The Turbo Air® 3000 Centrifugal Compressor Compressor Handbook

Auto-Standby Control
Vantage Control System Logic
The Auto-Standby control method is for air systems that experience dramatic variations in demand yet
do not have a lot of receiver capacity. In these cases, an unloaded compressor may not be able to
respond fast enough to sudden increases in demand.
Auto-Standby handles this situation by partially unloading the compressor to a user-set level below the
required system pressure. To take advantage of this feature, the compressor must have a modulating
blow off valve.
Operational Characteristics
Auto-Standby control is identical to Auto-Offline control (detailed previously), until the situation
where the discharge check valve closes during blow off, under Blow Off System Pressure control. At
this point, Auto-Offline unloads the compressor.
However, in the Auto-Standby mode, the compressor is not allowed to unload. Instead, the controller
will continue to open the compressor blow off valve after the check valve has closed.
Blow off continues until the compressor discharge pressure drops to a user-set level below the System
Pressure setpoint.
The control setpoint for Auto-Standby is called the Standby Mode Offset, and it is a DP value.
For example: Where the system pressure setpoint is 115 psig, and the desired standby pressure is 105
psig, input a Standby Mode Offset of 10 psig.
The compressor continues to operate at the reduced standby pressure until the actual system pressure
drops to a level below the System Pressure setpoint. When this happens, the unit will fully load
through the inlet valve control loops.
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