Which device modulates refrigerant flow based on superheat or temperature?

Which device modulates refrigerant flow based on superheat or temperature?

• A. Fixed orifice
• B. Capillary tube
• C. Manual valve
• D. Thermostatic expansion valve modulates refrigerant flow based on superheat or temperature.

Answer: (D)

The device is designed to automatically meter refrigerant in response to the evaporator load by sensing temperature and superheat. A sensing bulb attached to the evaporator outlet detects the refrigerant temperature; the pressure from that bulb acts on a diaphragm to adjust the valve opening. If the superheat is too low, the bulb pressure drops and the valve opens more, allowing more refrigerant into the evaporator. If the superheat rises toward the setpoint, the bulb pressure increases and the valve closes slightly, reducing flow. This feedback keeps the evaporator working with the right amount of refrigerant so most of what leaves the evaporator is vapor, preventing liquid from returning to the compressor and maximizing efficiency. Fixed orifice and capillary tubes provide a constant, unadjustable flow and don’t respond to evaporator conditions. A manual valve requires operator control and also doesn’t automatically regulate superheat.

The device is designed to automatically meter refrigerant in response to the evaporator load by sensing temperature and superheat. A sensing bulb attached to the evaporator outlet detects the refrigerant temperature; the pressure from that bulb acts on a diaphragm to adjust the valve opening. If the superheat is too low, the bulb pressure drops and the valve opens more, allowing more refrigerant into the evaporator. If the superheat rises toward the setpoint, the bulb pressure increases and the valve closes slightly, reducing flow. This feedback keeps the evaporator working with the right amount of refrigerant so most of what leaves the evaporator is vapor, preventing liquid from returning to the compressor and maximizing efficiency.

Fixed orifice and capillary tubes provide a constant, unadjustable flow and don’t respond to evaporator conditions. A manual valve requires operator control and also doesn’t automatically regulate superheat.