The Thermostatic Expansion Valve

For any refrigeration system, it is the flow of the refrigerant that determines if it will operate efficiently. The refrigerant flow has to be regulated to ensure that the right amount required at any given time is available in the evaporator. The thermostatic expansion valve (TEV) is the most common device that regulates the refrigerant flow in the system. The amount of refrigerant released into the evaporator depends on the outlet temperature and pressure of the operator.

How the Thermostatic Expansion Valve Works

The Thermostatic expansion valve (TEV) forms an essential component of a refrigeration cycle. Other vital parts include condensers, compressors, and evaporators. As part of its throttling function, the TXV lowers the pressure of the refrigerant as it flows by, causing it to expand. Low refrigerant pressure leads to the liquid’s low temperature, which allows it to absorb cold room heat through the evaporator.

Throttling devices are designed to ensure that all the refrigerant evaporates to prevent the escape of the liquid into the suction port. If the liquid gets to the suction port, it could damage the compressor, leading to the breakdown of the whole system. With the TEV, the refrigerant flow is automatic and determined by the sensing bulb.

Essential Parts of a Thermostatic Expansion Valve

The sensing bulb is the focal point of the TEV. It is fixed on the suction pipe on the lower end of the evaporator. It has a special liquid that corresponds to the refrigerant used in the system. When the sensing bulb detects increased temperatures at the evaporator exit, the fluid in the sensing bulb expands, pushing down the diaphragm. The diaphragm is made of a solid and supple material that can flex to pressure the valve needle.

The superheat setting spring’s function is to counteract the pressure of the valve needle. Once the diaphragm is pushed down, the spring goes back to create constant tension. External forces from the bulb and spring and temperature from the refrigerant determine the evaporator pressure in the equalization area. Depending on the balance of the surrounding conditions, the valve will open or close to maintain a stable superheat.

The valve needle opens, allowing refrigerant into the evaporator. The size of the opening at the outlet varies as the hand moves up and down. The variation in the opening size is vital in controlling the amount of refrigerant let into the evaporator.

5 Common Thermostatic Expansion Valve Issues That Require Troubleshooting

1. Poor Valve Installation

A poorly installed valve will not function well. When you engage someone who is not a professional, the chances are that you will end up with inadequately brazed fittings and poorly mounted bulbs. Other signs of improperly installed valves include bends in the tubing and dents in the system.

2. Improper Sensor Bulb Mounting

Sensor bulbs are supposed to be tightly mounted to remain in fixed positions. A loose sensing bulb may lead to TEV overfeeding and potentially cause flooding in the compressor. Poor insulation or a lack of insulation means that the bulb can sense ambient temperature and send the wrong signal.

3. Valve Blockage

When the valve has a blockage, it means the evaporator may have to operate under low pressure, which will negatively impact its efficiency. A blocked valve may not readily detect and adequately respond to superheat changes. Some valves have removable inlet filters that can be removed and cleaned.

4. Low Bulb Charge

Low bulb charge can also cause underfeeding. An inadequate charge will not allow the bulb to have enough pressure that can drive the spring pressure to allow the valve to open. Low valve charge may cause inefficient operations in the evaporator, potentially leading to a breakdown of the entire system.

5. Superheat Setting Issues

Depending on ambient conditions, the superheat settings may not correspond to the needed operation parameters. Each specific TEV has a special rate of change per turn of the superheat spindle. Check if the settings correspond to the TEV and adjust accordingly. Such setting adjustments may need the expertise of HVAC specialists.

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The services at Dugan Air Heating & Cooling are available to residents of Franklin and the surrounding area. We specialize in AC installation, repairs, maintenance and furnace and heat pump repairs, replacement, and maintenance. Our team of highly skilled, experienced, and licensed technicians stops at nothing to exceed your expectations. Contact Dugan Air Heating & Cooling today.