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

I. Four - way Valve

(I) Function

(II) 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 pressure - difference switching action is used for commutation. 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, 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 a de - energized state, the pilot slide valve moves to the left under the drive of the compression spring. High - pressure gas enters the capillary tube and then into 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 slide valve 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 an energized state, the pilot slide valve 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 into 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 slide valve 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. The left and right valve bowls and the valve block move to the right, forming a heating cycle.

(III) 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.

(IV) Analysis of Common Quality Problems

1. Excessive Internal Leakage
   It is mainly caused by the insufficient tight fit between the main slide valve 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 moves and vibrates, accompanied by a "gurgling" sound.
   B. When the commutation speed of the piston and the main slide valve is slow, it is easily affected by the fluid, and a commutation sound occurs along with the vibration.
   C. During commutation, when the pressure is high, the friction is large, and the main slide valve vibrates and emits a commutation sound.
   D. During commutation, abnormal noise is generated by the sliding friction between the nylon main slide valve and the brass valve seat.
3. Poor Commutation (Gas Leakage) of the Four - way Valve
   A. System Reasons
   The basic condition for the four - way valve to commutate 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 slide valve 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 from the D connection of the four - way valve directly through the E and C connections to the S connection (the compressor's return pipe), causing the pressure difference to drop instantly, forming an instant gas - leakage state. If the compressor's exhaust volume 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.

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

(I) Function

(II) Valve Body Structure

1. The stop valve mainly consists of a valve core, a valve body, a valve core for air inlet (for low - pressure valve), a nut, and a connecting pipe. The lifting of the valve core, composed of a sealing ring, brass rod, etc., controls the degree of opening. 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. Differences between High - pressure and Low - pressure Valves
   The low - pressure valve has a charging port with a valve core for air inlet inside. It is mainly used for refrigerant charging during market maintenance.

(III) Processing Technology of the Stop Valve

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
   The CNC machining center is used. It features one - time clamping (completed integrally at one time) and short operation time. The production of one valve body 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 the 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. Heating of Copper Rod (Pre - process for Forging the Valve Body Blank)
   Medium - frequency induction furnace heating technology is adopted, which has a high 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 of stop valves that do not use this technology (achieved through flame heating + forging process).
4. Shot Peening Strengthening Treatment of the Valve Body Surface
   The purpose is to partially remove the residual internal stress from processing.
5. Fixing Methods of the Valve Body to the Valve Core
   There are three methods: necking + snap - ring, snap - ring, and necking. For the single - O valve core fixing method, necking + snap - ring is recommended. However, the fixing form of the snap - ring must be used, and it is not allowed to use only the necking form for fixation. For the double - O valve core fixing method, the necking form can be adopted.
6. Design of the Valve Port Diameter and Opening Degree of the Stop Valve
   The size of the diameter has a direct relationship with the opening degree and is a key parameter. The degree of opening can control the amount of refrigerant flow.

(IV) Key Quality Control Points

(V) 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
   designates the raw material grade as: Hpb59 - 1 extruded rod, rolled rod, or cold - drawn rod.
   B. Processing Control of Raw Material Blanks
   For the processing of 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. While using medium - frequency induction heating can provide better material temperature uniformity, manufacturers must be required to strictly implement the time interval for the blanks to pause in the air after reaching the heating temperature to ensure the stability of the valve body's crystal structure.
   C. Residual Internal Stress from Processing
   Stress - relief annealing treatment is required.
2. Poor Sealing
   A. Poor finish of the conical surface or non - 90 - degree angle and improper tight fit with the connecting pipe lead to leakage.
   B. Leakage of the valve body itself is mainly caused by cracks in the material and poor welding.
   C. Leakage is caused by the 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 is caused by the aging and cracking of the valve core's sealing ring.
   E. Leakage is caused by the valve core being pushed out by the system pressure due to insufficient or no necking of the valve body.
   F. Leakage is caused by poor sealing of the air - inlet valve core of the high - pressure valve. When tightening the air - inlet valve core, 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 inner hexagon of the valve core being worn due to excessive torque, making the valve core unable to be opened or closed tightly.
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 rings inside the four - way valve body and the high - (low - ) pressure valve body due to heat.

III. Check Valve

(I) Function

(II) Structure of the Check Valve

(III) Main Quality Control Points

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

(IV) Analysis of Common Quality Problems

1. Abnormal Noise
   A. 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 is small and the valve seat opening is large, resulting in a large clearance when the valve core stays at the valve seat opening. 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 generate an impact sound.
   B. There are 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 are inserted too deeply, resulting in a whistling sound. Excessive insertion will cause the air flow to directly blow against the valve core and generate resonance.
2. Excessive Leakage
   It is mainly due to the large fit clearance between the valve core and the valve seat and the poor manufacturing and processing accuracy of the valve core.