1 working principle of air compressor The SA-250W compressor is produced by Fusheng Company. It is a gardnerDenver (Dengfu) main engine. The typical water-cooled fuel injection twin-screw air compressor has a displacement of 42m 3 / min, a rated discharge pressure of 0.75MPa and a motor power of 250kW. The speed is 1480r/min. The compressor is mainly composed of several systems such as main engine, cooling and lubrication, oil and gas separation, gas volume adjustment and electrical control. The SA-250W fuel injection twin screw air compressor is a two-shaft positive displacement rotary compressor. The compressor main unit is composed of a pair of female and male rotors and a casing. The main rotor has four helical teeth that are 90-distributed with each Other, and the female rotor has five spiral grooves that are 60-shaped. The two teeth are in mesh with each other . The main rotor directly drives the secondary rotor to rotate together. When the rotor is not engaged at the suction port, air flows into the cavity of the main rotor convex tooth and the secondary rotor groove, and the compression cycle starts. When the rotor is disengaged from the suction port, the air is enclosed in the cavity formed by the main and auxiliary rotors, and moves axially with the meshed rotor. When the meshing continues, more main rotor teeth enter the groove of the auxiliary rotor. The volume is reduced and the pressure is increased. Until the inter-tooth volume port is in communication with the exhaust port. During the compression process, the nozzles on the wall of the housing continuously inject cooling oil into the compression chamber, and the cooling oil takes away 80% of the heat generated during the compression process, and at the same time acts as a lubrication and sealing. The cooling oil and the compressed air are discharged together outside the machine, and are separated by oil and gas, cooled, filtered, and recycled. 2 common fault analysis and its treatment The reliability of the SA-250W compressor main engine is very good, and there are few problems in the case of good daily maintenance. The main faults occur in cooling lubrication, oil separation, and gas volume regulation systems. 2.1 host exhaust temperature over temperature The normal exhaust temperature of the SA-250W compressor should be between 77 and 94 °C. When the temperature is lower than the pressure dew point, condensation will occur, which will cause more moisture in the system, and the lubricant will be emulsified, which will affect the lubrication effect. Excessively high exhaust temperatures can cause damage to many components and severely burn the mainframe. The SA-250W screw air compressors are designed with ultra-high temperature protection. Once the temperature sensor detects that the head exhaust temperature exceeds 100 °C, the red light is on and the compressor stops running. When the exhaust temperature of the machine exceeds 95 °C, the red light flashes, and the LCD screen indicates that the exhaust temperature is too high, that is, troubleshooting should be performed. 2.1.1 Checking the thermal control valve The thermal control valve is a three-way valve. The first function is that when the air compressor is started, the bypass of the thermal control spool is opened, so that the oil is directly sprayed from the oil and gas barrel into the main engine to accelerate the rise of the oil temperature and prevent the water vapor in the compressed air from condensing in the oil separator. Second, after the air compressor is in normal operation, the oil temperature is adjusted according to the proportion of the oil cooler and the bypass, and the oil temperature is controlled to keep the injection temperature of the air compressor at the optimum point. If the temperature control valve fails, the hot oil may not be directly sprayed into the main unit without the oil cooler cooling, causing the air compressor to overheat. In the form of failure of the temperature control valve, first, the temperature sensing element is aging, the expansion and contraction curves are distorted, and the normal operation cannot be performed with temperature changes. Second, the valve body is worn and the valve action is not in place. The thermal control valve should be fully opened at 66 °C. If it is not open, all parts of the thermal control valve should be thoroughly cleaned, otherwise the thermal control valve should be replaced. 2.1.2 Checking the cooler The dirt on the inner and outer surfaces of the cooler will affect the heat dissipation and reduce the cooling effect, so the cooler should be cleaned regularly. The dirt on the outer surface of the cooler is mainly the sludge formed by cooling oil and dust. It is sprayed with low pressure steam and has a good effect. The fouling in the cooler tube is mainly the coke produced during the oil circulation. It can be found by checking the inlet pressure and outlet pressure of the water. The pressure drop of the water should be between (0.3~0.7)×105 Pa, any abnormal value. The pressure drop indicates that the pipeline is clogged, it needs to be flushed with special cleaning fluid, or the carbon can be removed by special cleaning steel brush, and the carbon can be removed. 2.1.3 Checking the oil filter SA-250W oil filter is a paper filter. Its function is to remove the impurity metal particles in the oil. The filtration precision is below 10μm. It has perfect protection for the bearing and the rotor. The filter element is easy to block, resulting in insufficient power supply to the main engine. The exhaust is over temperature. The SA-250W air compressor control panel is equipped with an oil filter front and rear differential pressure alarm indicator. When the light is on, the filter element should be replaced in time. 2.1.4 Checking the oil level The oil level of the oil and gas barrel is too low, which also causes the exhaust temperature to be over temperature. When the unit is running, the oil level gauge pointer must be in the yellow area, and the space time machine must be refueled in the red area. 2.2 host exhaust oil exceeds the standard 2.2.1 Check the oil level of the fuel tank In order to ensure the effect of oil droplet collision and centrifugal separation, the flow rate of the oil-air mixture after entering the lower part of the separator is high. If the oil level of the oil tank is too high, the high-speed airflow will entrain the oil in the oil tank into the compressed air, resulting in the air compressor row. Gas and oil exceeded the standard. Therefore, oil and gas barrel oil level should be strictly controlled within the Yellow Zone. 2.2.2 Checking the pressure maintenance valve The role of the pressure maintenance valve is mainly reflected in the first, the minimum pressure required to ensure the oil circulation of the unit. The second is to prevent the high pressure gas in the pipe network from being poured back into the oil separator. The third is to ensure that the pressure difference between the oil separator and the separator is not too large, reduce the gas velocity, and ensure the fine separation of the oil. The SA-250W air compressor pressure maintenance valve is installed at the outlet of the oil separator above the oil and gas tank, and its opening pressure is set at about 0.45 MPa. The opening pressure is too low, the pressure difference between the oil separator is large, the gas flow rate is high, and the oil condensed on the cylinder wall is swept away by the high-speed airflow, which affects the effect of coarse separation and also affects the oil mist on the oil separation core. Adsorption. 2.2.3 Checking the oil separator The filter element of the oil fine separator is composed of a plurality of fine glass fibers, and the misty oil contained in the compressed air can be almost completely filtered by the oil separator, and is less than 3×10-6. The service life of the filter element of the oil fine separator is related to the degree of contamination of the cooling oil and the amount of oil flowing through the oil separation core. After long-term use, impurities such as dust, metal abrasives, and colloidal impurities in the cooling oil block the pores of the fiber. When the gas is passed, the pressure drop is increased, and even the separator core is broken down, completely losing the separation ability. A fine separator pressure difference switch is installed between the oil and gas barrel and the oil separator. When the pressure drop of the fine oil separation core is >0.055MPa, the differential pressure indicator light flashes, indicating that the oil separator is blocked, and should be immediately replace. When the pressure drop of the fine oil separation core is >0.1MPa, the differential pressure indicator light is always on and the unit is stopped. 2.2.4 Checking the return line The return line of the SA-250W air compressor consists of the oil pipe and the orifice joint. Blocking the oil return orifice will cause the oil level in the oil separator core to be high and increase the oil content of the exhaust gas. When installing the return pipe, the distance from the bottom of the oil separator core should be strictly controlled. If the distance is too large, the oil level at the bottom of the oil separator core is too high, and the accumulated oil will be re-entered into the compressed air by the airflow, causing the exhaust oil to exceed the standard. If the distance is too small, the oil pipe inlet is blocked, which also causes the oil level to be too high. A suitable value for this installation distance is between 2 and 4 mm. In order to prevent the oil return orifice from being blocked, some maintenance personnel often remove the orifice joint, which is not appropriate. Because the function of the orifice is to reduce the flow area of ​​the return pipe. The oil return pipe is connected to the air inlet of the compressor main body, and the passage diameter affects the displacement of the compressor (the compressed gas in the oil fine separator expands after entering the suction chamber to reduce the intake air amount of the compressor), and increases The power consumption of the compressor reduces efficiency. 2.3 host exhaust pressure is low The source of low air compressor discharge pressure is mainly concentrated on the intake and exhaust passages. The throttling factor should be focused on the intake passage. The exhaust passage should mainly consider the leakage point inside the machine and the resistance source that causes large pressure loss. 2.3.1 Checking the air filter On the intake line, first check the air filter. The air filter core is clogged with dust, which will cause the air compressor to have insufficient air intake and low exhaust pressure. The SA-250W air filter is a dry filter, and the paper filter has a short life and high consumption in harsh environments. The dust on the surface should be removed every 1000h. The way to remove it is to use low-pressure air to blow the dust from the inside out. The air filter is equipped with a differential pressure detector. If the air filter indicator on the instrument panel is on, the air filter must be cleaned or replaced. 2.3.2 Inlet valve opening is not enough The intake valve is not fully opened, and the air compressor intake is insufficient, which may cause the exhaust pressure to be low. The intake valve of the SA-250W air compressor adopts piston type control. When loading, the piston is controlled by the loading solenoid valves IVC and IVO to push the intake valve to open. Factors that cause insufficient intake valve opening are: piston wear and seizure. The two-position three-way solenoid valve coil is burned or the spool is damaged, causing the piston to not work. 3 Conclusion The air compressor's cooling and lubrication system, oil and gas separation system, and gas volume adjustment system are the key systems to ensure the normal operation of the machine. According to our statistics in recent years, the failure of these systems accounts for more than 80% of the total machine failure. These faults occur mostly with two (oil cooler and air aftercooler), three cores (air filter core, oil separator core, oil filter core), four valves (Check valve, pressure maintenance valve, oil cut) Solenoid valve, thermal control valve) related. To ensure the normal operation of the machine, you must do the routine maintenance of these components, clean the two devices regularly, and replace the three filters as required. swing check valve,High Quality swing check valve,swing check valve Details, Tianjin Tanggu Jinbin Valve Co., Ltd. Water control valve Co., Ltd. , http://www.stainless-steel-valva.com