Relationship between gas production of the same air compressor under different pressures

The relationship between the gas production of the same air compressor under different pressures can be explained by the following logic and principles, the core of which is to understand the dynamic balance between the exhaust pressure, volume flow, power consumption and efficiency of the air compressor:

1. Basic principle: the inverse relationship between pressure and gas production

the gas production of the air compressor (usually refers to the volume flow, such as m & sup3;/min or CFM) and the exhaust pressure are inverse relationship. Namely:

• pressure increases and gas production decreases;
• pressure decreases and gas production increases.

Reason:
the compression process of the air compressor follows the laws of thermodynamics. When the exhaust pressure increases, the compression ratio (exhaust pressure/intake pressure) increases, and the compressor needs to consume more energy to overcome the gas resistance, resulting in compression per unit time. The volume of gas is reduced. Conversely, when the pressure is reduced, the compression process is easier and the gas production increases.

2. Specific relationship: pressure-flow curve

the performance of the air compressor is usually pressure-flow curve the curve is provided by the manufacturer and reflects the actual gas production under different pressures. For example:

• rated pressure: The standard exhaust pressure of the air compressor design (e. g. 7bar).
• Rated flow: Gas production at rated pressure (e. g. 10m & sup3;/min).
• When the pressure rises: The flow rate may drop to 8m & sup3;/min (at 8bar) or lower.
• When the pressure decreases: The flow rate may rise to 12m & sup3;/min (at 5bar) or more.

Curve shape:
the flow decreases gradually with increasing pressure, but the rate of decrease may vary depending on the compressor type (piston, screw, centrifugal). For example:

• screw air compressor: The flow rate drops more gently, suitable for scenarios with small pressure fluctuations.
• Piston air compressor: The flow drop may be steeper, suitable for fixed pressure requirements.

3. Influencing factors: the trade-off between power and efficiency.

• Power consumption: When the pressure rises, the air compressor needs more power to maintain the compression process, but the gas production decreases, resulting in energy consumption per unit of gas production (specific power) increased. For example, when the pressure rises from 7bar to 8bar, the power may increase by 10%, but the flow rate will only decrease by 5%, and the overall efficiency will decrease.
• Motor load: The pressure increase may cause the motor to overload. The pressure needs to be adjusted by frequency conversion control or unloading valve to avoid equipment damage.
• Leakage and internal pressure: Under high pressure, the system leakage rate may increase, further reducing the actual gas production.

4. Adjustment strategies in practical applications

• pressure setting optimization: Adjust the exhaust pressure according to the gas demand to avoid excessive pressure leading to waste of energy consumption. For example, pneumatic tools usually require 6-7bar and do not need to be set to 8bar.
• frequency conversion control: Adjust the motor speed through the frequency converter, so that the air compressor can automatically adjust the gas production when the pressure changes, and maintain efficient operation.
• Gas tank buffer: In scenarios with large pressure fluctuations, the gas storage tank can balance supply and demand and reduce the impact of frequent start and stop of the air compressor or pressure fluctuations on gas production.

5. Example calculation

suppose a screw air compressor produces 10m & sup3 at 7bar;/min with a power of 75kW. If the pressure rises to 8bar:

• gas production: May drop to 9m & sup3;/min (10% drop).
• Power: May increase to 82kW (up 9.3 per cent).
• specific power:
  • 75kW / 10m & sup3;/min = 7.5kW/(m & sup3;/min) at 7bar
  • 82kW / 9m & sup3;/min & asymp; 9.1kW/(m & sup3;/min) at 8bar
    decreased efficiency: 21% increase in specific power, indicating higher energy consumption under high pressure.

Summary

the gas production of the same air compressor is inversely proportional to the exhaust pressure, and the increase in pressure leads to a decrease in gas production and an increase in energy consumption. In practical application, it is necessary to balance the gas production and energy consumption by optimizing the pressure setting, using frequency conversion control or gas storage tank buffer and other measures to achieve efficient operation.