(Podcast) TXV Operation, Diagnosis, and Failure w/ Jamie Kitchen

Описание: (Audio Only) In this episode of the HVAC School podcast, Bryan talks with Jamie Kitchen from Danfoss about TXV Operation, Diagnosis, and Failure.

As fixed orifices become a dying breed with the development of higher-efficiency systems, TXVs take over the mantle as the primary method of expansion. Expansion valves meter the flow of refrigerant by aiming for a certain suction line superheat value. Unlike a fixed orifice, which has an opening of a constant diameter, an expansion valve adjusts the opening size to the evaporator based on suction superheat readings.

TXVs have a sensing bulb, diaphragm, spring, and cap tubes. Various pressures act on these components: bulb pressure, spring pressure, and evaporator pressure. The sensing bulb picks up the suction superheat adjusts its pressure on the diaphragm based on the superheat it detects. Spring pressure and evaporator pressure act against the bulb pressure. The combination of all three pressures (bulb vs. spring + evaporator) dictates the opening of the TXV orifice into the evaporator. The bulb pressure is an opening force, and the spring and evaporator pressures are closing forces.

You can cause TXV failure by adjusting it or brazing it in improperly. When too much heat is applied to the TXV, the components inside can warp. Some TXV failures also occur due to contamination. Flowing nitrogen while brazing flushes carbon and oxygen contaminants out and reduces your risk of TXV failure later on.

Bryan and Jamie also talk about:

TXV anatomy (powerhead, spring, etc.)
Internal vs. external equalization
Pressure drop across the distributor
Subcooling and its relationship with the TXV
Solenoid and ball valve (upstream) malfunctions
Filter-dryer placement
TXV assessment during commissioning
Locating restrictions
Residential system airflow

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