Final answer:
Thermostatic expansion valves are designed to maintain constant pressure of a given amount of gas at a constant temperature.
Step-by-step explanation:
Thermostatic expansion valves are designed to maintain constant pressure of a given amount of gas at a constant temperature. This is achieved by regulating the flow of refrigerant into the evaporator coil of an air conditioning or refrigeration system. The valve adjusts the size of its opening based on temperature changes to maintain a consistent pressure within the system.