Basic Knowledge of Valve - type Components in Refrigeration Systems (Technical Sharing)

I. Four - way Valve

(1) Function

(2) Working Principle

1. Structure: It consists of a pilot valve, a main valve, and an electromagnetic coil. The pilot valve controls the main valve, and the commutation is carried out by pressure - difference switching action. The four connections of the four - way valve are as follows: the "D" port is connected to the compressor's exhaust pipe, the "E" port is connected to the low - pressure valve connection pipe, the "S" port is connected to the compressor's return pipe, and the "C" port is connected to the condenser pipe.
2. Working Principle:
   • When the electromagnetic coil is in the power - off state, the pilot spool moves to the left under the drive of the compression spring. High - pressure gas enters the capillary tube and then enters the piston chamber. On the other hand, the gas in the piston chamber is discharged. Due to the pressure difference at both ends of the piston, the piston and the main spool move to the left, making the E and S connections communicate, and the D and C connections communicate. The high - pressure fluid of the air - conditioner compressor flows into the right valve bowl chamber through the D and C capillaries, and the low - pressure fluid in the left valve bowl chamber flows into the compressor through the E and S capillaries. The left and right valve bowls and the valve block move to the left, forming a refrigeration cycle.
   • When the electromagnetic coil is in the powered - on state, the pilot spool moves to the right under the magnetic force generated by the electromagnetic coil, overcoming the tension of the compression spring. High - pressure gas enters the capillary tube and then enters the piston chamber. On the other hand, the gas in the piston chamber is discharged. Due to the pressure difference at both ends of the piston, the piston and the main spool move to the right, making the S and C connections communicate, and the D and E connections communicate. The high - pressure fluid of the air - conditioner compressor flows into the left valve bowl chamber through the D and E capillaries, and the low - pressure fluid in the right valve bowl chamber flows into the compressor through the C and S capillaries.

(3) Key Quality Control Points

1. Valve Body: Internal leakage, maximum operating pressure difference, minimum operating pressure difference, minimum operating voltage, and commutation flexibility.
2. Electromagnetic Coil: Temperature rise, insulation resistance, electrical strength, and inter - turn insulation of the coil.

(4) Analysis of Common Quality Problems

1. Excessive internal leakage: This is mainly caused by the insufficient tight fit between the main spool and the main valve seat.
2. Abnormal noise during commutation:
   • A: During the commutation process of the four - way valve, the fluid in the electromagnetic part is in a mixed state of liquid and gas, forming intermittent back - pressure. The piston vibrates during movement, accompanied by a "gurgling" sound.
   • B: When the commutation speed of the piston and the main spool is slow, they are easily affected by the fluid, and a commutation sound occurs along with the vibration.
   • C: During commutation, the higher the pressure, the greater the friction. The vibration of the main spool generates a commutation sound.
   • D: During commutation, the sliding friction between the nylon main spool and the brass valve seat produces an abnormal sound.
3. Poor commutation (gas leakage) of the four - way valve:
   • A: System - related reasons: The basic condition for the commutation of the four - way valve is that the pressure difference at both ends of the piston must be greater than the friction force. Otherwise, the four - way valve will not commutate. The minimum operating pressure difference required for commutation is ensured by the system flow rate. When the pressure difference between the left and right piston chambers of the four - way valve is greater than the friction force, the four - way valve starts to commutate. When the main spool moves to the middle position, the E, S, and C connections of the four - way valve communicate with each other. The refrigerant discharged from the compressor flows directly from the D connection of the four - way valve through the E and C connections to the S connection (the return pipe of the compressor), causing the pressure difference to drop instantaneously and forming an instant gas - leakage state. If the exhaust volume of the compressor is greater than the intermediate flow rate of the four - way valve, a sufficient commutation pressure difference can be established to make the four - way valve commutate in place. Conversely, if the exhaust volume of the compressor is less than the intermediate flow rate of the four - way valve, the minimum operating pressure difference required for the four - way valve to commutate cannot be established, and the four - way valve cannot continue to commutate and stops in the middle position, resulting in gas leakage.

II. High - and Low - pressure Valves (Stop Valves)

(1) Function

(2) Valve Body Structure

1. The stop valve is mainly composed of a valve core, a valve body, a valve stem (for low - pressure valve), a nut, and a connecting pipe. The lifting of the valve core, which is composed of a sealing ring, brass rod, etc., controls the opening degree. When the valve core is screwed to the bottom of the valve body, it closely cooperates with the conical surface at the bottom of the valve body to play a sealing role. The sealing ring in the figure is used to prevent refrigerant leakage.
2. The difference between high - pressure and low - pressure valves: The low - pressure valve has a charging port with a valve stem inside. It is mainly used for refrigerant charging during market maintenance.

(3) Processing Technology of Stop Valves

1. Material selection: The valve body material should be Hpb59 - 1 extruded rod, rolled rod, or cold - drawn rod, with stress - relief annealing treatment.
2. Processing method: CNC machining center. Its characteristics are one - time clamping (completed integrally at one time) and short operation time. The production of one valve body part can be completed within 10 - 14 seconds of operation. This reduces the defect of inconsistent position tolerances caused by secondary clamping, and the processing accuracy and consistency are better than those of other methods. In particular, the valve core must be processed by a CNC machining center to ensure that the form and position tolerance dimensional errors of the valve core are eliminated to the greatest extent, ensuring the reliability and quality of the valve core.
3. Copper rod heating (pre - process for forging the valve body blank): Medium - frequency induction furnace heating technology is adopted, which has a good degree of automation. The temperature control accuracy can reach within ±40℃, and the forging time can also be effectively controlled. This is quite different from manufacturers that do not use this technology (achieved through flame heating + forging process).
4. Shot - peening strengthening treatment of the valve body surface, aiming to partially remove the residual internal stress from processing.
5. The fixing methods of the valve body to the valve core: There are three methods, namely neck - down + snap - ring, snap - ring, and neck - down. For the single - O valve core, the neck - down + snap - ring fixing method is recommended. However, the snap - ring fixing form must be used, and it is not allowed to use only the neck - down form for fixing. For the double - O valve core, the neck - down form can be used.

   

6. Design of the port diameter and opening degree of the stop valve: The size of the port diameter has a direct relationship with the opening degree and is a key parameter. The opening size can control the amount of refrigerant flow. Currently, Midea's enterprise standard requires that the opening height of the stop valve should be greater than 1/2 of the port diameter.

7. Deburring and buffing processes are carried out on the parts where the inner surface of the valve and the valve core (the part with the "O" - ring) are in contact, fully ensuring the sealing performance (including reliability) and service life of the valve.

(4) Key Quality Control Points

(5) Analysis of Common Quality Problems

1. Cracking of the stop - valve body: Regarding the problem of valve - body cracking, there are mainly the following reasons:
   A. Selection of raw materials: Midea designates the raw - material grade as Hpb59 - 1 extruded rod, rolled rod, or cold - drawn rod.
   B. Processing control of raw - material blanks: For processing forged blanks, there are currently two heating methods used by manufacturers. One is direct flame spraying. This processing method has a large temperature - control fluctuation for the blanks, and it is difficult to ensure the uniform consistency of the organizational structure. When using medium - frequency induction heating, the material temperature uniformity is better. However, manufacturers must be required to strictly implement the time interval for the blank to pause in the air after reaching the heating temperature to ensure the stability of the valve - body's crystal - phase structure.
   C. Processing - residual internal stress: Stress - relief annealing treatment.
2. Inadequate sealing:
   A. Poor finish of the conical surface or non - 90 - degree angle that does not closely match the connection pipe without a valve, resulting in leakage.
   B. Leakage of the valve body itself, mainly caused by cracks in the material and poor welding.
   C. Leakage caused by poor fit between the valve core and the valve body. It also has a great relationship with the type of lubricating oil applied to the surface of the "O" - ring seal, the threaded part of the valve core, and the groove part.
   D. Leakage caused by aging and cracking of the valve - core sealing ring.
   E. Leakage caused by the valve - body neck - down not being in place or not being neck - down at all, and the system pressure pushing out the valve core.
   F. Leakage caused by poor sealing of the valve stem of the high - pressure valve. When tightening the valve stem, the manufacturer must be required to use a specified tightening torque (special torque wrench) because the magnitude of the tightening force has a great impact on the sealing performance.
   G. Phenomena such as the valve core not being able to be opened or closed tightly due to the wear of the inner hexagon of the valve core caused by excessive torque.
3. When welding the four - way valve body and the high - (low -) pressure valve body, if the weld is close to the four - way valve body or the high - (low -) pressure valve body (≤150mm), the four - way valve body and the high - (low -) pressure valve body should be immersed in water or wrapped with a wet towel soaked in water before welding to avoid damage to the sealing ring inside the four - way valve body and the high - (low -) pressure valve body due to heat.

III. Check Valve

(1) Function

(2) Structure of the Check Valve

(3) Main Quality Control Points

1. Flexible opening; 2. Leakage amount; 3. The gas - flow direction marked on the valve body should be consistent with the actual situation; 4. Good fit among the steel cone, the valve core, and the valve body, and the valve core should be free of burrs.

(4) Analysis of Common Quality Problems

1. Abnormal noise:
   A. The fit relationship between the valve core and the valve seat: The clearance between the valve seat and the valve is too large. During processing, the bottom of the valve - seat opening and the bottom of the valve seat are small, and the valve - seat opening is large. As a result, when the valve core stays at the valve - seat opening, the clearance is large. When the fluid passes through the two holes beside the valve seat, some refrigerant passes through this clearance, causing the valve core to resonate and produce an impact sound.
   B. Copper chips in the valve seat and burrs on the valve core.
   C. Oxide scale generated during welding.
   D. Uneven insertion of the capillary tube. Some insertions are too deep, resulting in a whistling sound. An overly deep insertion will cause the gas flow to directly blow onto the valve core and produce resonance.
2. Excessive leakage amount: Mainly due to a large fit clearance between the valve core and the valve seat and poor manufacturing and processing accuracy of the valve core.