What is a metering device and what are common types used in high-pressure systems?

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A metering device throttles the refrigerant as it moves from the high-pressure side into the evaporator, setting how much liquid (and how soon) can enter the evaporator to absorb heat. This throttling creates the needed pressure drop and ensures the evaporator receives the right amount of refrigerant to match the cooling load while preventing liquid refrigerant from reaching the compressor. In high-pressure systems, two common metering devices are used: an orifice, which is a fixed restriction that passes refrigerant based on the pressure difference, and a thermostatic expansion valve (TXV), which senses evaporator superheat and automatically adjusts its opening to maintain the desired balance between flow and load. Other components like filters, receivers, or condensers perform different roles and do not regulate flow into the evaporator.