Function of a thermostatic expansion valve (TEV): Which description best captures its role in a refrigeration system?

Introduction / Context:
A TEV (TXV) is the most common metering device in comfort and commercial refrigeration. Understanding its control objective is essential for diagnosing issues like hunting, flooding, and starvation.

Given Data / Assumptions:

• Sensor bulb at evaporator outlet measures suction line temperature.
• Valve diaphragm senses bulb pressure against evaporator pressure and spring force.
• Target is to maintain a set superheat at the evaporator exit under varying load.

Concept / Approach:
By modulating the orifice opening in response to superheat, the TEV meters just enough refrigerant so the evaporator is well utilized (effectively filled) without allowing liquid carryover to the compressor. This capability makes TEVs suitable for variable-load systems.

Step-by-Step Solution:

Verification / Alternative check:
Field commissioning targets a superheat setpoint (e.g., 5–8 K). Stable SH and evaporator pressure indicate correct operation.

Why Other Options Are Wrong:

Only constant-load suitability is wrong; TEVs excel at handling variable loads.They do not directly control evaporator temperature; they control superheat (an indirect safeguard).They are not relief valves nor condenser subcooling controllers.

Common Pitfalls:
Improper bulb placement or poor thermal contact leads to hunting. Excessive pressure drop in distributors can also destabilize control.

Final Answer:

It meters refrigerant so the evaporator is properly fed and effectively filled across varying loads