Which device is commonly used to control refrigerant level in vessels by sensing the liquid level and actuating a valve?

• A. Float switch
• B. Sight glass
• C. Float switch/Solenoid valves
• D. Thermostatic expansion valve

Answer: (C)

The key idea is automatic level control using a level sensor that directly drives a valve. A float switch sits at the liquid surface and changes state as the level rises or falls. When it detects a set level, it signals a valve, typically a solenoid valve, to open or close and adjust the flow to bring the level back to target. This combination provides both sensing and immediate actuation, so the vessel maintains the desired liquid level automatically. A sight glass only shows the level; it doesn’t control anything. A thermostatic expansion valve regulates flow based on temperature/pressure, not the liquid level, so it isn’t used for level control. Therefore, the device pairing of a float switch with a solenoid valve is the standard solution for sensing the liquid level and actuating a valve.