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Expansion Devices and Valves

Refrigeration systems consist of four major components; these are the compressor, condenser, expansion device (usually a TX valve) and evaporator. The most commonly used expansion device is a thermostatic expansion valve (TX valve) which expands the liquid refrigerant to lower its pressure and temperature before the refrigerant enters the evaporator.

Actrol stock a variety of expansion devices available to suit many different domestic, commercial and light industrial refrigeration and air conditioning applications. Typical applications include under-bar cabinets, display fridges, walk-in coolrooms, walk-in freezers, food processing applications and beverage cooling in restaurants, shops, supermarkets, take-away stores, food manufacturers, farms, pubs and clubs.

An expansion valve is used to control the superheat of the refrigerant exiting the evaporator and is designed to maintain a set superheat in normal operating conditions.

Expansion valves do not control humidity.

Actrol expansion valves can be put into three categories:

 

Capillary Tube

Small mass produced systems are often designed with capillary tube as it is a very low cost option. Capillary tubes are not very efficient as they are not adjustable and are therefore designed for one ambient and load condition, which results in inefficient operation the majority of the time. Capillary tubes are most often found in domestic refrigerators.

 

Thermostatic Expansion Valve

This is by far the most common type of expansion device used in commercial refrigeration. The TX valve is a mechanical valve designed for a specific refrigerant that uses both temperature and pressure inputs to control the superheat. TX valves rely on a minimum pressure drop across the valve to drive the valve open. In colder weather the condenser fans may have to be cycled or speed controlled to ensure this minimum pressure drop is maintained. There are many different valve brands and series. Some valves have a fixed orifice for one capacity range only and others have removable orifices to enable one body to cater for a range of refrigeration capacities. TX valves are available with flare and solder connections as straight through or right angle connections.

 

Electronic Expansion Valve

Over the last decade electronic expansion valves and controllers have taken a substantial part of the expansion valve market due to the increased energy efficiencies they provide. The EX valve does not rely on a minimum pressure drop across the valve, as a motor drives the valve open and closed. This enables the condensing temperature/pressure to be floated down with the ambient temperature which saves energy. As much as 25% energy savings can be achieved by using an EX valve and floating the condensing temperature/pressure. EX valves require an electronic driver to operate them and are usually available as a kit to make selection simple. Usually a driver kit and an EX valve is all that is required.