Commonly used to control the refrigerant level in the vessels

• A. Pressure relief valve
• B. Float switch/ Solenoid valves
• C. Thermostat
• D. Sight glass

Answer: (B)

Controlling liquid level in vessels is done by pairing a level-sensing device with an actuator that can open or close the refrigerant feed. A float switch sits at the desired level; as the liquid level changes, the float moves and switches the circuit. That switch then drives a solenoid valve to regulate flow into the vessel. When the level drops, the switch signals the valve to open and admit more refrigerant; when the level reaches the set point, the switch signals to close the valve, stopping flow. This combination provides automatic level control, keeping the vessel within the desired range.

A sight glass only lets you see the level and doesn’t regulate it, a thermostat controls temperature rather than level, and a pressure relief valve is a safety device, not a regulation method for liquid level.