The Turbo Air® 3000 Centrifugal Compressor Compressor Handbook

The Turbo Air 3000 Centrifugal Compressor Handbook
Auto-Offline Control
Inlet Valve Control
When the actual system pressure is lower than the System Pressure Setpoint, the Vantage controller
begins to load the compressor. During the initial load cycle, the inlet valve opens to a Minimum Flow
value when the compressor discharge valve begins closing.
During this initial load cycle, the Inlet Maximum Load control loop controls the inlet valve and quickly
loads the compressor within the Maximum Motor Load setpoint constraints.
Note: The proper Motor Load setting for 1.15 service factor motors is 112% of motor full
load amps (FLA).
As the system air pressure approaches the System Pressure setpoint, the Inlet System Pressure control
loop obtains control of the inlet valve (if the motor amps are below maximum).
In cases of low air demand, Inlet System Pressure control loop maintains the System Pressure setpoint
by reducing the compressor output through inlet valve throttling moves. This throttling continues
until the compressor reaches its minimum stable operating point, and the Inlet Minimum Flow control
loop resumes automatic control of the inlet valve.
In the Minimum Flow control loop, the inlet valve is controlled along the minimum flow Surge Control
Offset line, a user-set specific offset along the entire actual surge curve.
An important aspect of the Minimum Flow control loop, is that the actual system pressure is allowed
to increase above the System Pressure setpoint, to the System Pressure Offset setpoint. When the
measured pressure reaches the System Pressure Offset value, Auto-Offline then smoothly transfers
control to the compressor discharge valve control loops.
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