Flow rate Q, pressure P, and power KW are the three primary performance indicators for air compressors.

The exact airflow capacity Q and pressure P required by a user are determined by the specific air consumption of their equipment. An oversized unit constitutes waste, while an undersized one proves inadequate. Therefore, users must carefully select the model based on their equipment’s precise requirements. Even without knowing the exact model, providing approximate ranges for pressure and airflow will enable our sales representatives to make suitable recommendations. Some customers lack clarity regarding their requirements and simply request direct recommendations from sales representatives. This leaves the representative perplexed, and haphazard recommendations will prevent the user from selecting a suitable model.

Typically, the actual air consumption of the user’s equipment is calculated, then multiplied by a safety factor of approximately 1.2 to determine the air compressor’s discharge volume selection parameter. When determining pressure, one must consider not only the actual pressure required by the equipment but also pressure losses in the piping system; hence, a marginally higher pressure is advisable.

China’s Mechanical Industry Standard JB/T6430-2002 provides explicit specifications for the relationship between flow rate Q, pressure P, and motor power KW in oil-injected screw air compressors.

The discharge volume Q denotes the compressor’s air intake flow rate per minute, a conventional term referring to the air volume drawn into the compressor. For instance, an LGB-10/8 compressor strictly speaking draws 10 m³ of air per minute under standard atmospheric pressure. When converted to actual flow at 8 kg, the true discharge volume should be approximately 10 ÷ 8 ≈ 1.25 m³. Thus, the LGB-10/8’s genuine discharge volume at 8 kg is around 1.25 m³.
The approximate conversion formula between intake and discharge volumes is:

Q (High-pressure flow rate) ≈ Q (Intake flow rate/discharge volume) ÷ P (Discharge pressure)

The most scientifically accurate metric is the air compressor’s volumetric flow rate – that is, the volume of air discharged per revolution of the rotor. This serves as a definitive indicator for evaluating the quality and capacity of the compressor head.
Chinese national standards specify discharge volume per minute, creating loopholes exploited by unscrupulous manufacturers. For instance, a 10 m³ air compressor may achieve this volume at 2,960 rpm with a high-quality host unit, whereas a substandard unit requires over 5,000 rpm to deliver the same output. Consequently, even with bearings of equivalent service life, the operational lifespan is significantly reduced. Moreover, noise levels and energy efficiency are markedly inferior.

Pressure P, measured in megapascals (MPa), is typically expressed as kilograms per square centimetre by multiplying by 10. For instance, 0.8 MPa equates to 8 kg/cm².
Common air compressor power ratings include 36, 59, 88, 140, 153, 162, 191, 221, and 264 kW. These primarily correspond to diesel engine power bands. Diesel engines for air compressors are typically standard models, with few custom power ratings developed specifically for compressor manufacturers—except in cases of deep collaboration or for world-leading brands.
Two of the following parameters must be specified: Q (airflow), P (pressure), and kW (power). Without these, it is impossible to discuss specifications with clients or provide quotations. This is because air compressors with identical airflow but differing pressures carry significantly varying prices, sometimes with substantial discrepancies.