Brochure

Bulletin 110-10 – Page 3
DESIGNING THE LOW PRESSURE OIL
RETURN SYSTEM
Oil must be present to lubricate the compressor. However, oil
becomes a detriment to system performance if present in large
quantities in the evaporator. Therefore, it’s necessary to control
the distribution of oil within the system.
In multi‑compressor parallel systems, oil levels must be main‑
tained in each compressor regardless of the individual compres‑
sor’s oil consumption rate. Oil pumped by compressors may
vary considerably, depending on the compressor model, age and
operating conditions.
When oil is pumped by the compressor, it flows through the
common discharge header to an oil separator. The oil separator’s
function is to separate the oil from the discharge gases. Because
the oil separator does not have a large holding capacity, the oil is
transferred to an oil reservoir.
As it passes from the oil separator to the oil reservoir, the oil is at a
high discharge pressure. This pressure must be reduced to a pres‑
sure slightly higher than the compressor crankcase. The pressure
in the oil reservoir is reduced by boiling the refrigerant in the oil,
and relieving the pressure above the oil through a vent line to the
suction header. The pressure in the oil reservoir is maintained,
slightly above the suction header pressure, by means of an Oil
Differential Check Valve installed in the vent line. At its reduced
pressure the oil is then fed to the Oil Level Control which meters
the oil to the compressor equal to its pumping rate, and thereby
maintains the oil level specified by the compressor manufacturer.
The Oil Level Control functions by adding oil when the level is
low – it cannot correct an oil level that is too high.
To obtain proper oil return, each of the oil system components
must be selected according to the requirements of the overall oil
control system.
OIL LEVEL CONTROL SYSTEM
Sporlan’s Oil Level Control System components
were developed to offer the refrigeration industry
an oil level control system of the highest quality.
The heart of the system is the Oil Level Control
which, when matched with the Oil Reservoir,
Check Valve, OF Oil Filter and perhaps the
Y1236-C Pressure Differential Valve, maintains a
minimum oil level in the compressor crankcase
during all phases of system operation.
FEATURES AND BENEFITS
Externally adjustable oil level controls
Oil Level Control – Suitable for up to 90 psi
differential pressure, optional oil level equalization
connection
High performance oil filters
Choice of settings on Pressure Differential Check
Valve
Externally adjustable Y1236-C allows for desired
differential above suction pressure
Oil Reservoirs, and OF Oil Filters – UL Listed
Oil Level Controls - UL Recognized
Numerous adaptors available for various types
of compressors
Independent
Suction
OF-303, or ROF-413-T
Oil Filter
Oil Differential Check Valve
POR Oil Reservoir
Location of
OF-303-BP
Common Discharge Header
Common Suction Header
To
Condenser
Oil Separator
Oil Level Controls
Figure 1
Low Pressure Oil Return System
A
B
D
E
C
D D