KEVOS® MAKEOS · Pneumatics
Compressed-Air Blow-Off Consumption (Nozzles, Air, Power and Cost)
How much compressed air do these blow-off nozzles or open pipes use, what share of the compressor is that, and what does it cost each year?
Consumption of open blow-off nozzles or pipe ends: jet velocity, choked flow and free-air flow through each opening (as the escaping air velocity tool), total flow for the nozzles at their duty, share of compressor capacity, compressor power and yearly energy cost from your specific power, and the saving from changing to engineered nozzles of a known flow.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Supply pressure (gauge) | bar | Gauge pressure behind the openings. |
| Outside pressure (absolute) | bar | Absolute pressure outside (atmosphere). |
| Air temperature | °C | Air temperature. |
| Ratio of specific heats | Ratio of specific heats (1.4 for air). | |
| Opening diameter | mm | Bore of each open pipe or nozzle orifice. |
| Discharge coefficient | Discharge coefficient (about 0.6–0.65 for drilled holes and pipe ends). | |
| Number of openings | Number of openings blowing. | |
| Share of time blowing | % | Share of running time the air flows. |
| Compressor specific power | kW per m³/min | Compressor input power per m³/min of free air. |
| Compressor capacity | m³/min | Air delivered by the compressors, as free air. |
| Running hours per year | h | Hours per year the line runs. |
| Electricity price | $/kWh | Electricity price. |
| Flow of an engineered nozzle at this pressure | L/min | Consumption (as free air) of the engineered nozzle you would fit instead (from its data sheet; 0 if none). |
Method and formulas
- Choked when p₂ ÷ p₁ < [2 ÷ (k + 1)]^(k/(k−1)); jet velocity sonic, flow ṁ = C_d A p₁ √(k ÷ R T) [2 ÷ (k + 1)]^((k+1)/(2(k−1))), as free air (as the escaping air velocity tool).
- Average flow = per opening × openings × duty; power = flow (m³/min) × specific power; cost = power × hours × price.
- Saving = (flow now − engineered flow × openings × duty) × specific power × hours × price.
- Example: each 2 mm opening blows 168.16 L/min; 6 at 50% duty use 5.0448% of the compressor and cost 3,279.1 a year.
Limitations
- Open discharge to atmosphere; long or small supply hoses lower the pressure at the opening.
- Engineered nozzle flow must be taken at the same pressure.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Cost the open pipes used for blow-off on a line
- Justify engineered air nozzles
- Check that blow-off does not overload the compressor
Who it is for
- Energy managers
- Maintenance engineers
- Production engineers
What you get
- Jet velocity and flow per opening
- Total flow, share of capacity, power and cost
- Saving with engineered nozzles
Interpreting the result
- Lowering the blow-off pressure or switching air off between parts often saves more than any nozzle change.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3037–3038, 3032–3041. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Compressed-Air Blow-Off Consumption (Nozzles, Air, Power and Cost) calculator
