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Small cold storage common troubleshooting

2017/11/16

Small cold storage, including mobile cold storage, the capacity is generally below 100 tons. Cold storage evaporator using exhaust pipe or air-cooled combination of units by the compressor (water or air-cooled), throttling expansion valve and other components of a complete refrigeration system. Most compressors are semi-enclosed, large systems also have open type, smaller systems are fully enclosed. R22 refrigerant to common.

    Cold storage refrigeration system, the most common operating faults are generally: slow cooling temperature, system blockage caused by abnormal operating conditions or can not run.

   Cold storage temperature dropped slowly, mostly due to improper operation adjustment, of which the expansion valve is the most critical regulation. Expansion valve opening degree is small, the flow of refrigerant through the less pressure is low; expansion valve opening degree, the refrigerant flow through the more pressure is high. According to the thermal properties of the refrigerant, the lower the pressure, the lower the corresponding temperature; the higher the pressure, the higher the corresponding temperature. According to this law, if the expansion valve outlet pressure is too low, the corresponding evaporation pressure and temperature is too low. However, due to reduced flow into the evaporator, the pressure is reduced, resulting in slow evaporation, cooling capacity per unit volume (time), cooling efficiency decreased. Conversely, if the expansion valve outlet pressure is too high, the corresponding evaporation pressure and temperature are too high. Flow and pressure into the evaporator are increased, due to excess liquid evaporation, the excessive moisture gas (or even liquid) is sucked by the compressor, causing the compressor's wet stroke (liquid impact), so that the compressor can not work properly, resulting in a series of workers Bad condition, or even damage to the compressor. Expansion valve opening degree, should be based on the current temperature of the library to adjust, that is, the temperature corresponding to the library under the pressure adjustment. Such as the library temperature is -10 degrees, the cold storage of the evaporation temperature should be about 5 degrees lower than the library temperature, which is -15 degrees, the corresponding evaporation pressure of about 0.3MPa (absolute pressure). Due to the pressure loss, the adjustment pressure basically reflects on the suction pressure of the compressor.

    Adjusting the expansion valve must be carefully and patiently carried out. The pressure must be boiled (evaporated) by heat exchange between the evaporator and the bank and then passed through the pipe to the compressor suction chamber to be reflected on the pressure gauge, requiring a period of time. Each time the expansion valve is mobilized, it takes about 10 ~ 15 minutes to stabilize the expansion valve pressure on the suction pressure gauge. The adjustment can not be over-regulated. Compressor suction pressure is the main basis for adjustment of expansion valve parameters.

    Expansion valve performance is good or bad, a direct impact on its ability to regulate the operation of the logo. Usually prone to clogging the filter, the temperature sensor leakage and other failures. Resulting in the regulatory response is not sensitive, out of control or regulation can not be adjusted. Frosting occurs at the inlet of the expansion valve (or the valve cover also frosted), and the temperature of the inlet pipe is lower than normal temperature and even condensation. The suction pressure of the compressor is lower than the corresponding pressure under the temperature of the refrigerator, the operating temperature of the machine And the exhaust temperature is high, the cooling temperature drops slowly or not, enough to explain the expansion valve plugged, there is dirty or ice blocking phenomenon.

     Treatment: Turn off the main valve for liquid supply and turn on the compressor. When the suction pressure is stable below 0, turn off the compressor exhaust valve, and stop the compressor operation when the valve is closed. Open the inlet of the expansion valve, remove the filter after cleaning and install, and replace the infusion drying filter or filter, check the performance of the infusion solenoid valve recovery (inspection cleaning is completed). Open the compressor exhaust bypass port (the other is still receiving fluorine state), the boot operation, so that the total liquid supply valve to the compressor body of the air all from the exhaust bypass port until the suction pressure stabilized at 0 The following vacuum (exhaust is completed), close the exhaust bypass port, open the compressor exhaust valve and the total valve for the system to resume operation.

    If the expansion valve itself is working properly, it is only because of clogging caused by too much water or dirt in the system, causing serious ice blockage or dirty blockage, causing the system to work abnormally. The temperature of the liquid pipe in the expansion valve is lower than normal temperature and even Condensation, no temperature after the valve pipe reaction, the compressor suction pressure below 0, the machine operating temperature and exhaust temperature is high, or even percussion sound, cooling temperature does not drop, operating conditions harsh.

    The system is too much water, mainly because the maintenance of the vacuum is usually not complete; leakage caused by low pressure in the negative pressure to continue running and inhalation of moisture; shelved open time after the system is too long; mechanical resurgence sticky water; refrigerant refrigerant containing moisture Excess; water-cooled condenser caused by the rupture of the condenser. The reasons for excessive system fouling are mainly the deposition of iron oxide in the tube-and-tube evaporator and the water-cooled condenser and other contaminants in the system as a function of the working-substance circulation.

    To deal with the failure, the system of sewage and water removal operations can be carried out at the same time, the specific method: access compressor low pressure valve bypass port to put fluorine, when put to 0 gauge pressure, the system can be regarded as refrigerant has been put away. The lowest part of the evaporation tube in advance to open a diameter of the same bypass with the discharge pipe, and install the appropriate fluorine valve; condenser outlet (water-cooled condenser condenser tube rupture should be repaired or Replacement) should be installed with the three-way mouth and related valves. Open the compressor (water-cooled condenser water supply valve should be opened), inhaled from the suction inlet air, compressed by the compressor boost until the pressure rose to 1.2MPa gauge downtime, quickly full open evaporation tube The lowest bypass valve and condenser outlet three-way mouth, the compressed air along with the system dirt and water were quickly discharged from the high pressure and low pressure side (a smaller space cold bank drain outlet can be temporarily connected to the skin lead to the library In addition, pay attention to the skin can not be higher than the sewage outfall). When the system pressure close to 0, restart the compressor boost and sewage, so repeated several times, until the system of water and dirt to be confirmed all the discharge date. Immediately after the shutdown, replace the dry filter or new filter, clean the expansion valve filter and solenoid valve, remove the compressor suction filter, replace the compressor oil, close the drain pipe outlet valve and condenser outlet Mouth, compressor low pressure valve bypass port fluoride bottle, turn off the compressor exhaust valve, open the exhaust bypass port, the system should be opened to the other valves, start the compressor to run the system of vacuum and fluoride operation , Restore the system put into operation.

    Compressor compression efficiency test: turn off the compressor suction valve, open the exhaust bypass port (multi-purpose port), start the compressor operation, the compressor low pressure will soon form a vacuum, exhaust outlet vent Gradually smaller, and soon no more gas discharge, operating noise is gradually smaller, the exhaust bypass port is also no oil discharge, close the exhaust bypass port (multi-purpose port) After the compressor downtime low pressure vacuum will not be fast Rise, high and low pressure to wait 10-15 minutes after the balance, indicating that the compressor compression efficiency is good, the valve seal to meet the requirements. If the compressor exhaust vent has been gas discharge, or will bring out (spray) lubricating oil, sufficient to explain the compressor's poor compression, air tightness of the valve, the operating part of the cylinder and Oil ring wear gap is too large. Need to be repaired. This is the most basic, easiest and most practical way to test compressor compression efficiency and tightness tests.

    In addition, systematic oil-drain and air-release operations should be carried out on a regular or regular basis to enhance the heat exchange performance and cooling performance of heat exchangers. Due to the larger viscosity of the frozen oil, it is usually adsorbed on the inner surface of the pipe or vessel to form an oil film. Especially at the low pressure side (expansion valve outlet to compressor inlet), the viscosity of the oil is greater due to the lower temperature and the resulting oil film layer is of course larger, thus adding heat exchangers (evaporators and condensers) Thermal resistance, heat transfer performance, reducing the cooling effect. The more oil in the system, the greater the ills and therefore very detrimental to cooling. The presence of air or other non-condensable gases in the system can result in increased condensing pressure and temperature, increased power consumption, high compressor operating temperatures, heavy loads and reduced refrigeration efficiency. Exhaust pipe evaporator can be used to open the bottom of the sewage outfall discharge; chiller combined evaporator lowest outlet manufacturers are generally equipped with oil (dirty) mouth. Put oil and air operations should be carried out in the system downtime static, put air should also be selected when the temperature is low, so the effect will be better. There is no dedicated system to put air equipment, put the air generally choose the highest outlet on the high side. Cold storage of exhaust pipe and cooler finned tube, must be promptly (regular) to be defrosted, in order to ensure its good heat transfer. These are the most direct relationship with the cooling effect