21
3.8 Pressure Differential (∆P) Required to Load
Compressor
A minimum ∆P between the discharge and suction pres-
sure is required to compress the unloader valve spring
to load up the cylinder bank. While this differential pres-
sure is low, it should be evaluated for certain low head
pressure applications such as R-12, R-134a, air condi-
tioning applications or the low stage of booster applica-
tions. The discharge pressure must be higher than the
suction pressure in Table 4 (Page 20) for the unloader
assembly to load up.
Suction cut-off unloading is an option for all four and six
cylinder Carlyle 06D/E compressors. The capacity con-
trol operation and application requirements are found in
the System Design section (Section 1.0) of this manual
and should be carefully reviewed.
3.9 Electric Solenoid Capacity Control Operation
The electrically operated control valve is actuated by
remote signal to the electric solenoid coil. Each valve
controls 2 cylinders (1 bank). No manual adjustments to
the electric unloader valve are necessary. When the sole-
noid is “de-energized”, the passageways in the valve are
aligned for “loaded” conditions. When the solenoid is
“energized”, the valve passageways are aligned for
unloading.
This capacity control valve is controlled by an electric
solenoid. When the solenoid is de-energized, the valve
loads the cylinder bank (2 cylinders) as shown in
Figure 12.
When full capacity is desired, an external controller de-
energizes the solenoid coil, allowing the discharge pres-
sure to build-up behind the unloader piston assembly.
This will compress the unloader valve spring, opening
the unloader suction port. Suction gas can now be
drawn into the cylinders, running the bank fully loaded.
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