23
3.2 Suction Line Sizing
Suction lines and suction risers must be sized to ensure
adequate velocity for oil return, taking into account the
reduction in mass flow associated with the use of a
mechanical subcooler. The lack of proper line sizing may
result in premature compressor failure due to oil slugging.
Improper suction line sizing may cause oil “logging”
which can lead to compressor failures.
3.3 Suction Pressure Range
Carlyle
®
Compound Cooling compressors are specifi-
cally designed for today’s low temperature applications.
The added advantages are its capability to also use HFC
refrigerants. The designed operating range is from -60 F
(-51.1 C) to -10 F (-24 C) saturated suction temperature.
3.4 Intermediate Pressure Range
The intermediate pressure may be calculated using the
equation in this section or the tables provided in this
guide. The intermediate pressure of the Carlyle
Com-
pound Cooling compressors will vary based on suction
and discharge pressure as well as the amount of inter-
stage flow due to subcooling and de-superheating.
When subcooling and de-superheating are employed, the
approximate intermediate pressure may be calculated by
taking the square root of the product of the suction and
discharge pressure, plus or minus ten psi.
P1 = Suction Pressure (PSIA)
P2 = Discharge Pressure (PSIA)
AIP = Approximate Interstage Pressure
If a subcooler is not used, the intermediate pressure may
be up to 30 psi (2.07 bars) lower than the AIP. In addition,
shown in tables “R-22 Approximate Interstage Pressure ±
10 psig with Subcooler” and “R-507/R-404A Approximate
Interstage Pressure ± 10 psig with Subcooler” are
approximate interstage pressures for R-22, R-404A,
R-407A, and R-507.
3.5 Discharge Pressure Range
Carlyle
Compound Cooling compressors are designed to
handle discharge pressures as high as 130 F (54 C) sat-
urated condensing temperature with R-22, R-507 and
R-404A. Low discharge pressure limit for R-22, R-507,
R-407A, and R-404A is 70 F saturated condensing
temperature.
Fig. 11 — Compound Cooling System Piping / HFC Multiple Compressor Systems
Solenoid
Valve
Expansion
Valve
Expansion
Valve
Evaporator
Subcooler
TXV
Bulb
TXV
Bulb
Condenser
Required - Set for
Pressure Equivalent of
No Lower than 70F SCT
LOW
LOW
HIGH
LOW
LOW
HIGH
Oversized High Efficiency
Coalescing Oil Separator Oil Return
to Compressor Crankcase
Discharge
Pressure Regulator
Full-Flow
Solenoid Valve
Full-Flow
Solenoid Valve
Suction
Line
AIP =
P1 x P2
