One of the most important aspect of an efficient compressed air delivery system is effective utilization of compressor controls. The proper use of compressor controls is critical to any efficient compressor system operation. In order to reduce operating costs, compressor controls strategies need to be developed starting with minimizing the discharge pressure. This should be set as low as possible to keep energy costs to a minimum.
The compressor system is designed with maximum air demand in mind. During periods of lower demand compressor controls are used to coordinate a reduction in output that matches the demand. There are six primary types of individual compressor controls:
- Start/Stop – This is the most basic control. The start/stop function will turn off the motor in response to a pressure signal.
- Load/Unload – The motor will run continuously, but the compressor unloads when a set pressure is reached. The compressor will then reload at a specified minimum pressure setting.
- Modulating – Restricts the air coming into the compressor to reduce compressor output to a specified minimum. This is also known as throttling or capacity control.
- Dual/Auto Dual – On small reciprocating compressors, this control allows the selection of either Start/Stop or Load/Unload.
- Variable Displacement – Gradually reduces the compressor displacement without reducing inlet pressure.
- Variable Speed – Controls the compressor capacity by adjusting the speed of the electric motor.
All of these controls then control the compressor motors and they have several different starting methods.
There are several types of modern motor starters:
Full Voltage Starters: The original, and simplest method. These are similar in theory to the old knife switches, but the operator’s hands aren’t right on the connecting switch. Full line voltage comes in, and amperage can peak at up to 8 times full load (normal operating) amperage during startup. This can result in voltage dips…not only in the facility itself, but in the neighborhood. Remember how the lights always dim in those movies when they throw the switch on the electric chair? It’s kind of like that.
Reduced Voltage Starters: These are electro-mechanical starters. Full line voltage is reduced, commonly to 50% initially, and steps up, usually in three increments, back to full. This keeps the current from jumping so drastically during startup, and reduces the stress on mechanical components…like the motor shaft, bearings, and coupling to the compressor.
Solid State (or “Soft”) Starters: Like the Reduced Voltage types, these reduce the full line voltage coming in as well, but instead of increasing incrementally, they gradually and evenly increase the power to bring the motor to full speed over a set period of time. They also are beneficial because of the reduced stress on mechanical components.
The Application Engineering team at EXAIR Corporation prides ourselves on our expertise of not only point-of-use compressed air application & products, but a good deal of overall system knowledge as well. If you have questions about your compressed air system, give us a call.
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Compressor Photo Credits to Bryan Lee, Creative Commons License