This detailed diagram illustrates the internal structure and function of a thermostatic expansion valve (TXV), a key metering device in refrigeration and air conditioning systems. The valve controls refrigerant flow from the high-pressure liquid line (from the condenser) to the low-pressure expansion line leading to the evaporator, where the refrigerant changes into a boiling liquid/vapor mixture. The TXV comprises a body, piston (orifice), retainer, and flare nut for assembly. The thermostatic