Thermal Expansion Valve
A Thermal Expansion Valve (TXV or TEV) is a refrigeration component that meters liquid refrigerant flow into the evaporator and regulates superheat of the suction gas to a steady value. It throttles high-pressure liquid into low-pressure mist and dynamically adjusts flow rate to match system load, protecting the compressor and optimizing efficiency.
Located just before the evaporator coil, the TXV holds back high-pressure liquid from the condenser and controls flow based on a sensing bulb on the suction line. It maintains constant superheat across varying loads to protect the compressor from liquid ingress and optimize energy efficiency. In maintenance logs (CMMS), it is tracked for superheat settings, operating pressures, and current data to facilitate rapid troubleshooting on the shop floor.
- Valve stuck open causes excessive refrigerant flooding, high suction pressure, little superheat, and potential compressor burnout.
- Valve stuck closed restricts flow, leading to low cooling capacity, high superheat, and compressor overheating from insufficient lubrication return.
- Screen clogging from impurities causes erratic flow and a 15%-30% drop in refrigeration efficiency.
How is TXV size selected relative to nominal capacity?
Selected to allow ~20% higher refrigeration capacity than nominal to ensure stable operation across the full range without instability.
What is the minimum requirement for stable TXV regulation?
Must operate with minimal working superheating; insufficient superheat causes unstable regulation.
What are the impacts of incorrect TXV opening on COP and MTBF?
Improper opening can increase compressor power by 15%-30% (lowering COP) and shorten compressor MTBF by up to 40%.