9 Principles of Regulation for Displacement Compressors

Do you ever wonder how air compressor regulation actually works? The following outlines and defines nine principles of regulation used with displacement compressors.

1. Pressure Relief – the original method of regulating compressors by using a pressure relief valve to release excess air pressure into the atmosphere.
2. Bypass – similar in principle to pressure relief; rather than being released into the atmosphere, the relieved air is cooled and returned to the compressor’s inlet.
3. Throttling the inlet – limited to a small regulation range and resulting in a relatively high energy requirement, this method reduces flow by increasing the pressure ratio across the compressor.
4. Pressure relief with throttled inlet – this method combines a maximum regulation range with low energy consumption. The compressor element works with a vacuum in the inlet and low counter pressure to blow-off discharge air.
5. Start/stop – an energy efficient and effective regulation method for compressors below 5-10 kW—as long as the number of starts remains low—where the electric motor is completely stopped when the pressure reaches the upper limit and restarted when the pressure drops below the lower limit.
6. Speed regulation – an efficient method for maintaining steady outgoing pressure and low energy consumption, the compressor’s speed and flow rate are controlled by either a combustion engine, gas turbine or frequency controlled electric motor.
7. Variable discharge port – in screw compressors, this method moves the position of the discharge port toward the inlet to regulate the flow rate. However, this method results in high power consumption and is therefore rarely used.
8. Suction valve unloading – this method is used with piston compressors and regulation occurs when the inlet valves are mechanically forced open and air is pumped out into the cylinder.
9. Load—unload—stop – this method combines a large regulation range with low losses making it a common regulation principle used for compressors with a greater than 5kW capacity.

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