How to calculate the gas consumption of equipment

The calculation of equipment gas consumption is the core link of air compressor selection and air compressor room design, and it is necessary to comprehensively consider the factors such as equipment gas consumption parameters, simultaneous utilization rate and pipeline loss. The following are detailed calculation methods and steps:

1. basic calculation: gas consumption of single equipment

1. check the equipment nameplate or instruction manual
   devices are usually labeled rated air consumption(Unit: m & sup3;/min, m & sup3;/h or CFM,1CFM & asymp;0.0283m & sup3;/min). For example:
   • pneumatic wrench: 0.5m & sup3;/min
   • spray gun: 0.3m & sup3;/min
   • automatic cylinder: single action air consumption 0.01m & sup3;, 10 actions per minute & rarr; 0.1m & sup3;/min
2. measurement method (if there is no nameplate data)
   • use flowmeter directly measure the instantaneous flow rate at the inlet of the device.
   • By pressure-time curve estimation: Record the pressure change during the operation of the equipment, and calculate the air consumption in combination with the cylinder volume or action frequency.

Calculation of Total Gas Consumption for 2. Multiple Equipment

1. simple superposition method (ideal state)
   add the rated gas consumption of all equipment to obtain the theoretical total gas consumption.
   Example:
   • device A:0.5m & sup3;/min
   • device B:0.3m & sup3;/min
   • device C:0.2m & sup3;/min
   • theoretical total gas consumption= 0.5+0.3+0.2 = 1.0m³/min
2. considering the simultaneous utilization rate (actual working condition)
   in actual production, the equipment will not run at full load at the same time and needs to be introduced. Coefficient of simultaneous use (K), the value range is usually 0.6-0.9 (adjusted according to the number of devices and frequency of use).
   Example:
   • theoretical total air consumption: 1.0m & sup3;/min
   • simultaneous use of coefficient K = 0.8
   • actual total gas consumption= 1.0 × 0.8 = 0.8m³/min

3. key correction factors

1. pipeline loss and leakage
   • insufficient pipe diameter or too many elbows will cause pressure loss, need to increase the margin of 5%-10%.
   • System leakage: The leakage rate of old pipelines may reach 10%-20%, which needs regular inspection and repair.
     Air consumption after correction= actual total gas consumption x (1 + attrition rate)
     example:
   • actual total air consumption: 0.8m & sup3;/min
   • pipeline loss rate: 10%
   • air consumption after correction= 0.8 × 1.1 = 0.88m³/min
2. gas use peak and trough
   • if the air consumption fluctuates greatly (such as intermittent painting operation), it is required maximum instantaneous air consumption selection, or buffer through the gas storage tank.
     Example:
   • instantaneous air consumption of painting line: 1.5m & sup3;/min (for 10 seconds)
   • air consumption of other equipment: 0.5m & sup3;/min
   • the air compressor with displacement ≥ 1.5m & sup3;/min shall be selected, or the air storage tank shall be equipped with balance pressure.
3. Pressure matching
   • the required pressure of the equipment (such as 0.6MPa) shall be matched with the exhaust pressure of the air compressor (such as 0.7MPa). Insufficient pressure will cause the actual air consumption to increase (because the equipment needs more air to compensate for the pressure loss).

Selection basis of 4. air compressor

1. exhaust volume (capacity)
   the rated displacement of the air compressor shall be ≥ the total air consumption after correction, and 10%-20% margin shall be reserved to cope with future expansion or leakage.
   Example:

   • air consumption after correction: 0.88m & sup3;/min
   • selection margin: 15%
   • required air compressor displacement= 0.88 × 1.15 ≈ 1.01m³/min(Optional 1.0m & sup3;/min or 1.2m & sup3;/min models)

2. exhaust pressure
   according to the highest demand pressure of the equipment, it is usually 0.1-0.2MPa higher than the required pressure of the equipment (considering the pressure drop of the pipeline).

3. Power and Energy Efficiency

   • priority is given to variable frequency air compressor, which can automatically adjust the power according to the air consumption, saving energy by more than 30%.
   • Comparing the specific power (kW/(m & sup3;/min)) of different models, the lower the value, the more energy saving.

5. practical cases

case: air compressor selection for an automobile assembly line

1. equipment List:
   • pneumatic wrench (10 sets): 0.5m & sup3;/min
   • pneumatic fixture (20 sets): 0.1m & sup3;/min
   • painting robot (2 sets): single 0.8m & sup3;/min
2. theoretical total gas consumption:
   • wrench: 10 × 0.5=5m & sup3;/min
   • fixture: 20 × 0.1=2m & sup3;/min
   • robot: 2 × 0.8=1.6m & sup3;/min
   • total: 5+2+1.6 = 8.6m³/min
3. actual total gas consumption(also using coefficient K = 0.7):
   • 8.6 × 0.7 = 6.02m³/min
4. air consumption after correction(Pipeline loss 10%):
   • 6.02 × 1.1 = 6.62m³/min
5. selection results:
   • select 2 screw air compressors (single displacement 4.0m & sup3;/min, total displacement 8.0m & sup3;/min) to meet the requirements and reserve allowance.
   • Gas storage tank (volume ≥ 2m & sup3;) shall be provided to buffer gas fluctuation.

6. considerations

1. dynamic monitoring: Install flow meter and pressure sensor, real-time monitoring of gas consumption changes, optimize the operation of air compressor.
2. Regular maintenance clean the air filter, check the tightness of the pipeline, and reduce the leakage rate.
3. Future planning: Reserve space for expansion to avoid replacing equipment again in the short term.

Through scientific calculation and reasonable selection, the efficient and stable operation of the air compressor can be ensured, while reducing energy consumption and maintenance costs.