24 – 7
Section 24
•
Twin Screw Control
Vission 20/20 • Operation and Service Manual • Emerson • 35391SC 2.7
Figure 24-7. Timers Menu - Twin Screw Control
During this time, the Prelub Oil Pressure Alarm and Trip
setpoints are forced into the Run Oil Pressure Alarm and
Trip settings. By default, the Prelub Oil Pressure Alarm
and Trip setpoints and the Run Oil Pressure Alarm and
Trip settings are the same values, however these set-
tings are adjustable. In some cases it may be advanta-
geous to set the Prelub Oil Pressure Alarm and Trip set-
points to a lower value than the Run Oil Pressure Alarm
and Trip setpoints. This will provide more time for the
screw compressor to develop running oil pressure after
the compressor starts.
After the Low Oil Pressure Safety Bypass Timer expires,
the Run Oil Pressure Alarm and Trip setpoints revert to
their normal setpoints. At this time, or anytime thereaf-
ter, if the oil pressure does not exceed the Run Oil Press
Trip setpoint, then the compressor will fail because of
“Run Oil Pressure”.
OIL PRESSURE MONITORING AFTER
COMPRESSOR STARTS
After oil pressure exists and assuming that the capacity
slide is less than 5%, the compressor now starts. During
the first 5 minutes of the compressor running, if the oil
pressure drops to the “Low Oil Pressure Trip” value (or
below) for five continuous seconds (settable by a timer
called “Oil Pressure Fail Delay” timer), then the compres-
sor will fail on “Low Run Oil Pressure” failure. After five
minutes of the compressor running, then if the oil pres-
sure ever drops to the low oil pressure trip value (or be-
low), then the compressor will immediately fail on “Low
Run Oil Pressure” failure.
Summary of Contents for Vilter Vission 20/20
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