Overview Of Compressor Unloading - Emerson VILTER MicroVission Operation And Service Manual
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Also See for VILTER MicroVission:
- Operation and service manual (116 pages) ,
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Appendix D • Compressor Sequencing Setup
Overview of Compressor Unloading
When suction pressure drops below control setpoint
(22-2=20 psig), then lowest priority compressor starts
unloading and will unload to its minimum step. When
suction pressure further drops below stop offset (22-
6=16 psig) for stop time period, then compressor will
shut off and will be placed in auto seq standby mode.
Once lowest compressor is stopped and suction pres-
sure is below unload offset, then second lowest priority
compressor will start unloading.
In this example, during unloading cycle when suction
pressure falls below a value less than suction control set-
point value (22-2 = 20 psig) for the time period of the
unload timer, then the program picks the lowest priority
compressor (Comp3) from the list and starts unloading
the compressor. The program unloads Comp3 as per
steps configured till it reaches its minimum step. Once
Comp3 is unloaded to its minimum step and suction
D − 8
Figure D-6. Compressor(s) Unload Cycle in Sequencing
MicroVission Controller • Operation and Service Manual • Emerson • 35391MV 1.3
pressure drops below stop offset for stop time period
then Comp3 shuts off and go into seq standby mode,
once Comp3 turns off then program picks second low-
est priority compressors (in this case Comp2) from all
running compressors list and starts unloading it if suc-
tion pressure is still below unload offset (22-2 = 20 psig).
Program unloads Comp2 and if suction pressure stays
below stop offset (22-6 = 16 psig) then Comp2 turns
off. Once Comp2 is turned off, Comp1 starts unloading
and will unload to its minimum load and will not turn off,
Comp1 continue running at minimum load. Refer Figure
D-6 for unload cycle.
During loading / unloading phase if the communica-
tion with any of the active / running / idle compressor is
lost then highest priority compressor logs event for the
same. Compressor with errors / trip / alarm/ load limit
conditions can be identified with its respective status
symbol.
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