Frequently Asked Questions about Screw Air Compressors

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Frequently Asked Questions about Screw Air Compressors 1. High exhaust temperature of the unit (above the set value of 110 ℃), causing the air compressor to shut down automatically. 1) Insufficient lubricating oil in the unit (the oil level is below the green mark indicated on the oil sight glass when the unit is stopped)； 2) The ambient temperature exceeds the specified range (38°C). 3) The cooling fins of the oil cooler are clogged with dust; it is necessary to blow from the inside out ； 4) Incorrect lubricant specification ； 5) Thermal control valve failure ； 6) The imported air filter is dirty ； 7) Clogged oil filter element ； 8) Cooling fan failure ； 9) The exhaust duct is not unobstructed or the exhaust resistance (back pressure) is high ； 10) Temperature sensor failure (control unit) ； 2. The exhaust temperature of the air compressor is below normal (below 75°C). 1) Excessive amount of cooling water. 2) Low ambient temperature. 3) Operating without load for too long. 4) Error in the reading of the temperature sensor. 5) Faulty thermal control valve, remaining in the open position. 3. High fuel consumption of the unit, short interval between lubricant top-ups, or high oil content in the compressed air output ； 1) There is too much lubricating oil; when the machine is stopped, the oil level is above the green mark on the scale. During operation, the oil level should not exceed half of the scale mark ； 2) Clogged return oil pipe ； 3) The exhaust pressure is too low during unit operation ； 4) Malfunction of the intake valve check valve function ； 5) The oil fine separation filter element is damaged ； 6) Cooling oil system leakage ； 7) Spring fatigue in the outlet pressure maintenance valve for oil and gas tanks 8) Failure of the check valve in the return oil pipe 9) Incorrect specification of the lubricating oil 4. The compression volume of the unit is below the designed value, with low outlet pressure 1) Clogging of the inlet air filter 2) Improper operation of the inlet valve, or damage to the diaphragm inside the loading valve or the solenoid valve ； 3) The outlet pressure maintenance valve is not functioning properly ； 4) Clogging of the oil fine separation filter element ； 5) Pressure relief valve leakage ； 6) The intake proportion valve is set incorrectly. 7) The belt connecting it is loose ； 8) The actual gas consumption is greater than the gas output of the unit ； 9) Pressure sensor failure (control unit) ； 5. Excessive exhaust pressure of the unit 1) Faulty intake valve ； 2) Fault in the inlet loading solenoid valve ； 3) The pressure setting is too high ； 4) Pressure sensor failure (control unit) ； 5) Pressure gauge failure (relay-controlled unit) ； 6) Pressure switch failure (relay-controlled unit). 6. The unit cannot start (electrical fault) 1) Fuse blown ； 2) Main motor protection relay trips ； 3) Starter relay failure ； 4) Under-phase protection relay operates ； 5) Poor contact of the start button, loose wiring ； 6) Voltage is too low ； 7) Motor failure ； 8) Mechanical failure ； 9) Control unit without power input ； 10) Controller failure, pressure and temperature sensors disconnected ； 7. High current during unit startup causes the compressor to trip automatically (electrical fault). 1) The input voltage is too low ； 2) The exhaust pressure is too high, exceeding the rated pressure ； 3) Incorrect lubricant specification ； 4) Clogging of the oil fine separation filter element ； 5) Host failure ； 6) Main motor failure ； 7) Stars – The interval between triangle conversions is too short (it should be 10 ~ 12 seconds) ； 8) Intake valve failure (excessive opening degree or stuck in the open position) ； 9) Loose wiring ； 10) The TR time relay is damaged (the relay controls the unit). 8. The operating current of the main unit is below the normal value. 1) High air consumption (the outlet pressure remains below the set value during operation). 2) The inlet air filter is clogged, causing the main unit to operate at a low load ； 3) Poor operation of the intake valve, damage to the diaphragm inside the servo cylinder, or a faulty solenoid valve, resulting in the intake valve not opening fully ； 9. The main unit cannot operate at full load 1) Faulty three-way solenoid valve 2) Faulty intelligent controller 3) Improper operation of the intake valve 4) Ruptured diaphragm in the servo cylinder of the intake valve 5) Improper operation of the pressure maintenance valve 6) Faulty proportional valve 7) Air leakage from the water filter 8) Leakage in the control pipelines 10. Frequent switching between light and heavy load conditions 1) Pipeline leakage 2) Too low differential pressure setting 3) Unstable air consumption 11. Oil mist escaping from the inlet air filter when the machine is shut down 1) Intake valve leakage 2) Shutdown under heavy load 3) Improper operation of the three-way solenoid valve 4) Incorrect electrical wiring 5) Leakage in the pressure maintenance valve 6) Relief valve not releasing pressure 12. Overload of the fan motor 1) Deformed fan ； 2) Fan motor failure ； 3) Fan motor thermal relay failure (aging) ； 4) Loose wiring ； 5) Cooler blockage ； 6) High exhaust resistance. 13. Working principle of screw compressors: Screw air compressors are a type of positive-displacement compressor; they achieve gas compression by gradually reducing the working volume. The working volume of a screw air compressor is composed of the toothed grooves of a pair of rotors that are placed parallel to each other and mesh with one another, along with the casing that encloses these rotors. When the machine is in operation, the teeth of the two rotors interlock with each other’s tooth grooves. As the rotors rotate, the teeth that are inserted into the opposing tooth grooves move toward the exhaust side, causing the volume enclosed by those opposing teeth to gradually decrease and the pressure to rise. Once the desired pressure is reached, that tooth groove becomes connected to the exhaust port, thereby enabling exhaust. When a tooth groove is inserted by the corresponding tooth on the opposite side, two spaces separated by the teeth are formed; the tooth groove near the intake end serves as the intake volume, while the one closer to the exhaust end functions as the volume for compressing the gas. As the compressor operates, the teeth of the opposite rotor that are inserted into the tooth grooves move toward the exhaust side, causing the suction volume to continue expanding while the volume of the compressed gas continues to shrink. This enables a suction and compression process in each tooth groove. When the gas pressure in a tooth groove reaches the desired exhaust pressure, that groove becomes aligned with the exhaust port, and the exhaust process begins. The changes in the suction volume and compression volume, which are divided by the teeth of the opposite rotor’s teeth, occur repeatedly, thereby enabling the compressor to continuously suck in air, compress it, and discharge it. 14. Pre-startup precautions: 1) Check the three-phase power supply to ensure it is functioning properly. 2) Open the machine door lock and check the oil level of the air compressor; it should be within the green range on the oil level scale. If not, Skelco screw compressor-specific oil must be added until the level is normal. 3) Turn on the power lock of the controller and check whether there are any abnormal displays on the LCD screen. It should normally display “Device is shut down”, indicating normal operation. 4) Open the air compressor outlet valve. 5) Once the above checks are complete and correct, press the compressor start button, namely the (ON) button, and the compressor will begin to operate properly. 15. Precautions during operation: 1) After starting up, observe the air compressor running for 3–5 minutes. Check for any abnormal noises or vibrations, as well as any leaks of oil or gas; otherwise, the machine should be stopped immediately for inspection. 2) There is pressure in the pipelines and containers that are in operation; it is strictly prohibited to loosen the pipelines or plugs, as well as to open unnecessary valves. 3) Pay attention to monitoring the oil level during operation. It is normal for the oil level to drop slightly while the machine is running compared to when it is shut down. If the oil level cannot be seen and the exhaust temperature is high, the machine should be stopped immediately. After shutting down the machine for 10 minutes, check the oil level; if it is insufficient, add the appropriate lubricant when there is no pressure inside the system ； 4) After the gas is cooled by the oil cooler, some condensate water is generated, which should be drained regularly; otherwise, this water will be carried by the gas into the subsequent systems ； It can be adjusted flexibly depending on weather conditions and the timing of water discharge, with more frequent occurrences generally in summer. 5) During operation, parameters such as voltage, current, outlet gas pressure, outlet exhaust temperature, and oil level should be recorded at least every 1–2 hours, for use as a reference during future maintenance. 16. Precautions for shutting down: 1) First, press the OFF button; after 10–15 seconds, the intelligent controller will shut down according to the pre-programmed sequence. Only then will the motor stop. Avoid shutting down the air compressor directly under heavy load ； 2) If necessary, turn off the power lock switch (red button) to disable the power lock. 3) After the air compressor stops, it cannot be started immediately; wait for about 1–2 minutes until the internal pressure of the system is automatically released, to prevent damage to the motor due to starting under heavy load. 4) After debugging, adjust the pressure and other parameters according to actual conditions, and set it to full automatic control mode. Under normal circumstances, users do not need to make any adjustments on their own. 17. Maintenance of the intake air filter: Dust in the incoming air is trapped within the filter to prevent premature wear of the compressor and clogging of the oil separator. The air filter should generally be replaced after 1,000 operating hours or after one year; in areas with a high level of dust, the replacement interval should be shortened. The machine must be shut down during filter maintenance; to reduce the downtime, it is recommended to install a new or cleaned spare filter. The steps to clean the filter are as follows: a. Gently tap both ends of the filter alternately against a flat surface to remove most of the heavy, dry dust. b Blow dry air at a pressure of less than 0.2 MPa in the opposite direction to the incoming air (from inside to outside); the nozzle should be at least 25 millimeters away from the folded paper, and blow upward and downward along its length. c If there is grease on the filter element, it should be replaced with a new one. A light source is placed inside the filter for inspection; if thinning, pinholes, or damage are detected, it should be discarded. 18. Cleaning of the outlet oil cooler (air-cooled units): Special attention must be paid to keeping the outer surface of the plate-fin cooler clean, as otherwise the cooling efficiency will be reduced; therefore, it should be cleaned regularly depending on operating conditions. Cleaning method: During major repairs, use a fiber brush to remove dust from the cooler; never use brushes made of wire or any metal objects for dust removal ； Then, compressed air is used to purge the cooler in the opposite direction to the cooling air (from inside to outside). 19. Internal process of the refrigerated dryer: The refrigerant used in the refrigerated dryer is R22. This refrigerant is compressed into a high-temperature, high-pressure gas, and then cooled in a water-cooled condenser to become a low-temperature, high-pressure liquid. It subsequently passes through a thermal expansion valve, where it exchanges heat with the compressed air, thereby reducing the temperature of the compressed air. 20. Location and function of the instrument air and plant air connection valve: When the instrument air or plant air compressor fails to operate, opening this connection valve ensures that both types of air are available, thereby meeting the needs of subsequent processing stages for a short period of time. 21. Increased noise: a. Damage to the bearing at the intake side – remove and replace it. b. Damage to the bearing at the exhaust side – remove and replace it. c. Damage to the motor bearing – remove and replace it. 22. What is the purity standard for nitrogen? What is a nitrogen analyzer used to measure? The purity of nitrogen Purity ≥ 99.8﹪; the nitrogen analyzer indirectly determines the purity of nitrogen by measuring the oxygen content in the gas. 23. If the refrigerant pressure is not within the specified range, which valve should be adjusted? The high pressure (condensation pressure) is not within the specified range; adjust the return valve for the circulating water in the condenser ； The low pressure (evaporation pressure) is not within the specified range; adjust the hot gas bypass valve. 24. If a cold dryer shuts down, can it be restarted simply by turning it on again? If the shutdown is triggered due to high refrigerant pressure, it is necessary to open the bottom cover; otherwise, press the reset button to reset it ； If the unit shuts down due to motor overload, it is necessary to reset it using the reset button located in the electrical control cabinet before the refrigeration dryer can be restarted. 25. Why is the dew point temperature of the cold dryer controlled at 2-8°C? Excessively high dew points increase the moisture content in the gas; upon entering the adsorption tower, this leads to the pulverization of the adsorbent, thereby reducing its service life ； The dew point is too low. 26. Why is a cold dryer paired with an air compressor? Since the capacity of the cold dryer is 15 m3/min, each nitrogen generation air compressor has a gas production rate of 15.9 m3/min. 27. How long after the refrigerated dryer starts does it take for the conditions to be met so that the nitrogen generation compressor can be started? After the cold dryer has been running for 15 minutes, the compressor can be started once the pressure gauge reads within the green range. 28. What gauges should be checked during nitrogen production inspection operations? 1) Circulating water pressure and temperature 2) Gas pressure and temperature at the compressor outlet 3) Condensing pressure and evaporation pressure of the refrigerated dryer 4) Whether the indicators of the pre-filter and the primary and secondary fine filters are in the green zone 5) Nitrogen pressure, flow rate, and purity. 29. What conditions must be met after the compressor starts up before air can be sent to the adsorption tower? After the compressor starts, air can be supplied to the adsorption tower only when the pressure reaches 0.7 MPa. 30. How often should the filter of the cold dryer be drained, and what is the duration of each drainage? Drain water every 2 minutes, with a drainage time of 4 seconds. 31. Why is the opening degree of the flow control valve at the nitrogen production station used to control the flow rate of nitrogen being delivered, thereby regulating the purity of the nitrogen? Since the flow rate determines the adsorption time of the gas within the adsorption tower, that is, the adsorption time of oxygen molecules. When the flow rate is high while the pipe diameter remains unchanged, the flow velocity increases, the oxygen adsorption time shortens, and the residual oxygen content in the product rises; as a result, the purity of nitrogen decreases. Conversely, the purity increases. 32. What is the capacity of the main instrument air tank? Why is such a large storage tank needed? The volume is 2×69 = 138 m3. The purpose is to ensure that the remaining pressure and air in the large storage tank can still support the normal operation of the instruments in subsequent processes for a certain period of time after the air compressor fails and shuts down, and to provide enough time to start the backup unit promptly, thereby minimizing the impact on production. 33. Why are filters and dryers installed for instrument air in the air compressor station? Since instrument air is used for precision instruments, the presence of oil and moisture can cause the instruments to become clogged and stop functioning, thereby reducing their service life. 34. What are the requirements regarding the oil content of the gas entering the adsorption dryer? The oil content of the gas entering the adsorption dryer must be controlled to be less than 3 mg/m3. 35. What is the principle of nitrogen adsorption? Taking full advantage of the difference in size between oxygen molecules and nitrogen molecules, specially treated activated carbon (carbon molecular sieve) is used; the pore sizes of its carbon molecules fall within the diameter range of nitrogen and oxygen molecules. Since oxygen molecules are smaller in size and lighter in weight than nitrogen molecules, they are adsorbed on the surface of the carbon molecular sieve first, after which the material is regenerated by reducing pressure. 36. What are the reasons for the automatic shutdown of the PSA system? 1) Low pressure in the air buffer tank. 2) Failure of the cold dryer. 3) Excessively high oxygen content. 37. What is desorption? When the carbon molecular sieve becomes saturated with oxygen molecules and can no longer absorb any more, most of these molecules are released under reduced pressure; this process is known as desorption. 38. How many components does a nitrogen system consist of? 1) Compressed air generation and pre-treatment 2) Air separation 3) Nitrogen storage 4) Gas supply 39. How is a nitrogen production system started up? 1) First, start the cold dryer to get it operating. 2) Check whether the operating current of the cold dryer is within the normal range. 3) After the cold dryer has been running for about 15 minutes and the pressure gauge indicates a value within the green range, start the compressor until it operates properly. 4) Turn on the air compressor to supply compressed air to the inlet valve of the cold dryer, thereby allowing compressed air to enter the cold dryer. 5) Check whether the cold dryer is functioning properly. 6) Check whether the temperatures at the inlet and outlet of the cold dryer are within the normal range. 7) Check whether the high and low pressures of the refrigerant are within the normal range. 8) After 10 minutes of operation, check whether the drainage system of the cold dryer is working properly. 9) Once the compressor is operating properly, start the PSA system and open the main valves at both the front and back of the PSA system. 10) Monitor the temperatures and pressures of the adsorption tower and regeneration tower from the control panel; record the time when switching between the operation of these two towers, and check whether the valves are opening and closing properly. 11) Once nitrogen of qualified quality is produced, and the buffer pressure of the nitrogen reaches 0.5 MPa (higher than the pressure in the nitrogen storage tank), open the flow control valve of the nitrogen production station and gradually increase the nitrogen pressure ； 12) When the pressure in the nitrogen storage tank reaches 0.7 MPa, the main discharge valve is opened in accordance with the dispatch requirements. 40. How does an air compressor achieve automatic unloading? The adjustment of the air compressor’s output volume is achieved by installing an intake valve on the inlet duct. When the pressure of the gas discharged from the cylinders exceeds the specified value, the pressure regulator comes into action; it operates the servo cylinder to move the intake valve, thereby closing off the air flow and allowing the air compressor to operate without a load, thus saving electricity consumption. 41. What items should be checked before operating a cold dryer? 1) Check if the voltage is abnormal. 2) What is the ambient temperature? 3) Check the condition of the condenser and cooling water. 4) Determine whether compressed air can reach the refrigeration dryer. 5) Check if the condensing pressure indicated on the refrigerant gauge is normal. 6) Check if the cooling water and its temperature are normal