superheat6k
Well-known member
'Thermostatic Expansion Valve' (sometimes termed TRV - Thermostatic Regulating Valve). Used on larger commercial systems to control the flow from the High to Low pressure side, and is usually set to control the Superheat of the suction returning to the compressor (at ~6K incidentally) instead of a capillary tube used on the vast majority of smaller domestic style fridges and freezers.
Because the pressure change occurs in a relatively small orifice any trace moisture can easily freeze on the outlet side of the orifice leading to a partial blockage to flow. Whereas with a capillary the pressure change is more gradual through the capillary where external ambient conditions mean freezing at one point is less likely, but it can still occur if a system is laden with moisture (commonly from traces of air left behind when proper evacuation processes are omitted).
Because the pressure change occurs in a relatively small orifice any trace moisture can easily freeze on the outlet side of the orifice leading to a partial blockage to flow. Whereas with a capillary the pressure change is more gradual through the capillary where external ambient conditions mean freezing at one point is less likely, but it can still occur if a system is laden with moisture (commonly from traces of air left behind when proper evacuation processes are omitted).