Electronic Expansion Valves
Trevor Matthews with Emerson Canada comes on the podcast once again to talk about electronic expansion valves (also known as EEVs). He explains how they work, what they do, and how to diagnose them.
Trevor compares electronic expansion valves to TXVs on steroids; they accomplish similar tasks, but EEVs have faster response times, better accuracy, and can improve system efficiency. The valve operates on a controller, which is the “brain” of the EEV that tells it to open or close. EEVs can come in the on-off variety (pulse-width modulation) and stepper valves, which rely on a motor to control the mass flow through the metering device. Pulse-width modulators are less accurate than stepper valves because they only have two operation settings.
When installing EEVs or systems with EEVs, in many cases, the valve will point down. When brazing in stainless steel valves, you'll usually use a 30% (or higher) silver solder. It's also a good idea to wrap the valve and flow nitrogen while brazing. The bulbs of these valves MUST be insulated and strapped properly. The bulb and transducer need to be outside the refrigerated box in low-temperature conditions.
When troubleshooting EEVs, the best thing to do is start off by reading the manual; you want to understand the valve and controller. Then, check the parameters and determine where the pressure transducer and temperature probe are located.
Trevor and Bryan also discuss:
- Balance of forces and superheat control
- Solenoid valves
- How stepper motors control the mass flow
- Various refrigerants and EEVs
- Setting parameters on EEV controls
- Flux and flux-coated rods
- Evaporator feeding
- EXD-SH and EXD-U02 controllers
- Connections, cabling, and wire splices
- Expansion valve hunting
- Objectional current and electrical issues with controllers
- Battery backup vs. solenoids
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