5 most common metering devices. Metering Devices. - HVAC Online Training and Courses

Описание: In this video, I will show you the five most common types of metering devices. I will give you an explanation as to what they do and show you what they look like. This is a brief and simple explanation of their operation.
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What is a Metering Device – Specific Types of Metering Devices used in HVAC Refrigeration: Thermostatic Expansion Valve - Also referred to as the TEV or TXV for short. The thermostatic expansion valve is used in many HVAC applications including use in chillers for chilled water systems.

The piston (fixed orifice) and TXV (Thermostatic Expansion Valve) are the two most common metering devices in use today, with some modern systems utilizing an electronically controlled metering device called an EEV (Electronic Expansion Valve)

A metering device provides a pressure drop point. This device has two jobs:
It holds refrigerant back in a condensed state
It feeds refrigerant into the evaporator.

When high-pressure liquid enters a metering device, pressure starts to drop as the temperature remains the same until it reaches saturation pressure-temperature. At this time, both the pressure and temperature continue to drop to the evaporator pressure-temperature (Table 2).

Low-pressure liquid that is leaving the metering device is boiling at saturated pressure-temperature. The process of a refrigerant changing its state (from a liquid to a vapor) in the metering device is called flash gas. Flash gas is what cools the refrigerant liquid in the metering device. A system with no subcooling has more gas that is flashed and less capacity.