Four-way valve structure and working principle
1. The electromagnetic four-way reversing valve is mainly used in the heat pump air conditioner, because there are mainly 4 pipes connected to it in the structure, so it is often called the four-way valve.
2. Its function is to change the function of the two parts of the air conditioner by changing the flow direction of the refrigerant in the system, and realize the switching of refrigeration, heating or defrosting functions.
3. The electromagnetic four-way reversing valve is composed of two parts, one part is the electromagnetic guide valve, and the other part 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 guide capillaries, and its structure is shown in the figure:
4. As can be seen from the figure, the solenoid guide valve is composed of a valve bowl, a spring, an iron core and an electromagnetic coil, etc., and there are four valve holes on the valve body that connect the guide capillaries.
5. When the refrigeration is running, the coil is not energized, and the iron core and the valve bowl move to the left together due to the thrust of the spring, at this time, the capillary D is connected with C (high pressure), and the capillary A is connected with B (low pressure), so as to promote the four-way reversing valve slider to move to the left, and the four-way valve E communicates with S, and D communicates with C;
6. When the heating is running, the solenoid guide valve coil is energized, the electromagnetic field attracts the armature to move to the right, the spring is compressed, and the iron core pushes the valve bowl to move right together, so that the capillary A and D are connected (high pressure), and the capillary B is connected with C (low pressure), so as to promote the slider of the four-way reversing valve to move to the right, D and E are connected, and C and S are connected.
7. The four-way reversing valve is composed of a valve body and 4 connecting pipes, 3 of the 4 pipes are on the same side, the middle is connected with the compressor suction pipe, and the remaining 2 are connected with the room, The external heat exchanger is connected, and the other one is connected on the other side, and the compressor exhaust pipe is connected, and the valve body is provided with a semicircular slider and two pistons with small holes, and the slider is used as a valve, can move left and right in the valve body, so that the two connecting pipes on the lower side are communicated through the two valve holes covered by the slider, and the other connecting pipe on the lower side communicates with the valve body through another valve hole, and the piston and the slider are connected together through the valve frame, and can move synchronously.
8. When the air conditioner is running for refrigeration, the solenoid valve coil is powered off, and the iron core pushes the valve bowl to move to the left, at this time, the capillary D and C are connected (high pressure), and the capillary A and B are connected (low pressure), because the capillary C and D are connected with the compressor exhaust pipe, and the capillary A is filled with high-pressure gas to form a high-pressure area, and the capillary A, B communicates with the suction pipe of the compressor to form a low-pressure area, at this time the piston moves to the left under the action of pressure, D communicates with C, the high-pressure refrigerant gas in the D tube enters the outdoor heat exchanger (as a condenser) through the C pipe to dissipate heat to the outside, and then enters the indoor heat exchanger (evaporator) through the capillary tube, and then enters the S tube from the E tube, and finally returns to the compressor to complete the refrigeration cycle, as shown in Figure 1:
When the air conditioner is heating and 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 the capillary A and D are connected (high pressure), and the capillary B and C are connected (low pressure), because the capillary A and D are connected with the compressor exhaust pipe, and the high-pressure gas is filled to form a high-pressure area, and the capillary B, c communicates with the suction pipe of the compressor to form a low-pressure area, at this time the piston moves to the right side under the action of pressure, D communicates with E, the high-pressure refrigeration gas in the D tube enters the indoor heat exchanger (as a condenser) through the E pipe to dissipate heat to the room, and then enters the outdoor heat exchanger (evaporator) through the capillary, and then enters the S tube from the C pipe, and finally returns to the compressor to complete the heating cycle, as shown in Figure 2:
Fault judgment of four-way valve in air conditioning system
1. Structural characteristics of four-way valves
1. Intermediate flow
It is not difficult to find from the structure of the four-way valve that when the main spool valve is in the middle position, as shown in the figure below, the three pipes of E, S and C are colluded 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 designing the intermediate flow is to relieve pressure when the main spool valve is in the middle position and avoid the air conditioning system from being damaged by high pressure.
2. The relationship between pressure difference and flow rate
The basic condition for the reversal of 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 frictional resistance f, otherwise, the four-way valve will not be reversed. The minimum operating pressure differential required for commutation is guaranteed by the flow rate of the system.
When the pressure difference between the left and right piston cavities (F1-F2) is greater than the friction resistance f, the four-way valve reversing starts, when the main spool valve moves to the middle position, the three pipes of the four-way valve E, S and C are conducted to each other, and the refrigerant discharged by the compressor will flow directly from the four-way valve D to the S pipe (compressor suction port) through the E and C pipes, forming an instantaneous gas cross-gas state. At this time, if the refrigerant flow rate discharged by the compressor is much greater than the intermediate flow loss of the four-way valve, the high and low pressure difference will not drop greatly, and the four-way valve has a large enough reversing pressure difference to make the main spool valve in place;
2. Possible reasons for insufficient refrigerant flow
1. Leakage of the air-conditioning system, resulting in insufficient refrigerant circulation in the system;
2. When the weather is very cold, the evaporation of refrigerant is not enough;
3. The four-way valve is poorly matched with the system, that is, the middle flow rate of the selected four-way valve is large and the system capacity is small;
4. The reversing time of the air conditioner. The general system is designed to change the direction of the four-way valve after the compressor is shut down for a certain period of time, at this time, the high and low pressure tends to be balanced, and the reversing stops in the middle position, that is, the four-way valve is not in place, and the main spool valve stops in the middle position.
5. The flow rate is insufficient when the compressor starts.
3. Reasons for poor reversing of four-way valves
1. The four-way valve coil is broken, short-circuited or the voltage does not meet the coil performance requirements, resulting in the valve core of the pilot valve not working;
2. Due to external reasons, the pilot valve part is deformed, resulting in the valve core cannot be operated;
3. The capillary tube of the pilot valve is deformed or blocked, and the flow rate is insufficient, and the pressure difference required for commutation cannot be formed;
4. The main valve body is deformed, and the piston part is stuck and cannot operate;
5. The refrigerated oil deteriorates or debris enters the system, and the piston of the four-way valve is stuck;
6. When the four-way valve is welded, the temperature is too high, and the internal parts are thermally deformed and cannot be operated;
7. The refrigerant leakage of the refrigeration system, the refrigerant circulation is insufficient, and the pressure required for commutation cannot be reached;
8. The compressor temperature is too high, the compressor cannot be well cooled due to refrigerant leakage and other reasons, and the exhaust temperature is too high, resulting in the deformation and jamming of the internal parts of the four-way valve or the reversing is not effective.
Overhaul and replacement of four-way valves
1. Four-way valve fault inspection steps
1. Check the power supply circuit of the four-way valve, the air conditioner is only supplied to the four-way valve when the heating is running, and the power supply inspection can determine whether it is the problem of the four-way valve or the control circuit.
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 energized, you should be able to hear the "click" sound generated when the iron core is sucked, and at the same time, you can also hear the "click" sound generated by the main valve reversing. When there is a suspicion that there is a problem with the coil, the resistance can be measured, and it should be about 1.4KΩ when it is normal, if the resistance value is small or infinite, it means that there is a short circuit or open circuit inside the coil.
When the coil is broken, the refrigeration is normal, but the heating cannot be made, and the evaporator of the internal machine is frosted.
When the coil is short-circuited, the machine heats up, which may burn out the fuse and make the whole machine unable to work.
3. Check the main valve, by checking the temperature of the refrigerant in and out of the main valve, you can judge whether the main valve is normal. When the air conditioner is running for refrigeration, D and C are connected and connected to the compressor exhaust port, E and S are connected to the evaporator return air (colder); during heating operation, D and E are connected to the compressor exhaust port (hotter), and E and C are connected to the condenser return air (colder);
4. When the four-way valve is crossed, the temperature difference between E, S and C may not be obvious, and the return pressure rises close to the exhaust pressure, do not rush to replace the four-way valve, first check whether the system is deficient in fluorine, because the lack of fluorine often leads to the pressure difference can not be established, and the four-way valve can not be reversed normally. If it is still not normal, you can gently tap the valve body, repeatedly turn on and off the power, and it can return to normal if it is slightly stuck. If it is still not normal, replace the four-way valve.
2. Precautions for replacing four-way valves
1. If the four-way valve is slightly stuck and the reversing is not effective, do not replace it rashly, you can first turn on and off the power of the coil repeatedly or tap the valve body lightly to force the sucking slider.
2. Before replacing the four-way valve, slowly release the refrigerant in the system, fill the system with nitrogen, and weld the four-way valve.
3. The four-way valve is often caused by impurities in the system, and the four-way valve is damaged, and the reason should be found, such as when the four-way valve is removed, observe the color of the refrigeration oil, if the oil has changed color and there are impurities, the system should be cleaned with high-pressure nitrogen, and the refrigeration oil should be replaced when necessary, otherwise the new four-way valve will be stuck again.
4. When welding, the system should be filled with nitrogen, the four-way valve should be wrapped in a wet towel, first welded to the exhaust pipe of the compressor, then welded to the compressor return pipe in the middle of the 3 parallel pipes, and finally welded both sides to take over with the evaporator and condenser.
5. After the welding is finished and the valve body is cooled, the system is filled with high-pressure nitrogen to detect the leakage to ensure that there is no leakage at each welding point and then vacuum and fluoride.
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