SiBE811001EB
Troubleshooting
CONVENI-PACK
324
9.1.5 Type and Principle of Electronic Expansion Valve
1. Difference between external equalizer and internal equalizer types
This difference is equal to that between saturation temperature and feeler bulb temperature
equivalent to the expansion valve outlet pressure on the internal equalizer type or to the
evaporator outlet pressure (at external equalizer connection) on the external equalizer type.
[Feeler bulb temperature] – [(Expansion valve) Outlet pressure equivalent saturation temperature]
= [Superheated degree] Internal equalizer type
[Feeler bulb temperature] – [(Evaporator) Outlet pressure equivalent saturation temperature]
= [Superheated degree] External equalizer type
Internal equalizer type: A feeler expansion valve, which incorporates a passage required to
apply the valve outlet pressure to the drive element (e.g. diaphragm).
External equalizer type: A feeler expansion valve, which serves as the connection of piping
from a control point branched in the evaporator outlet circuit to the
pressure sensing side of a control element.
2. Equilibrium of internal equalizer type
Evaporator
Feeler bulb
Evaporator outlet
External equalizer pipe
Feeler bulb
Evaporator
Evaporator outlet
External equalizer pipe
connection to be provided
150 to 200 mm to the
downstream side from the
position of the feeler bulb.
Internal-equalizer-type
expansion valve
External-equalizer-type
expansion valve
Pressure of feeler bulb (P
B
) = 0.49MPa
Diaphragm
Connecting rod
Evaporating pressure (P
1
) = 0.4MPa
Superheated degree adjusting spring (Ps) = 0.09MPa
P
B
= P
1
+ Ps
If the evaporator has no pressure drop,
the expansion valve with superheated
degree set to 5˚C will reach equilibrium
under the following conditions.
R-22 Te 0˚C P
1
= 0.4MPa
Point B: End of
evaporation, 0˚C
Point C: Superheated gas,
5˚C
Feeler bulb = 5˚C
Internal pressure
P
B
= 0.49MPa
Spring force Ps = 0.09MPa equivalent