Rarely does the compressed air demand match the supply of the compressor system. To keep the generation costs down and the system efficiency as high as possible Compressor Controls are utilized to maximize the system performance, taking into account system dynamics and storage. I will touch on several methods briefly, and leave the reader to delve deeper into any type of interest.
- Start/Stop – Most basic control – to turn the compressor motor on and off, in response to a pressure signal (for reciprocating and rotary type compressors)
- Load/Unload – Keeps the motor turning continuously, but unloads the compressor when a pressure level is achieved. When the pressure drops to a set level, the compressor reloads (for reciprocating, rotary screw, and centrifugal type)
- Modulating – Restricts the air coming into the compressor, as a way to reduce the compressor output to a specified minimum, at which point the compressor is unloaded (for lubricant-injected rotary screw and centrifugal)
- Dual/Auto Dual – Dual Control has the ability to select between Start/Stop and Load /Unload control modes. Automatic Dual Control adds the feature of an over-run timer, so that the motor is stopped after a certain period of time without a demand.
- Variable Displacement (Slide Valve, Spiral Valve or Turn Valve) – Allows for gradual reduction of the compressor displacement while keeping the inlet pressure constant (for rotary screw)
- Variable Displacement (Step Control Valves or Poppet Valves) – Similar effect as above, but instead of a gradual reduction, the change is step like (for lubricant injected rotary types)
- Variable Speed – Use of a variable frequency AC drive or by switched reluctance DC drive to vary the speed of the motor turning the compressor. The speed at which the motor turns effects the output of the system.
In summary – the primary functions of the Compressor Controls are to match supply to demand, save energy, and protect the compressor (from overheating, over-pressure situations, and excessive amperage draw.) Other functions include safety (protecting the plant and personnel), and provide diagnostic information, related to maintenance and operation warnings.
If you would like to talk about compressed air or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.