The Turbo Air® 3000 Centrifugal Compressor Compressor Handbook

The Turbo Air 3000 Centrifugal Compressor Handbook
Auto-Unload Control
In this Vantage control mode, inlet control is the same as Auto-Offline, but now only to the point
where the Maximum System Pressure setpoint is reached. Then, instead of blowing off, Auto-Unload
unloads the compressor. The compressor reloads as described above.
Auto-Unload Control Setpoints
Maximum Motor Load Setpoint: Prevents motor overload condition.
System Pressure Setpoint: Establishes initial pressure control point.
Surge Control Offset Line: Prevents compressor surging at minimum flow conditions.
System Pressure Offset: Sets an upper level for allowable system pressure.
Maximum Discharge Pressure: Prevents compressor surging at over-pressure conditions.
Auto-Unload Control Steps (see Figure C—3)
C—12
1. Compressor loads to achieve System Pressure setpoint (position 1).
2. When demand is low, the inlet valve throttles to the Minimum Flow line (position 2).
3. The inlet Minimum Flow control loop operates the compressor along the Min Flow control line
(B), between position 2 and the System Pressure Offset setpoint (position 3).
4. When the System Pressure Offset reaches setpoint (pos.3), the Auto-Unload control method
unloads the compressor by first fully opening the compressor discharge bypass valve, and then
closing the inlet valve to its minimum position (pos.4).
5. The compressor reloads when system pressure drops below the System Pressure setpoint.
Figure C—3: Auto-Unload Control Operation