Knowledge sharing on oil bath screw compressors*

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1. Structural components of the oil bath type screw compressor (Ingersoll Rand): Head section: synchronous gears, male and female rotors, bearings, housing, mechanical seal, gear pump, etc. Lubricating oil system: oil-gas separator, temperature control valve, oil filter, check valve, cooler, solenoid valve. Control logic: one main unit and one backup unit, load/lead control mode. Cooling system: finned air-cooling type. Working principle: The compressor is composed of male and female rotors, synchronous gears, etc.; its operation proceeds in three stages: intake, compression, and exhaust. The screw air compressor achieves volume changes in the cylinder through the meshing of the screws, thereby completing its working process. (1) Inhale. At startup, the intake valve is closed and the unit operates at no load, maintaining the system pressure necessary for the lubricating oil to circulate. When a signal indicating loading or low system pressure is received, the intake valve opens; the unit begins to draw in air through the intake filter. The lubricating oil, after passing through the oil-gas separator, returns to the compressor head from below and mixes with the gas, entering the volume chambers of the male and female rotors. As the mating surfaces of these rotors gradually increase in size, the volume expands and the pressure decreases. A pressure difference is created at the intake port, drawing in more gas, until the volume of the rotors reaches its maximum value. At this point, the suction process ends; simultaneously, the tooth peaks of the rotors seal against the casing, forming a sealed working volume that is ready for the compression process. (2) Compression. As the rotor chamber rotates, its volume gradually decreases, causing the gas pressure to rise, thus completing the compression stage. (3) Exhaust. When it rotates to the exhaust port position, the volume of the gas inside reaches its minimum. Once the sealed space between the male and female rotors is connected to the exhaust port, the oil-gas mixture is discharged from the device into the separator. There, the oil and gas are filtered and separated in a storage tank; the efficiency of this separation depends on the setting of the minimum pressure valve as well as the residence time of the oil-gas mixture in that tank. Subsequently, the opening degree of the temperature control valve determines whether the mixture enters the cooling system, depending on the temperature. This process of drawing in air, compressing it, and discharging it repeats periodically, thereby enabling the compression and transportation of air. Summary of system components: motor, head, intake valve, release valve, exhaust valve, outlet check valve, intake filter, oil-gas separator, minimum pressure valve, oil filter, temperature control valve, cooler, drying unit, pressure and temperature gauges, sensors. Startup procedures and things to note during shutdown: During startup, it is necessary to check whether the process flow is intact, whether there are any alerts on the control panel, whether there are any leaks at the pipeline connections, the liquid level in the oil tank, the belt of the cooling fan, the drainage of condensate from the cooler, the set value of system pressure, and the pressure difference between the inlet and outlet of the oil filter. During shutdown, the standby unit should be smoothly brought online while the main unit is being shut down. Then, the compressor outlet valve should be opened gradually, in order to avoid large fluctuations in system pressure. After that, the operation mode should be changed to automatic, with the main unit stepping back to standby mode. During normal shutdown, the outlet valve of the compressor system should be closed to prevent backflow of pressure in the piping network and to release the pressure at the compressor outlet. Common fault issues: high outlet temperature, low outlet pressure, poor oil-gas separation, inability to load or unload, excessive vibration, high load, abnormal noises, lubricant leakage, and poor cooling performance.