Refrigeration expansion valve refrigeration system is an important component for a variety of freezing, refrigeration, refrigeration system automatically adjusts. Generally installed between the reservoir and the evaporator, the refrigerant expansion valve through the evaporator end of the superheat changes to control the valve flow, high pressure liquid refrigerant throttling decompression, to ensure that the pressure difference between the condenser and evaporator , So that the liquid refrigerant in the evaporator at the required low pressure evaporation endothermic, so as to achieve the purpose of refrigeration and buck. At the same time, the gaseous refrigerant in the condenser radiates heat and condenses at a given high pressure to adjust the flow rate of the refrigerant fed into the evaporator so as to adapt to the change of the heat load of the evaporator and prevent the under-utilization of the evaporator area and the knocking of the cylinder Phenomenon, the refrigeration unit more effective operation. Throttling agencies have the following types: manual expansion valve, float expansion valve, thermal expansion valve. First, the manual expansion valve Manual expansion valve structure and the normal cut-off valve is similar, but it is a needle valve cone or â…¤ shaped notch cone. Stem with fine thread, the hand wheel rotation, the valve can be opened slowly or small base to ensure good regulatory performance. Its salient features are not easily broken. Managers should manually adjust the opening of the expansion valve according to the change of the heat load of the evaporator and other factors, so that the operation management is troublesome and requires high experience. At present, the automatic expansion valve is mostly used, and the manual expansion valve is only used On the bypass pipe, as a secondary role. Second, the float-type expansion valve Float-type expansion valve used for full liquid evaporator, the evaporator requires liquid level to maintain a certain height, is in line with the characteristics of float-type expansion valve. According to the flow of liquid refrigerant different, float-type expansion valve can be divided into two kinds of straight-through and non-straight-through, they have their own advantages and disadvantages. Straight-through expansion valve to the evaporator liquid, first all through the float chamber, and then through the liquid balance pipe into the evaporator, so it has a simple structure, but the float chamber liquid level fluctuations, the impact on the spool Force is also larger, easy to damage the spool; times, but also need a larger caliber balance tube. Non-through-type float expansion valve, the valve mechanism in the floating room, the throttle after the refrigerant does not pass through the float room, but directly into the evaporator along the pipeline, so the floating chamber liquid level smooth, but in the construction and installation complex. Third, the thermal expansion valve is different from the float expansion valve, it is not through the control of liquid level, but the outlet of the evaporator to control the degree of superheat of gaseous refrigerant to control the flow of refrigerant into the evaporator. Because a portion of the evaporator area must be used to overheat the gaseous refrigerant, it is widely used in all non-full-liquid evaporators in air conditioners or cryogenic systems, especially Freon refrigeration systems. Thermal expansion valve due to different ways of balancing, or evaporation pressure leads to the lower cavity within the different ways, there may be two types of internal and external balance. Thermostatic expansion valve installation position must be near the evaporator, the valve body should be placed vertically, can not be tilted, but can not be reversed installation. The main is the installation of temperature package, usually wrapped around the suction tube, close to the wall, tightly packed, the contact should be removed oxide scale clean, exposing the true nature of the metal pipe, if necessary, can be coated with a layer of aluminum paint as a protection Layer to prevent rusting. Refrigeration Expansion Valve Commissioning Techniques and Troubleshooting 1 Overview As we all know, the thermal expansion valve is one of the four major components of a refrigeration system. It is responsible for reducing the refrigerant pressure from condensing pressure to evaporating pressure and controlling the refrigerant flow proportionally. A system of thermal expansion valve will have a direct impact on the performance of the entire system, so the timely removal of the thermal expansion valve in the work of the failure and the right choice, the life of the air-conditioning system, cooling effect, operating cost is of great significance . 2 thermal expansion valve works. Thermal expansion valve is by feeling evaporator outlet gaseous refrigerant superheat to control the flow of refrigerant into the evaporator.According to different balance, the thermal expansion valve is divided into external balance and internal balance, In the central air-conditioning system and more use of external balance by the sensor body, actuator, adjusting body and valve body. Work, the fixed outlet in the evaporator temperature sensor package outlet temperature sensor overheating, the pressure inside the temperature package, and spread to the capillary by the upper space in the diaphragm under the pressure of the flexible Transform the way the signal is passed to the thimble (actuator), which regulate the valve opening, control the flow of refrigerant. 3 Thermal expansion valve in the work of a few fault analysis 3.1 Thermal expansion valve plugging fault 3.1.1 The cause of the blockage Refrigeration system thermal expansion valve plugging failures are frequent, including "dirty plugging" and "ice plugging." Dirty plug The main reason is the existence of impurities in the system, such as welding slag, copper scrap, iron filings, fibers and so on. The reason for ice blocking is that the system contains too much moisture (moisture), the way to generate moisture is: 1) the system is not enough time to vacuum the system during installation, the pipes can not exhaust the moisture; pipeline connection Department of welding process is not good, there is leakage point. 2) The air in the connecting hose is not blown out of the hose when filling the system with refrigerant. 3) When the system is replenished with oil, enter the air. 3.1.2 The location of the blockage In general, dirty blockage occurs in the dry filter, the impurities in the system are intercepted by the filter, resulting in dirty blockage phenomenon. Occurred, the system first showed the return air temperature, superheat increased, serious problems, the system stops running, if not removed from the system of impurities, the system can no longer boot. Ice blockage typically occurs at the orifice of an expansion valve as it is the lowest temperature and smallest aperture throughout the system. As the system is not cooling, the overall system temperature rise, with the increase of temperature, ice block will gradually melt, and then restore the cooling capacity of the system, with the system as a whole again reduce the temperature again appears ice blocking phenomenon. Therefore, the ice jam is an iterative process. 3.1.3 How to eliminate the blockage So how to troubleshoot the blockage? For dirty block, if not very serious, for a dry filter on it. If very serious, it is necessary to re-clean the system of impurities in the pipeline, vacuum, refilling refrigerant. For a slight ice block, hot towel can be deposited in the ice block, if the degree of ice block is more serious, has affected the normal operation of the system, you have to replace the filter dryer, re-off the system of water pipes, vacuum, Refill refrigerant. 3.2 temperature package fault 3.2.1 temperature package common cause of failure when the system appears when the expansion valve for a long time or less expansion valve is not small, superheat, undercooling is not correct, etc. The reason may be the temperature package There has been a breakdown. Including: 1) temperature capillary bag rupture, so that the charge inside the thermos bottle missing, resulting in the correct signal can not be passed to the thermal expansion valve enforcement mechanism. 2) Temperature Wrapped bandaging location is not correct. 3.2.2 temperature package troubleshooting approach General situation temperature package as far as possible in the evaporator outlet horizontal section of the return pipe should be away from the compressor intake and close to the evaporator, but not vertical installation. When the horizontal air return pipe diameter is less than 7/8 "(22mm), the temperature sensing package should be installed at the top of the air return pipe, ie" one o'clock "of the air suction pipe. When the horizontal air return pipe diameter is more than 7/8" Warm package to be installed in the air return pipe axis below the horizontal axis at about 45 degrees, the suction pipe "3 o'clock" position. Because installing the temperature sensing package in the upper part of the suction pipe will reduce the sensitivity of the reaction and may cause excess refrigerant in the evaporator. Installing the temperature sensing package at the bottom of the suction pipe may cause disorder of the liquid supply because there are always a small amount Of the liquid refrigerant flows to the location where the temperature sensing package is installed, resulting in a rapid change in the temperature of the temperature sensing package. Installation, the temperature package need to use copper wrap, back to the pipe surface to rust, if it is steel, rust painted silver paint surface to ensure that the temperature of the bag and back to the trachea good contact. Temperature package must be lower than the valve top membrane cavity, and the temperature of the package head to be placed horizontally or down, when the relative position higher than the membrane cavity, the capillary should be bent upward into a U-shaped, to avoid liquid into the membrane On the cavity. 3.3 Improper adjustment 3.3.1 Adjustment of the expansion valve about the concept Talking about adjustment, we must first understand several concepts (1) expansion valve overheating: thermal expansion valve at a certain degree of opening, the corresponding superheat known as the work of superheat That the thermal expansion valve superheat. Includes static superheat (SS) and open superheat (OS). (2) static superheat: thermal expansion valve in the open position, the minimum spring force, then the thermal expansion valve control the minimum superheat, called the static superheat SS. (3) dynamic superheat: the expansion valve hole is open, the valve opening with the outlet steam superheat increases and increases from the valve opening to the full open, the superheat increases the value of the value of dynamic superheat OS . 3.3.2 Expansion Valve Correct Adjustment Method (1) Before adjusting the thermostatic expansion valve, it must be confirmed that the refrigeration refrigeration abnormality is due to
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