How Hot-air Bypass Solenoid Valve Works in Refrigeration

Solenoid valve is widely applied on pipelines of liquid, air suction and hot air in refrigeration system. Liquid pipeline can cut off liquid flow when machine halts to avoid liquid state refrigerant enters evaporator and compressor. The connection of exhaust pipe and return air pipe via solenoid valve makes a function of bypass, which is to regulate refrigeration load.

Structure of Solenoid Valve

Figure below clearly shows what a solenoid valve composes. There are three major parts including magnet coil, valve plug and valve block. Based on actual needs, there are normally open and normally close types available. When magnet coil is powered on, it will valve block will perform open or close actions driven by valve plug.
 

Connection of Solenoid Valve

The generally way of connection in Shini is to drive gas state refrigerant from high temperature and pressure of bypass exhaust pipe to the low pressure side. The effect of bypass varies according to different pipeline connections. The connection to high pressure side of bypass solenoid valve can be at random in pipelines prior to enter condenser. And one connection to low pressure side is located in pipelines at the exit of thermal expansion valve. In this way, hot air from high pressure side enters evaporator thus evaporation load can be increased to reduce the possibility of evaporator frost damage due to pressure down. Meanwhile, evaporator outlet temperature and pressure can be increased to improve compressor operation in low temperature.

Another connection is located in air suction pipe and flow will return to compressor through air suction pipe without passing evaporator. Therefore, hot air of high temperature and pressure will mix gas state refrigerant of low temperature and pressure from evaporator and compressor air suction pressure can be raised. At the same time negative effect will come out that too high air suction temperature will damage compressor and may shorten its lifespan. For the second bypass way, it is necessary to add a liquid injecting cooling solenoid valve, which is able to lower compressor air suction temperature when temperature is too high.

Application Occasions of Solenoid Bypass Valve

What are the models that are equipped with hot-air bypass valve? For models used to precisely control water temperature, hot-air bypass valve is necessary to control evaporator load and avoid frequent compressor start/stop. If the load is free of control, evaporator pressure will decrease as water temperature drops. And finally machine stops working when evaporation temperature reaches set value of anti-freezing switch (Shini Chillers set anti-freezing temperature at 4℃). There is three minutes of delay for compressor startup each time and during this time water temperature in tank can not be controlled and will keep rising as load increases. For re-launch of compressor, it requires a while of refrigeration to cool down water in tank. Therefore, if users want to control water temperature precisely without adopting bypass valve to regulating compressor, machine will fail to meet the actual demands.