Troubleshooting
SiBE811001EB
325
CONVENI-PACK
3. When the evaporator has a significant pressure drop:
If the internal-equalizer-type expansion valve with superheated degree set to 5°C is used,
what the superheated degree at the outlet of the evaporator will be?
4. If the external-equalizer-type expansion valve is used for an evaporator with a
significant pressure drop:
Pressure of feeler bulb (P
B
) = 0.49MPa
Diaphragm
Evaporating pressure (P
1
) = 0.4MPa
Superheated degree adjusting spring (Ps) = 0.09MPa
Feeler bulb
B
C
0.32MPa
If the pressure at Point C
drops to 0.32MPa, the
pressure equivalent
saturation temperature at
the Point C will be
approximately –5˚C.
In terms of pressure
equilibrium, however, the
temperature of feeler bulb
must be equivalent to 0.09 +
0.4 = 0.49MPa, that is, 5˚C.
To raise the pressure equivalent saturation
temperature at the Point C from –5˚C to
+5˚C, Point B (end point of evaporation) must
be set further upstream side, thus bringing
the superheated degree to 10˚C and
reducing the effectively usable area of the
evaporator.
Pressure of feeler bulb (P
B
) = 0.41MPa
Diaphragm
Evaporating pressure (P
1
) = 0.32MPa
Superheated degree adjusting spring (Ps) = 0.09MPa
External equalizer pipe
Feeler bulb
If the pressure at Point C drops to
0.32MPa, the pressure equilibrium will be
0.09 + 0.32 = 0.41. Consequently, if the
Point C reaches a temperature equivalent
to 0.41MPa, the operation will reach
equilibrium. In other words, the Point B
reaches a temperature of approx. –5˚C, the
Point C reaches that of approx. 0˚C, and
the superheated degree reaches 5˚C, thus
enabling effective use of the evaporator.
B
C
0.32MPa