Introduction and Troubleshooting of Refrigeration Expansion Valve ã€ä¸Šã€‘ The refrigeration expansion valve is an important part of the refrigeration system and suitable for automatic adjustment of various refrigeration, refrigeration and refrigeration systems. 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 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 and the float expansion valve is different, it is not by controlling the 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 where the temperature is lowest throughout the system and the aperture is smallest. 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. Introduction and Troubleshooting of Refrigeration Expansion Valve [Next] 3.1.3 How to eliminate the blockage How to eliminate the blockage problem? For dirty blockage, if it is not serious, change a dry filter. 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 causes 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 probe and the back of 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 Correct Adjustment of Expansion Valve (1) Before adjusting the thermostatic expansion valve, it must be confirmed that the refrigeration refrigeration abnormality is caused by the thermal expansion valve deviating from the optimum working point, not because of freon leakage, clogged filter, , Fans, belts and other causes caused. At the same time, we must ensure the correctness of the temperature package sampling signal, the temperature sensing installation location must be correct, absolutely can not be installed directly below the pipe to prevent the bottom of the tube oil and other factors affect the temperature sensing package the correct temperature. (2) Thermal expansion valve adjustment Note: The thermal expansion valve adjustment work must be carried out in the normal operation of the refrigeration unit. As the evaporator surface can not be placed thermometer, you can use the compressor suction pressure as the saturated pressure within the evaporator, look-up table to get the approximate evaporation temperature. With a thermometer to measure the temperature of the return pipe, compared with the evaporation temperature to check the superheat. Adjustment, if you feel too hot, you can turn the adjustment screw clockwise (that is, increase the spring force to reduce the thermal expansion valve opening), so that traffic decreases; the other hand, if you feel too much heat, That is, the lack of fluid, you can turn the adjustment screw in the opposite direction (counterclockwise), so that traffic increases. Due to the actual work of thermal expansion valve temperature sensing system there is a certain degree of thermal inertia, the formation of signal lag, the basic stability of the operation before the next adjustment. Therefore, the entire adjustment process must be patient and meticulous, adjusting the number of turns of the screw should not be too fast too fast. (3) Thermal expansion valve specific adjustment steps: 1) downtime. Insert the probe of the digital thermometer into the insulation at the return air inlet of the evaporator (corresponding to the temperature sensing package). Connect the pressure gauge to the tee of the compressor low pressure valve. 2) Turn on the compressor, let the compressor run for more than 15 minutes, enter the steady running state, make the pressure indication and the temperature display reach the stable value. 3) read the temperature of the digital thermometer T1 and the pressure gauge corresponding to the pressure measured by the temperature T2, superheat the difference between the two readings T1-T2. Note that both readings must be read at the same time. Thermal expansion valve superheat should be between 5-8 ℃, if not, then make the appropriate adjustments. Adjustment steps are: first remove the thermal expansion valve protective cover, and then turn the adjustment screw 2-4 laps, the system is running stable, re-reading, calculate the degree of superheat, is in the normal range, if not, repeat the previous operation until it meets Requirements, the adjustment process must be careful. 4 the correct choice of thermal expansion valve 4.1 the correct choice of thermal expansion valve thermal expansion valve matching the performance of the entire system play an important role in the correct choice of the thermal expansion valve will make maximum use of the evaporator and The evaporator is always matched to the thermal load. 4.2 thermal expansion valve and the system does not match the phenomenon: do not match, it will make the system when the flow of refrigerant more than a few hours, resulting in thermal expansion valve cooling time is small, when the cooling capacity is too small, will make the evaporator for Liquid shortage, resulting in excessive heat, the system performance will have an adverse effect.When the cooling capacity is too large, it will cause shocks, intermittent to make the evaporator overdose, resulting in the compressor suction pressure fluctuations, or even Liquid refrigerant enters the compressor and causes liquid strike (wet stroke) 4.3 Basis of selection: Select according to the type of refrigerant in the refrigeration system, the evaporation temperature range and the evaporator overheating load. 4.3.1 Selection methods and general steps The following description of the expansion valve under the selection method. As the ceiling fans are used now, the general pressure drop evaporation are relatively large, so use the external balance of thermal expansion valve. According to the evaporation temperature and thermal expansion valve inlet and outlet pressure difference, check the supplier to the product selection table. The general steps are as follows: 1) to determine the system refrigerant model. 2) to determine the evaporator evaporation temperature, condensation temperature and cooling capacity. 3) thermal expansion valve inlet and outlet pressure difference. 4.3.2 For example, there is an evaporator coil (4DW4 / 10F-50x50.3A), R407C refrigerant, 96KW cooling capacity, 8 ° C evaporation temperature and 50 ° C condensation temperature. Choose what type of thermal expansion valve Danfoss products as an example). First determine the differential pressure across the inlet and outlet of the expansion valve P Δ. In the formula: P k is the condensing pressure. P 0 is the evaporation pressure. 1 P Δ is the pressure drop of the copper tubing. 2 P Δ is the pressure drop across the dispenser and the separation capillary. P k (condensing pressure), P0 (evaporating pressure) can be found on the psychometric chart from the given known parameters. P k = 17.5 5 10 × P a, P0 = 6.5 5 10 × P a A) The pressure drop for the supply copper pipe, due to the coil selection software used, Pressure drop. It is therefore known that 1 P Δ = 0.0031 5 10 × Pa. Re-dispensing liquid pipette pressure drop empirical value 2 P Δ = 1 5 10 × Pa. "g When the refrigerant R407C, the cooling capacity of 96KW, the evaporation temperature is 8 ℃, the condensation temperature is 50 ℃, 1 P Δ is 10bar, select the model TDEZ26 thermal expansion valve (Danfoss products as an example) The stability of the device is related to the degree of superheat of the refrigerant at the outlet of the evaporator. Therefore, it is very important to timely and accurately troubleshoot the thermal expansion valve and correctly select the thermal expansion valve that matches with the system.