Thermostatic expansion valve

Air Conditioning and Heat Pumps · Condensate System · printed page 219 (PDF page 220)

Book index entries

Thermostatic Expansion Valve Thermostatic Expansion Valve for Air Conditioning Evaporator Coil Evaporator Coil – for Air Conditioning

Text in the illustration

refrigerant refrigerant refrigerant into
sensor (or feeler) bulb clamped to suction line and covered with insulation
suction line
to compressor
evaporator coil
blower
liquid line
from condenser coil
thermostatic expansion valve
A
suction line too cold (too much liquid in evaporator to boil off properly) - decreased pressure above diaphragm causes valve to close
diaphragm
spring
valve
refrigerant
B
feeler bulb senses enough heat in suction line - diaphragm pushes valve open (allowing more refrigerant into evaporator coil)
note:
mechanism simplified for clarity

Generated explanation

The illustration shows a thermostatic expansion valve controlling refrigerant flow from the condenser liquid line into an evaporator coil, with a blower moving air across the coil. A sensor bulb clamped to the suction line and covered with insulation connects to the valve diaphragm through a small tube. Cutaway A shows decreased pressure above the diaphragm closing the valve when the suction line is too cold and too much liquid remains in the evaporator to boil off properly. Cutaway B shows bulb pressure pushing the diaphragm and opening the valve when the suction line has enough heat, admitting more refrigerant to the evaporator. Arrows indicate refrigerant flow, and the valve mechanism is explicitly simplified for clarity.

Components

thermostatic expansion valve evaporator coil blower suction line liquid line sensor bulb sensor bulb connecting tube diaphragm spring valve

Materials

refrigerant insulation