What is the air compressor’s air delivery rate?
Displacement, commonly referred to as free‑air delivery in the air compressor industry, is the volume of gas discharged by the compressor per unit time, converted to the intake conditions at the specified discharge pressure. It is one of the key parameters for assessing an air compressor’s capacity and efficiency, directly determining whether the equipment can meet the actual compressed‑air demands of production.
Basic methods for calculating gas production volume
The calculation of an air compressor’s air output is primarily divided into two methods: theoretical and actual. Understanding the differences between these two approaches helps to more accurately assess equipment performance.
- Theoretical gas production: Refers to the volume of gas swept by the compressor per unit time under ideal conditions. It is typically calculated based on the cylinder’s geometric dimensions and rotational speed. This calculation does not account for practical factors such as gas leakage, heating, and resistance.
- Actual gas production volume: Refers to the actual gas volume delivered by the compressor during operation. Due to factors such as clearance volume, gas leakage, suction-side resistance, and temperature rise, the actual gas output is always less than the theoretical capacity. The ratio between the two is known as the volumetric efficiency.
Key factors affecting actual gas production volume
In practical applications, the air compressor’s air output is not constant; rather, it is influenced by a variety of environmental and operational parameters.
- Suction temperature and pressureThe higher the suction temperature, the lower the gas density, and the smaller the actual mass of gas drawn in; a decrease in suction pressure also results in reduced intake volume.
- Exhaust pressureThe higher the exhaust pressure is set, the greater the relative proportion of gas leakage becomes, and the more the high-pressure gas in the clearance volume expands, occupying a larger portion of the suction space; as a result, the actual gas output decreases.
- Equipment Wear and Sealing PerformanceAs operating time increases, wear of components such as piston rings and valves leads to increased internal leakage, reducing volumetric efficiency and, consequently, decreasing gas production.
- Speed fluctuationFor compressors without variable-frequency drive control, fluctuations in grid voltage or belt slippage that cause a reduction in rotational speed will directly result in a proportional decrease in air output.
How to Calculate Actual Gas Demand
To ensure proper air compressor selection, it is necessary to accurately calculate the actual air demand of the end-use equipment and then work backward to determine the required air production capacity.
- Gas-using equipment for statistical purposesList all equipment requiring compressed air and determine the average and peak air consumption of each unit per unit time.
- Calculate the total gas consumption: Sum the gas consumption of all equipment and apply a demand factor. If the equipment does not operate at full load simultaneously, multiply the total by an appropriate demand factor.
- Reserved pipeline network lossesCompressed air experiences leakage and pressure drop during pipeline transmission, so it is generally necessary to add a certain margin to the total air consumption.
- Consider future scalabilityIf there are plans to add gas‑powered equipment in the future, sufficient capacity reserve should be factored into the design based on the calculation results to avoid redundant investments in the short term.