Refrigeration system expansion valve (throttle valve) how to adjust and fault judgment？

‌ The expansion valves in the small cold storage refrigeration system installed by Xuelong refrigeration all adopt Danfoss thermal expansion valves, which have the characteristics of quick thermal adjustment, stable quality operation and long system smooth operation cycle。Among them, our engineering supporting expansion valve cooling capacity is small, use the import and export removable sodium fixed connection as shown in the figure below, the cooling capacity is slightly larger using welding interface, to prevent system leakage, the following introduces the corresponding thermal expansion valve principle and fault judgment。

Introduction to the principle and structure of expansion valve in cold storage refrigeration
The thermal expansion valve is one of the four components in the refrigeration system, which is responsible for reducing the refrigerant from the condensing pressure to the evaporation pressure under the corresponding working condition, and continuously maintaining the flow of the refrigerant under the working condition。The quality of the thermal expansion valve in a system will directly affect the operating performance of the whole system, so it is necessary to timely understand and eliminate the failure caused by the thermal expansion valve in the refrigeration system。

The thermal expansion valve controls the refrigerant flow into the evaporator by feeling the superheat of the gaseous refrigerant at the evaporator outlet.According to different balancing methods, thermal expansion valves are divided into external balance and internal balance。Working hours,The thermal envelope fixed on the evaporator outlet pipe senses the overheating temperature of the evaporator outlet,Pressure is generated in the thermal envelope,And pass through the capillary to the space above the diaphragm,Under the action of pressure, the diaphragm transmits the signal to the thimble (actuator) in an elastic deformation manner.,Thus regulating the opening of the valves,Control the flow of refrigerant。

2. Common faults and solutions
1, thermal expansion valve blockage failure
The blockage failure of thermal expansion valve in refrigeration system is often occurred, including "dirty blockage" and "ice blockage"..The main cause of dirty blockage is the presence of impurities in the system, such as desiccant damage, residual welding slag during installation, copper shavings, iron shavings, fibers, etc。The cause of ice blockage is that the system contains too much water and other media。
In general, dirty blockage occurs at the inlet of the expansion valve liquid filter, and the impurities in the system are blocked by the filter, resulting in dirty blockage of the filter。When it occurs, the system first shows that the suction pressure is reduced, the return temperature is increased, and the low pressure protection or cooling efficiency is decreased in serious cases。
Troubleshooting methods: Close the system liquid supply valve, start the refrigerator, close the compressor suction valve after running to the low pressure protection (or repeated several times), open the expansion valve for liquid supply, clean the filter screen, at the same time, it is recommended to replace the system filter dryer。
Ice blockage generally occurs at the throttle hole of the expansion valve, because this is the lowest temperature in the entire system, reaching the freezing point of water, causing blockage of the throttle aperture。The performance is that the refrigeration in the high temperature area is normal, the refrigeration capacity in the low temperature area is reduced, and the system can automatically recover after shutdown。Human intervention of the expansion valve (such as heating the expansion valve to work properly) can relieve the ice blockage。
Elimination method: Replace the filter dryer repeatedly。Or choose good quality refrigerant。
2, the system conditions change, the expansion valve can not meet the system operation
According to the change of system running time and working condition, the adjustment degree of expansion valve is offset, which needs to be adjusted by maintenance personnel and customers。
Before adjusting the thermal expansion valve, it must be confirmed that the refrigeration anomaly is caused by the thermal expansion valve deviating from the optimal operating point, and not due to improper defrosting adjustment, refrigerant loss, filter dryer blockage, compressor suction and exhaust efficiency reduction, and other reasons (please consult the Shillon refrigeration service personnel to confirm).。At the same time, ensure that the sampling signal of the temperature sensing bag is correct and that the installation position of the temperature sensing bag is not removed from the upper end of the air return pipe。
Open the expansion valve adjusting port cover bolt, adjust the screw with a tool: turn clockwise (that is, increase the spring force, reduce the thermal expansion valve opening degree), so that the flow rate is reduced;On the contrary, if the superheat is too large, that is, the liquid supply is insufficient, the adjusting screw can be rotated in the opposite direction (counterclockwise) to increase the flow rate。The adjustment process should be carried out slowly, because the system flow is slow to change, each adjustment, to observe the effect, and record the original position, easy to restore the original system。
3. The spool and temperature sensing bag are damaged
If the above faults have been eliminated, the only possibility is that the expansion valve is organic damage。
Common: Temperature packet leakage, can not automatically adjust according to the superheat。Spool ball damage or stuck, spring deterioration, etc., need to contact Sheron refrigeration after-sales personnel, repair telephone: 0451-84859422。