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    Working principle of four way heat pump and air valve

    Author: Lucy source: Zhengxu air energy. Time: August 9, 2019. Click: 11751
    Starting with the action principle and structural characteristics of the four-way valve, this paper analyzes the causes of poor commutation (cross flow) in the market and the correct identification method, hoping to be helpful for the after-sales maintenance of air energy heat pump.

             Structure and working principle of four way valve

    It is often connected with the four-way valve in the pipeline.

    2. Its function is to change the function of the two air conditioners by changing the flow direction of refrigerant in the system, so as to realize the switching of refrigeration, heating or defrosting.

    3. The electromagnetic four-way reversing valve is composed of two parts, one is the electromagnetic guide valve, the other is the four-way reversing valve. The four-way reversing valve is controlled by the electromagnetic guide valve, and the two are connected by three guiding capillaries. Its structure is shown in the figure

     Structure and working principle of four way valve in air energy heat pump

    4. It can be seen from the figure that the electromagnetic guide valve is composed of valve bowl, spring, iron core and electromagnetic coil, and there are four valve holes connected with the guide capillary on the valve body.

    5. When the refrigeration is running, the coil is not electrified, and the iron core and valve bowl move to the left together due to the thrust of the spring. At this time, capillary tubes D and C are connected (high pressure), and capillary tubes a and B (low pressure), so as to push the slide of four-way reversing valve to move to the left, four-way valve e is connected with s, and D is connected with C;

    6. When the heating is running, the coil of the electromagnetic guide valve is energized, the armature is attracted by the electromagnetic field, and the spring is compressed. The iron core pushes the valve bowl to move right together, so that the capillary tubes a and D are connected (high pressure), and capillary tubes B and C are connected (low pressure), so that the slide block of the four-way reversing valve is moved to the right, D is connected with E, and C is connected with S.

    7. The four-way reversing valve is composed of a valve body and four connecting pipes. Three of the four connecting pipes are on the same side, and the middle connecting pipe is connected with the suction pipe of the compressor. The other two pipes are connected with the indoor and outdoor heat exchangers. The other connecting pipe is connected with the exhaust pipe of the compressor. The valve body is equipped with semicircular sliding block and two pistons with small holes. The sliding block can be left and right in the valve body By moving, the two connecting pipes on the lower side are connected through the two valve holes covered by the sliding block, the other connecting pipe on the lower side is connected with the valve body through another valve hole, and the piston and the sliding block are connected together through the valve frame, which can move synchronously.

    8. When the heat pump refrigeration is running, the solenoid valve coil is powered off, and the iron core pushes the valve bowl to move left. At this time, capillary tubes D and C are connected (high pressure), and capillary tubes a and B are connected (low pressure). Because capillaries C and D are connected with the compressor exhaust pipe, they are filled with high pressure gas to form a high pressure area, while capillaries A and B are connected with the suction pipe of the compressor to form a low pressure area Under the action, it moves to the left, and D is connected with C. the high-pressure refrigerant gas in tube D enters the outdoor heat exchanger (as the condenser) to dissipate heat to the outside through the C tube, then enters the indoor heat exchanger (evaporator) through the capillary tube, enters the S tube from the e tube, and finally returns to the compressor to complete the refrigeration cycle, as shown in Fig. 1

     Structure and working principle of four way valve in air energy heat pump

    When the heat pump is running, the solenoid valve coil is connected to the power supply, and the iron core drives the valve bowl to move to the right, so that capillary tubes a and D are connected (high pressure), and capillary tubes B and C are connected (low pressure). Because capillaries A and D are connected with the compressor exhaust pipe, they are filled with high-pressure gas to form a high-pressure area, while capillaries B and C are connected with the suction pipe of the compressor to form a low-pressure area Finally, it is connected with the heat exchanger tube (E) and then enters into the air cooler (d) through the heat exchanger tube (E), and then enters into the air cooler (d) as shown in Fig


     Structure and working principle of air energy heat pump and four way valve


    Fault diagnosis of four way valve in air energy heat pump system

    Structural features of one way and four way valves

    1. Intermediate flow rate:

    From the four-way valve structure, it is not difficult to find that when the main slide valve is in the middle position, as shown in the figure below, the three connecting pipes e, s and C are connected with each other, and there is a certain intermediate flow. At this time, the refrigerant in the high-pressure pipe of the compressor can directly flow back to the low-pressure pipe. The purpose of the design of the intermediate flow is that when the main slide valve is in the middle position, it can relieve the pressure and avoid the damage of the air conditioning system by high pressure.

    2. The relationship between pressure difference and flow rate

    The basic condition for reversing the four-way valve is that the pressure difference between the two ends of the piston (i.e. the pressure difference between the exhaust pipe and the suction pipe) (F1-F2) must be greater than the friction resistance F, otherwise, the four-way valve will not reverse. The minimum operating pressure difference required for reversing is guaranteed by the system flow.

    When the pressure difference between the left and right piston chambers (F1-F2) is greater than the friction resistance F, the reversing of the four-way valve starts. When the main slide valve moves to the middle position, the E, s, C three connecting pipes of the four-way valve are connected with each other. A part of the refrigerant discharged from the compressor will flow directly from the connecting pipe D of the four-way valve through the E and C connecting pipes to the s connecting pipe (suction port of the compressor), forming an instantaneous cross-talk state. At this time, the four-way flow rate of the compressor is lower than that of the four-way valve, if there is a large flow difference between the four-way valve of the compressor, if there is a large flow difference between the four-way valve of the compressor, if there is a large flow difference between the four-way valve of the compressor, if there is a large flow difference between the four-way valve of the compressor, if there is a large flow difference between the four-way valve of the compressor, if there is a large flow difference between the four-way valve of the compressor, if there is a large flow difference between the four When the operating pressure difference is low, the main valve will stop in the middle position, forming cross-over.

    2. Possible reasons for insufficient refrigerant flow

    1. The leakage of air energy heat pump system results in insufficient refrigerant circulation;

    2. When the weather is very cold, the refrigerant evaporation is not enough;

    3. The matching of four-way valve and system is not good, that is, the middle flow of the selected four-way valve is large and the system capacity is small;

    4 reversing time of air conditioner. The general system design is that the four-way valve will change direction after the compressor stops for a certain time. At this time, the high and low pressure tend to be balanced, and the reversing will stop at the middle position, that is, the reversing of the four-way valve is not in place, and the main slide valve stops in the middle position. At the next start-up, the flow is insufficient due to the effect of intermediate flow;

    5. The flow rate is insufficient when the compressor is started.


    Reasons for poor reversing of three-way valve and four-way valve:

    1. The spool of the pilot valve can not act due to the open circuit, short circuit or voltage of the four-way valve coil which does not meet the performance requirements of the coil;

    2. Due to external reasons, the pilot valve is deformed, resulting in the valve core unable to act;
        
    3. The capillary tube of pilot valve is deformed or blocked, and the flow rate is insufficient, so the pressure difference required for reversing cannot be formed;

    4. The main valve body is deformed and the piston is stuck and unable to move;

    5. Deterioration of refrigeration oil or impurities in the system, four-way valve piston stuck;

    6. When the four-way valve is welded, the temperature is too high, and the internal parts are thermally deformed and unable to act;

            7. Air energy heat pump System refrigerant leakage, refrigerant circulation is insufficient, can not reach the pressure required for commutation;

    8. The temperature of the compressor is too high. Due to the leakage of refrigerant and other reasons, the compressor can not be well cooled, and the exhaust temperature is too high, which causes the internal parts of the four-way valve to be deformed and stuck or the reversing is ineffective.


    Repair and replacement of four way valve

    Troubleshooting procedures of one and four way valves

    1. Check the power supply circuit of the four-way valve. The air conditioner only supplies power to the four-way valve during heating operation. Through the power supply inspection, it can be determined whether it is the four-way valve problem or the control circuit problem.

    2. Check the four-way valve coil. After confirming that the power supply is normal, check whether the coil is normal. When the coil is powered on, you should hear the "click" sound generated when the iron core is pulled in, and the "peep" sound generated by the reversing of the main valve. When it is suspected that there is something wrong with the coil, the resistance can be measured, which should be about 1.4k Ω in normal condition. If the resistance value is very small or infinite, it indicates that there is a short circuit or open circuit inside the coil. When the coil is open circuit, the refrigeration is normal, but the heating cannot be made, and the evaporator of the internal unit frosts. When the coil is short circuited and started to heat up, the fuse may be burned out and the whole machine can not work.

    3. Check the main valve. By checking the temperature of refrigerant in and out of the main valve, we can judge whether the main valve is normal. During the refrigeration operation of the air conditioner, D is connected with C and connected with the exhaust port of the compressor (), e is connected with s and connected with the return gas of the evaporator (relatively cold); during the heating operation, D is connected with E and connected with the exhaust port of the compressor (relatively hot), and E and C are connected with the return gas of the condenser (relatively cold);

    4. When the four-way valve is cross-linked, the temperature difference between E, s and C may not be obvious, and the return gas pressure increases close to the exhaust pressure. Do not rush to replace the four-way valve first. First, check whether the system is short of fluorine, because the lack of fluorine often leads to the pressure difference cannot be established, and the four-way valve can not normally reverse. At this time, appropriate amount of refrigerant should be injected, and then check whether the reversing is normal. If it is still not normal, gently tap the valve body and turn on and off repeatedly. If it is slightly stuck, it can return to normal. If not, replace the four-way valve.


    Notes for replacement of four way valve

    If the valve body is forced to turn off, the valve can not be changed if the valve is forced to stop.

    2. Before replacing the four-way valve, slowly drain the refrigerant in the system, fill the system with nitrogen, and weld the four-way valve.

    3. If the four-way valve does not work properly, it is often caused by impurities in the system. If the four-way valve is damaged, it can not be replaced immediately. The reason should be found out. For example, when removing the four-way valve, observe the color of the refrigeration oil. If the oil has discolored and there are impurities, the system should be cleaned with high-pressure nitrogen, and the refrigeration oil should be replaced if necessary, otherwise the four-way valve will be replaced soon It could get stuck again.

              4. When welding, the system should be filled with nitrogen, and the four-way valve should be wrapped with wet towel. First, the exhaust pipe of the compressor should be welded, then the air return pipe of the compressor in the middle of the three parallel pipes should be welded. Finally, the pipes connecting the evaporator and condenser on both sides should be welded.

              5. After the valve body is cooled after welding, fill in high-pressure nitrogen to detect the leakage of the system to ensure that there is no leakage at each welding point, and then vacuum and add fluorine.


              The reversing pressure difference of the four-way valve is directly related to the air displacement of the compressor. Please confirm the matching between the four-way valve and the system before use. This paper expounds the action principle, structural characteristics and reversing conditions of the four-way valve, analyzes the causes of poor reversing of the four-way valve and the general fault diagnosis and maintenance methods of the four-way valve, hoping to provide some help to the air energy heat pump maintenance technicians.
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