System flow of screw air compressors and functions of various components

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System flow of screw air compressors and functions of various components 1. Air flow 1.1 After dust is removed by the air filter, air enters the main compression chamber through the intake valve where it is compressed and mixed with lubricating oil. The compressed air mixed with oil is discharged into the oil-gas tank, and then, after passing through an oil fine separator, a pressure maintenance valve, and a rear cooler, it is sent to the system for use. 1.2 Function descriptions of various components in the main air supply circuit: A. Air filter – The air filter is a dry paper filter, with the pore size of the filtering paper being around 5μm. Its main function is to remove dust from the air, preventing premature wear of the screw rotor as well as premature clogging of the oil filter and oil fine separator. Generally, after 500 hours of operation, it should be removed to clean the dust from its surface. The method of removal is to use low-pressure air to blow the dust out from the inside. B intake valve: The intake valve is a disc-type valve, and it controls the light and heavy loads by opening and closing the disc inside the valve ； There are two control methods: one is on/off type, where the air inlet is closed when the pressure reaches the upper set value, and it is reopened for full-load operation once the pressure drops to the lower set value. Another type of capacity control involves the slight closure of the disc in the intake valve, in combination with a proportional valve, to regulate capacity and adapt it to the external demand for air, thereby keeping the pressure within a certain range. When the pressure does not reach the set value for capacity control, the disc in the intake valve opens fully, allowing the compressor to operate at full load. C Oil and gas tank: The oil and gas tank serves two functions – separating oil from gas and storing oil. The compressed oil-gas mixture is discharged into an oil-gas tank, where rotation within this tank allows most of the lubricating oil to be separated out ； The oil tank contains a large amount of lubricating oil, which prevents the freshly separated hot oil from immediately participating in the next cycle, thereby helping to reduce the exhaust temperature. A oil level gauge is installed on the side of the oil and gas tank. The barrel has a filling hole for adding oil; the level of the static lubricating oil should be between the upper and lower limits indicated by the gauge. A drain (water) ball valve is installed below the oil and gas tank; it should be slightly opened before each operation to remove the condensed water inside the tank (as water is denser than oil and settles at the bottom). Once oil starts leaking, shut it off immediately. Due to the large cross-sectional area of the oil and gas tank, the flow velocity of compressed air can be reduced, which facilitates the separation of oil droplets and serves as a preliminary oil removal step. The D-oil fine separator is described in detail in the \"lubricating oil flow\", which is omitted here. The E safety valve activates automatically to release pressure when the gas pressure inside the oil and gas tank exceeds 1.1 times the rated discharge pressure, thereby reducing the pressure below that rated value. To check the safety valve, operate the compressor at full load and gently pull the release lever on the safety valve; if it can discharge air outward, it is considered to be in good condition. The minimum pressure valve F is located at the outlet of the fine oil separator, above the oil-gas separator. Its opening pressure is set at around 0.45 MPa. The main functions of this minimum pressure valve are as follows: a. It ensures that the circulation pressure required for lubrication is established first during startup, thereby guaranteeing proper lubrication of the machine. b. The oil and gas tank should be opened only when the gas pressure exceeds 0.4 MPa; this helps to reduce the air flow rate passing through the fine oil separator. It not only ensures effective oil separation but also protects the separator from damage caused by excessive pressure differences. c. Check valve function: It prevents compressed air from flowing back in the pipeline when the pressure in the oil and gas tank drops after shutdown. The compressed air flowing out of the minimum pressure valve is sent to the after-cooler. The aftercooler and the oil cooler are integrated into one unit; they have the same structure, both being of the plate-and-flange type. The cooling fan draws in cold air and blows it over the cooler latches. The temperature of the cooled compressed air is generally below the ambient temperature plus 15°C. 2. Lubricating oil circuit 2.1 Description of the lubricating oil circuit: The pressure inside the oil and gas tank forces the lubricating oil out of it; it then passes through an oil cooler and an oil filter to have any impurity particles removed. After that, the oil is divided into two streams – one of which is injected into the compression chamber at the bottom of the engine to cool the compressed gas ； The other path leads to both ends of the machine, where it lubricates the bearing assemblies; thereafter, the lubricating oil from these areas gathers at the bottom of the compression chamber and is discharged through the exhaust port. After the compressed air mixed with oil is discharged into the oil-gas tank, most of the oil settles at the bottom of the tank; the remaining air containing oil mist then passes through an oil fine separator, which further removes any remaining oil, allowing it to be used in the next cycle. 2.2 Control of oil injection volume: The oil injected into the air compressor serves not only as a lubricant but also primarily to remove the heat generated during air compression. The oil injection volume has been set by our company’s technicians prior to delivery; therefore, please do not change it arbitrarily. 2.3 Function descriptions of the main components in the oil circuit A. Temperature control valve: The main function of the temperature control valve is to regulate the exhaust temperature of the compressor by controlling the humidity of the lubricating oil injected into the compressor head, thereby preventing water vapor in the air from condensing inside the oil-gas tank and emulsifying the lubricating oil. At startup, the temperature of the lubricating oil is low, so the temperature control valve closes, and the cold oil is injected directly into the machine without passing through the cooler. If the oil temperature rises above 70°C, the temperature control valve gradually opens to allow flow to the oil cooler; it opens fully at 76°C, at which point the oil passes through the oil cooler for cooling before being injected back into the engine. Some models do not have a temperature control valve; instead, the oil temperature is controlled by stopping the fan motor. When the exhaust temperature rises to 85°C, the fan starts to operate ； When the exhaust temperature is below 75°C, the fan stops automatically to keep the temperature within a certain range. B. Oil cooler: The oil cooler is integrated with the aftercooler. C. Oil filter: The oil filter is a paper filter with a filtration precision of between 10μ and 15μ. Its function is to remove impurities from oil. Such as metal particles, dust, and degradation products of oil, to protect the proper operation of bearings and rotors. If the oil filter becomes clogged, it may result in insufficient fuel injection, which affects the service life of the engine’s bearings; at the same time, the exhaust temperature of the engine head increases (and in severe cases, the engine stops working). D. Fine Oil Separator: The filter elements of the fine oil separator are made from multiple layers of fine, special fibers. The mist-like lubricating oil contained in compressed air can be almost completely removed after passing through this separator; the size of oil particles can be kept below 0.1 μm, while the oil content can be reduced to less than 3 PPM. E. Return oil check valve: The residual oil filtered out by the oil fine separator collects in a small circular groove at the center of the filter element, and is carried back to the main engine via the return oil pipe, thereby preventing the lubricating oil that has been separated from being discharged along with the air. To prevent the oil in the compressor chamber of the host from flowing back, a check valve is installed after the oil return pipe. If the fuel consumption increases suddenly during machine operation, it is necessary to check whether the throttle orifice of the check valve is blocked. 3. Pneumatic control components A. Loading solenoid valve: It is a two-position, two-way normally closed solenoid valve. By activating and deactivating the solenoid valve, the on/off state of the air circuit is controlled, thereby enabling loading and unloading functions. The vent solenoid valve is a two-position, normally open solenoid valve. The on and off state of the air circuit is controlled by energizing and de-energizing the solenoid valve, thereby achieving the unloading function. B. Bleed valve: This valve opens during unload operation or when the machine is shut down, releasing pressure from the oil and gas tank so that the compressor can operate at a reduced load, or to enable restart without any load. C. The inverse proportion valve comes into effect only when the set regulation pressure is exceeded; at this point, the higher the proportion valve value (i.e., the system’s exhaust pressure), the lower the output control pressure. The lower the control pressure, the smaller the opening of the intake unloading valve disc controlled by the expansion and contraction of the cylinder, and thus the less air enters the compressor. This helps to maintain a balance between the air supply and air consumption of the compressor, enabling stepless regulation of the air volume. To adjust the pressure, lift the black cap of the inverse proportion valve and rotate it; rotating it clockwise increases the pressure, while rotating it counterclockwise decreases it. After setting it, press down the cap to prevent it from rotating on its own due to vibrations. The set value should generally be lower than the rated exhaust pressure; if it is higher than the unloading pressure set by the microcomputer controller, there is no room for adjustment other than with an empty vehicle. D. Sensors: Pressure and temperature sensors are used to measure various parameters, enabling the compressor to increase or decrease its load, providing alerts for various faults, and shutting down automatically when necessary. \ Last edited by The wise are not confused on 2009-3-17 08:41]