A blow-off nozzle left open all the time uses around 150 l/min, like a blow gun whose trigger is never released. Over a two-shift year, that is tens of thousands of m³ of air and several thousand kWh per nozzle. Shutting the nozzle off when the machine is idle and lowering its pressure are the two moves that pay back most.
In sawmills and the timber industry, the nozzles that clear sawdust from blades, sensors and planers are often the largest air user on site, ahead of the cylinders.
How much air does a blow-off nozzle use?
Consumption depends on the orifice diameter and the supply pressure. The exact figure is in the nozzle maker's documentation. Failing that, the usual order of magnitude for a cleaning nozzle is that of a blow gun: about 150 l/min, as a guide.
One point to remember: for the same orifice, a nozzle's flow roughly follows the absolute pressure (gauge pressure + 1 bar). That is why lowering the pressure works so well.
Working out the cost, step by step
Take a nozzle at 150 l/min, open continuously, on a line running 4,000 hours a year (two shifts, adjust to your site).
- Air per hour: 150 × 60 = 9,000 litres, or 9 m³.
- Air per year: 9 × 4,000 = 36,000 m³.
- Energy: a screw compressor such as the S 110 (11 kW, 1.7 m³/min at 8 bar) needs about 0.11 kWh per m³ according to its data sheet. 36,000 × 0.11 = about 4,000 kWh a year.
- Cost: multiply by the kWh price in your electricity contract.
That is a minimum: unloaded running, leaks and the dryer come on top. Our article on the cost of a m³ of compressed air covers those factors.
With four nozzles, the line uses 600 l/min continuously: more than a third of what an S 110 produces. That flow weighs on compressor size as much as on the bill.
Five ways to cut consumption
1. Shut the nozzle off when the machine is idle. A solenoid valve driven by the machine, or by a presence sensor, only opens the air during the cut or while the part passes. If the blade works half the time, consumption is halved.
2. Lower the pressure. A dedicated regulator on the nozzle lets you find the lowest pressure that still cleans. Going from 6 to 3 bar gauge means going from 7 to 4 bar absolute: the nozzle uses about 4 ÷ 7 = 57% of its original flow, roughly 86 l/min instead of 150. Test in steps and check the sawdust still clears.
3. Replace drilled pipes. A home-made pipe with drilled holes uses far more air than a nozzle designed for blowing. Air-amplifying nozzles, which draw in ambient air around the jet, give the same effect with less compressed air. Nozzle makers publish their consumption: compare at equal pressure.
4. Move the nozzle closer and aim it. The jet loses force quickly with distance. A nozzle close to the blade and well aimed cleans at lower pressure.
5. Blow in pulses. For a sensor or a photocell, a short regular pulse is often enough. A timer on the solenoid valve does the job.
What about the compressor?
Less blowing means fewer kWh first of all. With a variable speed compressor such as the S series, the motor slows down when demand drops, so the saving shows straight away on the bill. Our article on variable speed vs fixed speed explains why.
Sometimes it also means a smaller compressor. A line that needed 2,000 l/min before the changes, and 1,400 l/min after, moves from the S 150 (2.2 m³/min at 8 bar) to the S 110 (1.7 m³/min at 8 bar), margin included. On a multi-shift site with several lines, the S 220 PM (3.6 m³/min at 8 bar) keeps a reserve for the remaining blow-off.
Traps to avoid
- Lowering pressure across the whole network. Cylinders and clamps need it. Set pressure nozzle by nozzle, not at the compressor.
- Forgetting about water. A nozzle that spits water makes sawdust stick instead of blowing it away. A dryer after the compressor solves this.
- Measuring only once. A blocked nozzle or a solenoid valve stuck open is enough to lose the gain. Check at every service.
The leak cost calculator gives an idea of what a permanently open orifice costs, and a compressed air audit measures the real consumption of each line. To review your installation, send us your list of nozzles and machines with a quote request.
For your trade: Compressor for sawmills and the timber industry.