This is a pressure-controlled valve without a sensing bulb:

The correct answer is the AXV, or Automatic Expansion Valve. This device regulates refrigerant flow based on the pressure within the system rather than relying on a sensing bulb or remote sensor. It automatically adjusts the flow of refrigerant to maintain a desired pressure in the evaporator, ensuring that it operates efficiently.

In HVAC systems, the AXV continuously monitors the pressure of the refrigerant and adjusts the opening of the valve to maintain a consistent flow without needing a separate sensing element like those found in thermal expansion valves (TXV) or electric expansion valves (EEV). This characteristic makes AXVs particularly useful in systems where simplicity and reliability are prioritized.

Understanding the operational mechanics of the AXV is crucial for effectively managing refrigerant flow and maintaining optimal system performance. This can also lead to enhanced energy efficiency and reduced wear on the components of an HVAC system.