Metering Devices Flashcards
Types of metering devices
- Capillary tubes
- Metering orifice
- TXV (thermostatic expansion valve)
- EEV (electronic expansion valve)
- AXV (automatic expansion valve)
- High side float/Low side float
- Hand valve
Internally equalized TXV
Used on single circuit evaporators
Only the bulb in on the evaporator outlet
Externally equalized TXV
Used in multiple circuit evaporators for reduced pressure drop
Uses sensing bulb and piped directly into outlet of evaporator
Closing force in a TXV
Evaporator pressure
Spring pressure
Opening force on a TXV
Bulb pressure
Nick named superheat valve
What is the typical superheat range ?
8-12
What metering device uses a thermistor ?
Electronic expansion valve
Simplest metering device is what ?
Fixed orifice
What orifice design does a hand valve use to meter refrigerant ?
Needle type orifice
What metering devices are used for critically charged systems ?
High side float
Automatic expansion valve
Capillary tube
Sensing bulb, LIQUID CHARGE
Contains same refrigerant as system
Contains enough liquid/vapor for wide range of temps
Sensing bulb, CROSS LIQUID CHARGE
bulb contains different refrigerant than system
Refrigerant in bulb will not follow PT relationship of system
Sensing bulb, VAPOR CHARGED
bulb contains Same refrigerant as the system
Critically charged bulb
(Pressure limiting or MOP valve)
Sensing bulb, CROSS VAPOR CHARGE
bulb contains different refrigerant than system
Refrigerant in bulb will not follow PT relationship throughout system
Types of EEVS
Stepper motor valve - modulates in tiny increments
Solenoid valve - pulses rapidly open and close. Can be used in place of LLSV
