that occurs during the operation of the compressor, which can be restored to normal operation once the compressor is eliminated, while an accident refers to a damage situation. The two are often related, and if the fault is not eliminated in time, it will cause a major accident.

   Compressor is a machine used to increase gas pressure and convey 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 essential key equipment in many sectors of the national economy. During the operation of the compressor, some failures and even accidents will inevitably occur. A fault refers to an abnormal condition that occurs during the operation of the compressor, which can be restored to normal operation once the compressor is eliminated, while an accident refers to a damage situation. The two are often related, and if the fault is not eliminated in time, it will cause a major accident.

  Common failures and their causes and measures

   Insufficient displacement:

The lack of displacement is compared with the compressor's design capacity. Mainly can be considered from the following aspects:

  1. Malfunction of the intake filter: fouling and clogging, reducing the exhaust; the intake pipe is too long and the pipe diameter is too small, resulting in an increase in the intake resistance and affecting the air volume. The filter must be cleaned regularly.

2. The reduction of the compressor speed reduces the displacement: the air compressor is not used properly, because the displacement of the air compressor is designed according to a certain altitude, suction temperature, and humidity. When it is used in excess of the above standards When on a plateau, the suction pressure decreases and the exhaust volume will inevitably decrease.

  3. The cylinder, piston, and piston ring are seriously worn and out of tolerance, which increases the clearance and leakage, which affects the displacement. When it belongs to normal grinding, the wearing parts, such as piston ring, should be replaced in time. If the installation is incorrect and the gap is not appropriate, it should be corrected according to the drawings. If there is no drawing, experience data can be taken. For the gap between the piston and the cylinder along the circumference, if it is a cast iron piston, the gap value is the diameter of the cylinder 0.06/100~0.09/100; For aluminum alloy pistons, the gap is 0.12/100~0.18/100 of the air diameter; steel pistons can take the smaller value of aluminum alloy pistons.

  4. The stuffing box is not tight and leaks and reduces the gas volume. The reason is that the stuffing box itself does not meet the requirements when it is manufactured; secondly, it may be due to poor alignment of the piston rod and the center of the stuffing box during installation, resulting in wear, strain, etc., causing air leakage; generally lubricating oil is added to the stuffing box , It plays a role of lubrication, sealing and cooling.

   5. The influence of compressor suction and discharge valve failure on the displacement. Metal fragments or other debris fall between the valve seat and the valve plate, and the closing is not tight, resulting in air leakage. This not only affects the displacement, but also affects the change of the interstage pressure and temperature; the valve seat and the valve plate are not tightly contacted to form air leakage and affect the displacement. One is the manufacturing quality problem, such as the warpage of the valve plate. The second is due to the serious wear of the valve seat and the valve plate, resulting in air leakage.

  6. ​​The spring force of the gas valve is not well matched 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. This not only affects the air volume, but also affects 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 compression force of the compression valve is improper. If the pressing force is small, the air will leak. Of course, too tight will not work, and the valve cover will be deformed and damaged. The general pressing force can be calculated by the following formula: p=kπ/4 D2P2, D is the diameter of the valve cavity, P2 is the maximum gas For pressure, K is a value greater than 1, generally 1.5 to 2.5, K = 1.5 to 2.0 at low pressure, and K = 1.5 to 2.5 at high pressure. Taking K like this has proved to be good in practice. If the air valve fails, the valve cover will inevitably heat up, and the pressure will also be abnormal.

  The exhaust temperature is abnormal

   Abnormal exhaust temperature means that it is higher than the design value. In theory, the factors that affect the increase in exhaust temperature are: intake temperature, pressure ratio, and compression index (for air compression index K = 1.4). The actual situation affects the high suction temperature factors such as: low intercooling efficiency, or excessive scale formation in the intercooler affects heat exchange, the suction temperature of the subsequent stage must be high, and the exhaust temperature will also be high. The valve leaks and the piston ring leaks, which not only affects the increase in exhaust temperature, but also changes the pressure between stages. As long as the pressure ratio is higher than the normal value, the exhaust temperature will rise. In addition, water-cooled machines, lack of water or insufficient water will increase the exhaust temperature.

  The pressure is abnormal and the exhaust pressure is reduced

  The air volume discharged by the compressor cannot meet the user's flow requirements under the rated pressure, the exhaust pressure will inevitably be reduced, and the reduction in the required exhaust pressure is a phenomenon, the essence of which is that the exhaust volume cannot meet the user's requirements. At this time, I had to replace it with another machine with the same exhaust pressure and large exhaust capacity. The main cause of abnormal interstage pressure is air valve leakage or air leakage after piston ring wear. Therefore, the reasons should be found and measures should be taken from these aspects.

   abnormal noise

   If some parts of the compressor fail, it will make an abnormal sound. Generally speaking, the operator can distinguish the abnormal sound. The gap between the piston and the cylinder head is too small, directly impacting; the piston rod and the piston connecting nut are loose or tripped, the piston end is blocked by the thread, the piston moves upward and collides with the cylinder head, metal fragments fall into the cylinder, and water accumulates in the cylinder. Both can emit percussive sound in the cylinder. Crankshaft bolts, nuts, connecting rod bolts, cross-head bolts in the crankcase are loose, tripped, broken, etc., the shaft diameter is severely worn, the gap increases, the cross-head pin and the bushing match the gap is too large or the wear is serious, etc. There was a crashing sound in the crankcase. The exhaust valve piece is broken, the valve spring is loose or damaged, the load regulator is adjusted improperly, etc., can make a knocking sound in the valve cavity. From this to find the fault and take measures.

   overheating fault

   At the friction between crankshaft and bearing, crosshead and sliding plate, packing and piston rod, 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, and the other is the accumulation of overheated heat that will burn the friction surface and burn and cause serious machine accidents. The main causes of bearing overheating are: uneven fit between the bearing and journal or too small contact area; bearing deflection and crankshaft bending or twisting; lubricating oil viscosity is too small, the oil circuit is blocked, the oil pump is faulty and the oil is cut off; during installation There is no leveling, no gap is found, the main shaft and the motor shaft are not aligned, the two shafts are tilted, etc.

   Compressor accident

   fracture accident

Crankshaft fracture: Most of the fractures are at the transition between the journal and the crank arm. The reasons are roughly as follows: the transition fillet is too small, r is the crankshaft journal); during the heat treatment, the fillet is not processed to make the junction Stress concentration occurs at places; rounded corners are processed irregularly, and there are partial cross-sectional mutations; long-term overload operation, and some users randomly increase the speed in order to increase the output, which makes the stress condition worse; the material itself has defects, such as sand holes and shrinkage in the castings. Song wait. In addition, it can also be seen that the oil hole on the crankshaft cracks and causes the fracture.

Breaking of connecting rod: There are several situations: connecting rod screw is broken, and the reasons are: plastic deformation of connecting rod screw after long-term use; poor contact between screw head or nut and the end face of the big end produces eccentric load, which can be as large as the bolt. As much as seven times the pure axial tension, therefore, no slight skew is allowed, the contact should be evenly distributed, and the distance between the contact points should not exceed 1/8 of the circumference, which is 450; the bolt material processing quality is problematic .

Piston rod fracture: The main fracture sites are the thread connecting the crosshead and the thread of the fastening piston. These two places are the weak links of the piston rod. If due to negligence in design, sloppy manufacturing and operational reasons , Break more often

   happened. If there is no problem in ensuring the design, processing, and material, the pre-tightening force during installation should not be too large, otherwise the piston rod will break when the maximum force reaches the yield limit. After long-term operation, due to the excessive wear of the cylinder, the piston in the horizontal row will sink, which will generate additional load at the connecting thread. If it continues to run, it may break the piston rod. This should be paid special attention to during maintenance. In addition, due to damage to other parts, the piston rod may break when the piston rod is subjected to a strong impact.

Cylinder and cylinder head rupture: The main reason: For water-cooled machines, if you forget to drain the cooling water in the cylinder and cylinder head after stopping in winter, the cooling water will freeze and break the cylinder and cylinder head, especially in In the northern part of our country, the cooling water must be drained after parking; the temperature of the cylinder rises because the water is interrupted in operation and it is not found in time, and the cooling water is suddenly put in, causing the cylinder to burst; because the dead center gap is too small, the piston Loose nut, as well as metal objects falling into the cylinder and plugging out of the piston will cause the piston to hit the cylinder head and cause it to break.

   Burning and explosion accidents

The problem of carbon deposits often occurs in oil-lubricated compressors, which is undesirable because carbon deposits will not only cause the piston ring to be stuck in the groove, the valve will not work properly, and the air flow channel area will decrease and increase the resistance. Under certain conditions, carbon deposits will burn, leading to an explosion accident in the compressor. Therefore, the lubricating oil in the cylinder cannot be supplied too much, and the gas that is not well filtered and contains a large amount of dust can not be sucked into the cylinder, otherwise the formation of carbon deposits and the gas containing a large amount of volatile matter may cause an explosion. In order to prevent combustion and explosion, it is necessary to plan maintenance and regularly clean the grease on the gas tank and pipeline.

   In addition to this, the compressor combustion and explosion accidents are caused by the following operational reasons: the compressor did not use low-pressure nitrogen to drive the air clean and cause an explosion before the compressor was tested with hydrogen, oxygen, nitrogen and hydrogen. Due to lack of operating knowledge, the valve from the compressor to the gas storage tank was not opened after driving, resulting in a sharp increase in exhaust pressure and an explosion. Therefore, to prevent such accidents, 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, the compressor operators should be trained before starting their jobs.

   Because the compressor high pressure stage gas valve is not tight, the high pressure and high temperature gas is returned to the cylinder, and high temperature is generated 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 leaking parts, and eliminate the fault at this time.