Refrigeration compressor configuration application and precautions

Compressor configuration Generally speaking, semi-hermetic compressors are equipped with: oil filter, oil hole, exhaust with pressure gauge interface, suction cut-off valve, suction filter, sight glass. The motor of the semi-hermetic compressor is covered with an insulating layer to prevent the penetration of lubricating oil and refrigerant. The cooling of the motor is extremely important. Generally speaking, the most suitable temperature of the motor winding is 70 ℃ to 90 ℃, and the maximum temperature cannot exceed 100 ℃. The load-bearing capacity of the motor depends on its operating temperature. If the insulation layer withstands high temperatures, the motor may be damaged. Excessive voltage fluctuations, missing phases, motor stalls, and poor heat dissipation can increase additional power consumption, resulting in a sharp rise in motor temperature. Compressor cooling Air-cooled compressor: It is cooled by the air flow of the condenser fan, or an independent fan with sufficient air volume can be used for cooling. The cooling air must be blown directly to the compressor. Return-air cooling compressor: In the return-air cooling compressor, the motor is cooled by the gas refrigerant passing between the stator and the rotor. In R22 low temperature applications, additional injection liquid cooling is usually used to ensure that the exhaust temperature is within the allowable range. Excessive exhaust temperature will cause a series of problems, such as causing the lubricant to deteriorate or form acidic substances, which can cause motor or bearing failure. The lower the evaporation temperature, the higher the exhaust temperature. Install shock absorption The compressor should be installed with four shock-absorbing pads, which can absorb and buffer the starting shock of the compressor. During operation, noise and vibration can be prevented from being transmitted to the compressor base and spreading further. The compressor supported by the shock-absorbing pad requires flexible flexible hoses (shock absorbers) to be installed on the suction and exhaust pipes to prevent the vibration and noise transmitted by the compressor through the refrigerant pipeline. The shock tube should be as close as possible to the compressor and as parallel as possible to the crankshaft. Pipeline connection The installation of pipelines in refrigeration equipment requires great care and a high degree of cleanliness. In principle, only pipelines with clean, dry, no scale, no rust, and no phosphate layer should be used. In order to prevent the generation of dirt in the welds in the pipeline, the degree of material melting must be controlled as much as possible. The lubricating oil carried by the refrigerant must be returned to the compressor as quickly and continuously as possible, but an oil trap or check valve should be used to prevent the lubricating oil and refrigerant from returning to the cylinder head through the exhaust pipe. It is also important that the minimum velocity of the gas in the suction pipe and exhaust pipe should comply with the regulations to ensure oil return. A "U" shaped oil return bend is set at the bottom of the suction riser, and an additional one is added every 5 meters. Dry filter and humidity indicator Do not use a desiccant such as potassium chloride that will absorb a large amount of moisture and become liquid. It is recommended to use porous block-shaped desiccant to absorb moisture and acid to prevent dirt and metal debris. The installation of the filter drier must be carried out after the second evacuation process. The sight glass of the humidity indicator should be installed in the easy-to-see part of the liquid pipeline to achieve the purpose of checking the refrigerant flow. Suction pipe filter To avoid compressor failure, all impurities (dirt, welding scale, borax, metal shavings, etc.) must be removed from the system before operation. Many impurities are very small and can enter the suction side of the compressor through a microporous filter. The compressor suction filter will also be blocked for other reasons, and even a large pressure drop will cause damage. Oil separator When installing the oil separator. It must be filled with lubricating oil until the overflow valve starts to open, and the oil quantity is maintained in the oil separator, otherwise the lubricating oil in the compressor will be taken out by the oil separator and reduced. Electrical connections Before making electrical connections, check whether the voltage, phase number, and frequency of the power circuit used match the data on the compressor nameplate. In addition, it is necessary to pay attention to the sign of the voltage connection conversion mode related to the motor starting mode on the nameplate. When determining the motor connection (△ or Y). Please pay attention to the sign of the voltage connection conversion mode on the nameplate and the possible starting mode △ or Y. Vacuum (dry) The system must be evacuated after the leak test. The vacuuming capacity will be significantly reduced due to the narrow interface and connecting pipes. It should also be noted that because the vacuum gauge is usually located on the vacuum pump, its indication value is difficult to match the vacuum degree at the end of the system, so additional vacuuming time should be added. In order to achieve the same degree of vacuum in all parts of the system. Note: It is not allowed to start the compressor under vacuum and conduct high voltage test and insulation strength test to avoid damage to the motor. Refill of lubricating oil Generally new semi-hermetic compressors have been filled with a sufficient amount of lubricating oil required for normal operating conditions, the so-called initial filling of lubricating oil. At the initial stage of compressor start-up or operation, part of the lubricating oil leaves the compressor due to mixing with the refrigerant, and is distributed in some parts of the system according to the system structure and cannot be completely returned to the compressor. At the initial filling, the lubricant that cannot be returned to the compressor must be taken into account. Observe the oil level in the sight glass of the compressor, and avoid excessive filling when adjusting the oil level, because too high oil level will affect the normal operation of the compressor. Spray liquid cooling and exhaust temperature protection device When the semi-hermetic compressor is used for refrigerant R22 at low temperature, an additional liquid cooling device is required. It controls the opening / closing of the valve and the amount of liquid injection by sensing the exhaust temperature of the cylinder head through its temperature sensing package, thereby controlling the exhaust temperature within the allowable temperature range. Operating conditions or system layout may generate high-temperature and high-pressure gas, which may cause carbonization of the lubricating oil or decomposition of the refrigerant, causing the compressor to operate abnormally or even malfunction. At this time, an exhaust temperature protection device should be installed. Crankcase heater If, due to the layout of the system or the position of the compressor, there is a possibility that a large amount of liquid refrigerant or lubricant oil absorbing refrigerant exists in the compressor, a heating device for the lubricant oil in the crankcase must be used. The higher temperature generated by the heater causes the refrigerant to continuously vaporize, avoiding problems with the supply of lubricating oil. High voltage controller In order to operate the refrigeration system safely and reliably, the refrigeration system must be equipped with a high-pressure controller. The high-pressure controller must be connected to the high-pressure interface of the compressor or any point on the exhaust pipe. However, never connect the high-voltage controller to an interface that may be cut off. Low voltage controller The low-pressure controller on the refrigeration equipment is used to: 1. Ensure the working range of the compressor; 2. Prevent the pressure from being too low (lack of refrigerant); 3. Stop when the pump-down cycle is terminated. Hydraulic controller The oil pressure controller can detect the pressure difference between the oil pump outlet and the crankcase. When the pressure difference does not reach the minimum tolerance, the compressor should stop running within 1-2 minutes. All semi-hermetic compressors with oil pumps should be equipped with differential pressure controllers. Oil pressure of oil pump The normal oil pressure is approximately 1.05 to 4.2 bar higher than the crankcase pressure. If you need to measure the oil pressure, you can connect a pressure gauge to the needle valve on the side of the oil pump tee, and connect the other pressure gauge to the tee on the crankcase or the compressor suction cut-off valve. Change lubricant The appearance of refrigeration oil should be clear and transparent. If the dirt is particularly serious, it is recommended to disassemble the compressor chassis and clean the crankcase and chassis. The compressor must be evacuated before it is started again. If it is not necessary to remove the chassis, lubricating oil can be released from the oil filler hole or the air channel of the return air cooling compressor where the filter or crankcase heater is installed. When draining oil from the filler hole, first close the compressor suction valve, reduce the crankcase gauge pressure to about 0.1 bar and close the exhaust shut-off valve. Carefully loosen the oil hole bolts to reduce the residual pressure in the crankcase. Leakage-replace the gasket If the equipment leaks after installation, first use a torque wrench to re-tighten the bolts. Torque wrenches prevent bolts from overtightening and slipping. If re-tightening the bolts does not stop the leakage, replace the seals on the cylinder head, globe valve, chassis, and compressor box cover. However, if the compressor cannot be completely evacuated after replacing the gasket, it is recommended not to replace the gasket. After the installation, replacement or repair of the machine head, cylinder head, valve plate and similar components, in principle new seals must be used. In any case, the compressor must be evacuated before starting again. Valve plate and valve plate group Refrigerant liquid and debris circulating with the refrigerant can damage the valve plate with the suction and discharge reeds and the stopper. The valve disc set will malfunction, be damaged or be destroyed. Damaged or unable to work normally will reduce the output power of the compressor. If the valve is damaged, the compressor will stop. The leakage of the working valve (exhaust side) can be checked by the following methods: Connect a suction pressure gauge to the pressure gauge port of the suction shut-off valve. Close the suction cut-off valve to cut off the suction pipe path. Start the compressor to make the pressure gauge display -0.5bar vacuum pressure, then stop and open the suction cut-off valve to increase the gauge pressure to 0bar, and then close the cut-off valve. If the pressure continues to rise within one minute, it means that the working valve is not closed tightly. It is recommended to replace the entire valve plate and not just the valve disc. Note: A leak in the suction shut-off valve may also cause the pressure to rise. Refrigeration equipment with an oil separator should close the oil return valve during the above test. Oil pump repair Once it is confirmed that the oil pump is not working properly, it must be replaced. The oil pump is fixed on the compressor bearing cover by 6 bolts, the center of which is aligned with the center of the bearing sleeve or bearing cover. The oil pump can run forward and reverse. After long-term operation, the conversion mechanism of the oil pump may be blocked by wear, corrosion and dirt. Therefore, the operation cannot be reversed. Do not energize the oil pump during maintenance. Motor burned out Burnout is rare, but if high-temperature and high-pressure gas, residual corrosives, acidic substances and decomposed lubricating oil are present in the equipment, the result (unless the working valve or operating mechanism is damaged first) will eventually cause damage to the built-in motor. Refrigeration equipment that damages the compressor due to motor burnout cannot be cleaned rashly. Otherwise, the replaced built-in motor will be burned again due to the influence of the residue left in the device by the previous motor burn. Two-stage compressor The compression process of a two-stage compressor is divided into a high-pressure stage and a low-pressure stage. In a 6-cylinder two-stage compressor, four cylinders are low-pressure stages, and two cylinders are high-pressure stages. The refrigerant gas returned from the evaporator first enters the low-pressure cylinder, and is compressed by the low-pressure cylinder to form a pressure between the condensation pressure and the suction pressure. These gases have a higher temperature and a higher pressure at this time, enter the medium-pressure mixed liquid pipe, and after mixing with the low-temperature refrigerant from the liquid pipe through the intermediate cooling expansion valve and the economizer, enter the motor cavity to pass and cool the motor ( Therefore, the pressure in the motor cavity and crankcase is the intermediate pressure). Then enter the high-pressure cylinder to compress to high-pressure gas and discharge to the condenser.

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