Compressor Speed–Pressure Relationship Diagram

The Basic Relationship Between Rotational Speed and Pressure

During operation, the rotational speed of an air compressor typically affects the host unit’s discharge capacity and the rate at which pressure builds up. When air demand at the point of use remains relatively stable, increasing the speed generally accelerates compressed‑air delivery, making it easier to keep system pressure within the set range; conversely, reducing the speed decreases the air output, and the pressure rise becomes correspondingly slower.

It should be noted that pressure is not determined solely by rotational speed. In practice, it is also influenced by factors such as air consumption, storage tank volume, pipeline resistance, leakage rates, control strategies, and the setpoint pressure. Consequently, trend‑based diagrams are best used to identify patterns rather than being interpreted as rigid formulas.

Common ways of expressing relationships in diagrams

• The horizontal axis represents rotational speed:Used to observe the operational changes of equipment under different rotational speeds.
• The vertical axis represents pressure:Used to determine whether the system pressure meets the gas demand.
• Curve trend:Under identical operating conditions, pressure typically builds more rapidly as rotational speed increases; however, if air consumption rises in tandem, the pressure may not increase proportionally.
• Set the interval:The diagram typically indicates the upper and lower pressure limits or the target control range, thereby illustrating the equipment’s pressure control span.

Key factors influencing curve variation

• Gas flow fluctuations:If the gas consumption at the end point fluctuates significantly, the pressure may still vary even when the rotational speed remains stable.
• System Volume:When the gas storage tank and piping have large volumes, pressure fluctuations are typically more gradual.
• Leakage situation:Leaks in piping or fittings increase air consumption and make it more difficult to maintain pressure.
• Intake conditions:Intake air temperature, filtration resistance, and ambient conditions all affect the actual output capacity.
• Control method:Operating at mains frequency, employing on/off control, or utilizing variable-frequency regulation can each result in distinct speed and pressure characteristics.

Rotational Speed and Pressure Under Variable-Frequency Control

In variable-frequency‑controlled air compressor systems, the rotational speed is adjusted in response to air demand. When air consumption increases, the equipment may boost its speed to meet the higher demand; when air consumption decreases, the speed may be reduced to minimize unnecessary energy consumption.

The key to this control strategy is not simply to achieve high rotational speed, but to ensure that the speed closely matches the actual air demand. If the speed remains consistently too high while pressure remains unstable, it may be necessary to verify whether the air demand, pipeline leaks, pressure settings, or system configuration are appropriate.

Reading the Diagram and Application Recommendations

• First, verify that the pressure is within the normal control range, then determine whether the speed changes are consistent with the variations in air consumption.
• If the pressure remains consistently low, don’t focus solely on the rotational speed; also check whether the air consumption at the point of use exceeds capacity, whether there are leaks, or whether the filter resistance is excessively high.
• If pressure fluctuations are frequent, a comprehensive analysis should be conducted, taking into account the gas storage volume, the load‑unload control logic, and the inverter’s response characteristics.
• The curves may vary depending on the aircraft type and control logic; therefore, they should be evaluated in conjunction with the equipment manual and field operating data.