HPS Rotary Screw Compressor Units
070.700-IOM (MAR 21)
Page 22
Operation
Notice
For alarm descriptions and shutdown or cutout pa-
rameters, see publication 090.040-O.
Compressor oil separation system
The HPS is an oil-flooded screw compressor. Most of
the oil discharged by the compressor separates from the
gas flow in the oil charge reservoir. Some oil, however,
is discharged as a
mist, which does not separate readily
from the gas flow and is carried past the oil charge reser-
voir. One or more
coalescer filter elements then coalesce
the oil mist into droplets, which fall to the bottom of the
coalescer section of the oil separator. See
return of this oil to the compressor is controlled by a
throttling valve on both high stage and booster applica
-
tions.
Notice
Open the throttling valve only enough to keep co-
alescer end of separator free of oil.
Leave the
sight glass located near the bottom of the
coalescer section of the oil separator empty during normal
operation. If an oil level develops and remains in the sight
glass, a problem in the oil return separation system or
compressor operation has developed. See
for
information on how to correct the prob lem.
Notice
The normal operating level is midway between the
two sight glasses located midway along the oil separa-
tor shell.
Figure 26: Oil separation system
Cold-start system (580 psig DWP)
The HPS package is equipped with a special "cold-start"
discharge check valve (see
) on the
gas outlet
connection of the oil separator. This valve causes the oil
separator to develop oil pressure rapidly on initial start in
order to lubricate the compressor without requiring an oil
pump, even in cold ambient temperatures with all pres-
sures equalized.
For cascade and heat pump package
s
, the cold-start
valve is equipped with a large spring that creates 30 psi of
pressure in the oil separator (above suction pressure), for
lubrication of the compressor.
After the compressor is operational, it forces gas to the
condenser at connection P2. As the condenser heats
up, pressure begins to rise as the compressor suction
pulls down in pressure. As soon as differential pressure
is developed between the condenser and suction, these
pressures act across a piston inside the cold-start valve to
partially overcome the spring force. When the differential
pressure reaches and exceeds 30 psi, the piston fully over-
comes the spring force and powers the valve fully open for
very low operating pressure drop.
The HPS package is also equipped with a
suction check
valve bypass. The oil separator slowly bleeds down to
approximate system suction pressure when the unit is
stopped. This allows the compressor drive motor to have
an easier start, and the
discharge check valve seats more
tightly. See the
section for
operation.
Notice
For alarm descriptions and shutdown or cutout pa-
rameters, see publication
090.040-O
.
Figure 27: Cold-start valve
Notice
The solenoid coil can be serviced or replaced with-
out evacuating the package. However, if the hydraulic
solenoid valve or manifold block need to be serviced
or replaced, then the compressor package must be
evacuated.
Notice
To control the rate of loading and unloading, change
cycle time, proportional band, and dead band
setpoints with Quantum HD control.