Service manual

24 – 4
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0
Section 24 • Twin Screw Control
Twin Screw Oil Pressure
The twin screw compressor has two separate oil pressure
settings. They are named “Prelub Oil Pressure” and “Run
Oil Pressure” in the Alarm and Trips Menu. Both of these
oil pressures are calculated in the same way - defi ned as
“Filter Outlet Pressure minus Discharge Pressure.
As shown in Figure 24-4, the alarm and trip setpoints for
both of these oil pressures are set to the same values and
any adjustments to these oil pressures is usually done so
that the setpoints are the same.
OIL PRESSURE MONITORING BEFORE
COMPRESSOR STARTS
Pressing the Auto or Manual button will start the oil
pump. The decrease solenoid will be energized as well
if the capacity slide is greater than 5%. A prelub oil pres-
sure timer called “Minimum Compressor Prelub Time”
begins timing, see Figure 24-5. This timer is adjustable
where the default time is 5 seconds. This timer allows oil
to be pushed into the oil injection lines to fi ll the lines
with oil BEFORE the system starts looking for prelub oil
pressure. After the Minimum Comp Prelub Timer times
out, then prelub oil pressure monitoring begins. The oil
pump will run for the time setting of “Prelub Oil Pressure
Monitor Time” (typically 20 seconds) trying to achieve
prelub oil pressure. If it fails to establish prelub oil pres-
sure, the oil pump shuts down for 10 seconds, and
then starts and tries again. The cycle is repeated for the
“Prelube Oil Pressure Monitor Trials” setting, typically
set at “3” tries. After the third unsuccessful try, a failure
message “Prelub Oil Pump Inhibit” is generated. This in-
dicates a failure to establish Prelub Oil Pressure. When
the Prelub Oil Pressure is established, then the compres-
sor is commanded to start.
LOW OIL PRESSURE SAFETY BYPASS
When the compressor starts, then the Low Oil Pressure
Safety Bypass timer is started (set at 60 seconds by de-
fault, but it is adjustable).
During this time, the Prelub Oil Pressure Alarm and Trip
Figure 24-4. Prelub Oil Pressure and Run Oil Pressure Settings