Vermeulen brings nearly 20 years of experience in the refrigeration industry specialising in load calculations, refrigeration and heat exchanger design, Danfoss ADAP- KOOL systems, as well as rack design and efficiency optimisation.

His session highlighted a central truth: while compressors and condensers often receive the most attention, it is the expansion valve that ultimately governs how effectively a system responds to load, protects itself and performs over time.

UNDERSTANDING THE EXPANSION VALVE’ S FUNCTION

Every refrigeration system is built around four fundamental components: the compressor, condenser, evaporator and expansion valve. While each plays a distinct role, the expansion valve is responsible for enabling the cooling process itself. By creating a pressure drop between the highpressure liquid line and the low-pressure evaporator, it allows the refrigerant to enter a state where it can boil at a lower temperature. This phase change absorbs latent heat, creating a cooling effect, and is fundamental to refrigeration.

At the same time, the expansion valve regulates the flow of refrigerant into the evaporator. This balancing act is critical. Too little refrigerant leads to inefficient heat transfer and excessive superheat, while too much introduces the risk of liquid refrigerant returning to the compressor, potentially causing mechanical damage. Maintaining this equilibrium ensures that the compressor

operates within its design envelope, preserving both efficiency and lifespan.

Historically, refrigeration systems relied on rudimentary expansion devices such as capillary tubes and hand-operated valves. These solutions were simple and costeffective but lacked the ability to respond to changing load conditions. Before the invention of TEVs, larger systems often required dedicated operators to manually adjust valves in response to temperature fluctuations – an approach that was both labour-intensive and imprecise.

The development of the TEV in the early 20th century marked a turning point. By introducing automatic control based on superheat, TEVs eliminated the need for constant manual intervention – with the first patent filed 24 August 1927 by Harry Thompson. The principle has since remained largely unchanged for nearly a century. A sensing bulb, mounted at the evaporator outlet, detects temperature and generates pressure that acts on a diaphragm. This pressure competes with

evaporator pressure and a calibrated spring, creating a dynamic balance that determines the valve opening.

Despite their mechanical simplicity, TEVs are remarkably effective within their operating range. However, their limitations become evident in systems with highly variable loads or demanding performance requirements.

CONTROL CHARACTERISTICS AND PRACTICAL LIMITATIONS

The behaviour of a TEV is governed by the interaction of three forces: the bulb pressure that opens the valve, and the evaporator and spring pressures that act to close it. This balance allows the valve to maintain a relatively stable superheat under steady conditions, but it also introduces constraints.

One of the most significant challenges is the phenomenon known as‘ hunting’. This occurs when the valve is unable to stabilise around a target superheat and instead oscillates between overfeeding and starving