Analysis of compressor failure causes and countermeasures (1)

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.
     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 situation of damage. 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 exhaust volume:
     The insufficient exhaust capacity is compared with the design air capacity of the compressor. It can be mainly considered from the following aspects:
     1. Failure of the air intake filter: fouling and blockage reduce the exhaust volume; the suction pipe is too long and the diameter is too small, causing the suction resistance to increase and affecting the air volume. The filter must be cleaned regularly.
     2. The reduction in compressor speed reduces the displacement: the air compressor is used improperly, because the displacement of the air compressor is designed according to a certain altitude, suction temperature, and humidity. When it is used at a plateau that exceeds the above standards, When it is on, the suction pressure will decrease, etc., and the exhaust volume will inevitably decrease.
     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. 0.06/100~0.09/100; for aluminum alloy piston, the clearance is 0.12/100~0.18/100 of the air diameter; the steel piston can take the smaller value of the aluminum alloy piston.
     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 failure 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 warping, 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 compressing force of the compressed 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 a value greater than 1, generally 1.5~2.5, K=1.5~2.0 at low pressure, K=1.5~2.5 at high pressure. Taking K this way has been proven to be good in practice. If the air valve is faulty, the valve cover will inevitably become hot and the pressure will be abnormal.
     Exhaust temperature is abnormal
     Abnormal exhaust temperature means it is higher than the design value. Theoretically, the factors that affect the increase in exhaust temperature are: intake air temperature, pressure ratio, and compression index (for air compression index K = 1.4). 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.
     Abnormal pressure and reduced exhaust pressure
     If the air volume discharged by the compressor cannot meet the user’s flow requirements at the rated pressure, the exhaust pressure must be reduced. The reduction in the required exhaust pressure is a phenomenon. Its essence is that the exhaust volume cannot meet the user’s requirements. 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 noise
     If some parts of the compressor fail, it will make abnormal noises. Generally speaking, the operator can identify the abnormal noises. 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 is increased, 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.